SERV1706-01 July 2005
SERVICE TRAINING TECHNICAL PRESENT PRESENTA ATION
785C (1HW), 789C (2BW) OFF-HIGHWAY TRUCKS
Service Servi ce Trainin Training g Meeti Meeting ng Guide (STMG 706)
785C (1HW),7 (1HW),789C 89C (2BW) OFF-HIGH OFF-HIGHW WAY TRUCKS MEETING GUIDE 706
TEXT REFERENCE AUDIENCE
Level II--Service personnel who understand the principles of machine systems operation, diagnostic equipment, and procedures for testing and adjusting.
CONTENT This presentation provides basic maintenance information and describes the systems operation of the engine, power train, steering, hoist, and the air system and brake s for the 785C/789C Offhighway Trucks. The Automatic Retarder Control (ARC) (ARC) and the Traction Traction Control System (TCS) are also discussed.
OBJECTIVES After learning the information in this meeting guide, the serviceman will be able to: 1. locate and identify the major components in in the engine, power train, steering, hoist and the air system and brakes; 2. explain the operation of the major components in the systems; and 3. trace the flow of oil or air through the systems. systems.
REFERENCES 784C Tractor/785C Truck Service Manual 784C Tractor/785C Truck Operation and Maintenance Manual 785C Truck with High Altitude Arrangement (HAA) Operation and Maintenance Manual 789C Truck Service Manual 789C Truck Operation and Maintenance Manual Cold Weather Recommendations for Caterpillar Machines Caterpillar Machine Fluids Recommendations
SENR1485 SEBU7173 SEBU7176 SENR1515 SEBU7174 SEBU5898 SEBU6250
PREREQUISITES Interactive Video Course "Fundamentals of Mobile Hydraulics" Interactive Video Course "Fundamentals of Electrical Systems" STMG 546 "Graphic Fluid Power Symbols"
© 2005 Caterpillar Inc.
TEMV9001 TEMV9002 SESV1546
Estimated Time: 24 Hours Visuals: 216 Visuals Serviceman Handouts: 16 Data Sheets Form: SER SERV1706-01 V1706-01 Date: 7/05
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SUPPLEMENTAL MATERIAL Reference Manuals
Fluid Power Graphic Symbols User's Guide Flexxaire™ Fan Installation and Maintenance Manual Automatic Lubrication System Off-Highway Truck/Tractors Truck/Tractors Vital Information Management System (VIMS) --System Operation" Off-Highway Truck/Tractors Truck/Tractors Vital Information Management System (VIMS) --Testing --T esting and Adjusting Troubleshooting" Variable Speed Fan Clutch" Oil Renewal System" Off-Highway Truck/T Truck/Tractors ractors Brake Electronic Control System"
SENR3981 SEBC1152 SENR4724 RENR2630 RENR2631 SENR8603 RENR2223 SENR1503
Specification Sheets
785C Off-highway Truck 789C Off-highway Truck 793C Update Off-highway Truck
AEHQ5320 AEHQ5321 AEHQ5186
Salesgrams and Product Bulletins
Salesgram "Vital Information Management System (VIMS)" Training Bulletin "Caterpillar Transmission/Drive Train Oil" Product Bulletin "Reporting Particle Count By ISO Code" Salesgram "Caterpillar Extended Life Coolant" Salesgram "785C/789C/793C Mining Truck Introduction" Salesgram "Cat 769, 771, 773, 775, 777, 785 and 789 Flexxaire™ Fan Custom Attachment" Product Bulletin "793C Off-highway Truck"
TELQ4478 TEJB1002 PEJT5025 TEKQ0072 TELQ4459 TELQ4010 TEJB3060
Video Tapes
793C Off-highway Truck--Service Introduction 793C Off-highway Truck--Marketing Introduction Suspension Cylinder Charging Introduction to the Automatic Electronic Traction Aid (AET (AETA) A) 3500 Engines--EUI Service Introduction Mining Trucks--Cleanliness and Component Life
SEVN4016 AEVN3742 TEVN2155 SEVN9187 SEVN2241 SEVN4142
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Booklets
Know Your Cooling System Diesel Fuels and Your Engine Oil and Your Engine C-Series Mining Trucks--3500B Diesel Engines
SEBD0518 SEBD0717 SEBD0640 LEDH8400
Special Instructions
Repair of 4T8719 Bladder Accumulator Group" Using 1U5000 Auxiliary Power Unit (APU)" Using the 1U5525 Attachment Group" Suspension Cylinder Servicing
SEHS8757 SEHS8715 SEHS8880 SEHS9411
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TABLE OF CONTENTS INTRODUCTION .................................................. ........................................................ ......................................................................7 ..............7 WALK AROUND INSPECTION...............................................................................................11 OPERATOR'S OPERA TOR'S ST STA ATION......................................... ....................................................... ...................................................................42 ............42 ENGINE......................................................................................................................................65 Engine Electronic Control System .......................................................................................66 Cooling System.....................................................................................................................88 Lubrication System ................................................... ........................................................ ............................................................97 ....97 Fuel System.........................................................................................................................101 Air Induction and Exhaust System ....................................................... .....................................................................................106 ..............................106 POWER TRAIN........................................................................................................................111 Torque Converter .................................................... ............................................................................................................ ............................................................112 ....112 Torque Converter Hydraulic System...................................................................................115 Transmission and Transfer Gears........................................................................................124 Transmission Transmissi on Hydraulic System .................................................. .......................................128 Differential..........................................................................................................................138 Final Drives.........................................................................................................................143 Transmission/Chassis Transmissi on/Chassis Electronic Control System System .................................................. ............144 STEERING SYSTEM ..................................................... ............................................................................................................. .........................................................154 .154 HOIST SYSTEM......................................................................................................................187 AIR SYSTEM AND BRAKES .................................................. ..............................................207 Air Charging System...........................................................................................................209 Brake Systems.....................................................................................................................216 BRAKE ELECTRONIC CONTROL SYSTEM ................................................... ...................236 Automatic Retarder Control (ARC)....................................................................................239 Hydraulic Automatic Retarder Control (HARC)................................................................245 Traction Control System (TCS) ................................................... .......................................255 OPTIONAL EQUIPMENT ....................................................... ......................................................................................................263 ...............................................263 FlexxaireTM Fan ....................................................... .............................................................................................................. .........................................................263 ..263 CONCLUSION.........................................................................................................................266 VISUAL LIST ............................................... ........................................................ ...........................................................................267 ...................267 SERVICEMAN'S HANDOUTS...............................................................................................270
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785C (1HW), 789C (2BW) OFF HIGHWAY TRUCKS
© 2005 Caterpillar Inc.
1
INTRODUCTION
Shown is the 789C Off-highway Truck. The "C" Series trucks are the same as the "B" Series except for the following changes: 3500B engines, improved cab, two different Electronic Control Modules (Transmission/Chassis and Brake) and an electronically controlled hoist. The 789C also has a 40% larger cooling system with a shunt tank located above the radiator. The second generation Electronic Programmable Transmission Control (EPTC II) has been replaced with the Transmission/Chassis Electronic Control System. The Transmission/Chassis Electronic Control Module (ECM) controls the same functions as the EPTC II plus the hoist and some other functions. The Automatic Retarder Control (ARC) and the Traction Control System (TCS) control modules have been replaced with one Brake System ECM. The Brake System ECM controls both the ARC and the TCS functions. The TCS is now connected to the CAT Data Link and the Electronic Technician (ET) service tool can be used to diagnose the TCS. The load carrying capacities and the Gross Machine Weights (GMW) of the "C" Series trucks are: 785C: 118 to 136 Metric tons (130 to 150 tons) 249480 kg (550000 lb.) GMW 789C: 154 to 177 Metric tons (170 to 195 tons) 317520 kg (700000 lb.) GMW
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Shown is the right side of a 789C truck. The large air tank on the right platform supplies air for starting the truck and for the service and retarder brake system. The hoist, brake, and torque converter hydraulic tank (rear) and the transmission hydraulic tank (front) are also visible. The transmission hydraulic system is separate from all the other hydraulic systems.
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Shown is the front of a 789C truck. The 789C is similar in appearance to the 793C and may be difficult to identify from a distance. The 793C can be identified by the four air filters and the diagonal access ladder. The 789C has only two air filters and is equipped with two vertical ladders. The "C" Series trucks use a folded core radiator. The folded core radiator provides the convenience of repairing or replacing smaller individual cores.
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The truck bodies on "C" Series trucks are mandatory options. Two body styles are available for the "C" Series trucks: - A 12 degree flat floor design that provides uniform load dumping, excellent load retention, and a low center of gravity. - A dual-slope design with a "V" bottom main floor to reduce shock loading, center the load, and reduce spills. All internal wear surfaces of the truck bodies are made with 400 Brinell hardness steel. All attachment body liners are also made with 400 Brinell hardness steel. The external components of the bodies are made of steel with a yield strength of 6205 bar (90000 psi). The forward two-thirds of the body floor is made with 20 mm (.79 in.) thick 400 Brinell steel plate. The rear one-third of the body floor is made with a 10 mm (.39 in.) thick 400 Brinell sub plate and a 20 mm (.79 in.) thick 400 Brinell body grid liner plate. As an option, the grid liner plate can be made with 500 Brinell steel. The rear suspension cylinders absorb bending and twisting stresses rather than transmitting them to the main frame.
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785C/789C MAINTENANCE
v ic e 7 8 9C S er e Proc edur
WALK AROUND INSPECTION
5
WALK AROUND INSPECTION
Before working on or operating the truck, read the Operation and Maintenance Manual thoroughly for information on safety, maintenance, and operating techniques. Safety Precautions and Warnings are provided in the manual and on the truck. Be sure to identify and understand all symbols before starting the truck. The first step to perform when approaching the truck is to make a thorough walk around inspection. Look around and under the truck for loose or missing bolts, trash build-up and for coolant, fuel, or oil leaks. Look for indications of cracks. Pay close attention to high stress areas as shown in the Operation and Maintenance Manual. INSTRUCTOR NOTE: The form numbers for the Operation and Maintenance Manuals are provided under "References" on Page 2.
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10 HOURS/DAILY MAINTENANCE CHECKS Batteries
Transmission Oil Level
Steering Oil Level
Hoist, Converter and Brake Oil Level
Auto Lube Reservoir Suspension Cylinder Height
Air Filter, Restriction Indicators and Precleaners
Rear Axle Oil Level
Coolant Level Rear Axle and Brake Cylinder Breathers
Belts and Ether Cylinders Engine Oil Level
Frame For Cracks and Body Support Pads
Windshield Washer Level and A/C Filter Air Reservoir Moisture
Leaks and Trash Build-up
Wash Windows, Cab Fresh Air Filters, Seat Belt, Indicators, Gauges, Brake Tests Secondary Steering and Back-up Alarm Tire Inflation Pressure
Suspension Cylinder Height, Grease Breathers and Wheel Breathers
Fuel Level and Drain Moisture
Wheel Nuts
6
The following list identifies the items that must be serviced every 10 Hours or Daily. - Walk around inspection: Check for loose or missing bolts, leaks, and cracks in frame structures - Suspension cylinders: Measure/recharge - Transmission oil: Check level - Hoist, converter and brake system oil: Check level - Rear axle oil: Check level - Fuel tank: Drain moisture - Engine crankcase oil: Check level - Radiator: Check level and radiator core plugging - Air filters and precleaners: Check restriction indicators and precleaner dirt level - Steering system oil: Check level - Air tanks: Drain moisture - Brakes: Check operation - Indicators and gauges: Test operation - Seat belt: Inspect - Back-up alarm: Test operation - Secondary steering: Test operation
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The front wheel bearing oil level is checked and filled by removing the plug (1) in the center of the wheel bearing cover. The oil should be level with the bottom of the plug hole. The fill plug is a magnetic plug. Inspect the fill plug weekly for metal particles. If any metal particles are found, remove the wheel cover and inspect the bearings for wear. The oil is drained by removing the drain plug (2). The service interval for changing the front wheel bearing oil is 500 hours. Use only Final Drive and Axle Oil (FDAO) or Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or newer. FDAO and TDTO TO-4 provides increased lubrication capability for bearings. Check the tire inflation pressure. Operating the truck with the wrong tire inflation pressure can cause heat build-up in the tire and accelerate tire wear. Care must be taken to ensure that fluids are contained while performing any inspection, maintenance, testing, adjusting and repair of the machine. Be prepared to collect the fluid in suitable containers before opening any compartment or disassembling any component containing fluids. Refer to the "Tools and Shop Products Guide" (Form NENG2500) for tools and supplies suitable to collect and contain fluids in Caterpillar machines. Dispose of fluids according to local regulations and mandates. NOTE:
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Check the front suspension cylinders for leaks or structural damage. Check the charge condition of the front suspension cylinders when the truck is empty and on level ground. Measure the charge height of the suspension cylinders and compare the dimension with the dimension that was recorded the last time the cylinders were charged. Recharge the cylinders with oil and nitrogen if necessary. Inspect the condition of the front wheel bearing axle housing breather (1). The breather prevents pressure from building up in the axle housing. Pressure in the axle housing may cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies. Two grease outlet fittings (2) are located on the front of each suspension cylinder. The grease supply line for the Auto Lubrication System is located at the rear of the suspension cylinder. No grease outlet fittings should be located on the same side of the suspension cylinder as the grease fill location. An outlet fitting positioned on the same side of the suspension cylinder as the grease fill location will prevent proper lubrication of the cylinder. Make sure that grease is flowing from the outlet fittings to verify that the suspension cylinders are being lubricated and that the pressure in the cylinders is not exc essive. INSTRUCTOR NOTE: For more detailed information on servicing the suspension system, refer to the Special Instruction "Suspension Cylinder Servicing" (Form SEHS9411).
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On the 785C truck, an air filter housing and a precleaner are located behind the front wheels on both sides of the truck. Check the dust valves (1) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. The dust valve is OPEN when the engine is OFF and closes when the engine is running. The dust valve must be flexible and close when the engine is running or the precleaner will not function properly and the service life of the air filters will be reduced. Replace the rubber dust valve if it becomes hard and brittle. The "C" Series trucks may have the optional primary fuel filters with a water separator (2). Two primary filter/water separators are installed, one on each side of the truck. Open the drain valve at the bottom of each housing to drain the water when required. The drain interval is determined by the humidity of the local climate. Replace the filter element in each housing every 500 hours or when restricted. The filter elements are removed from the top of the housings.
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Shown is the right side of the 3512B engine used in the 784C tractor and 785C truck. Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (arrow) located in the tube between the engine oil cooler and the engine oil filters.
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Located behind the right front tire is the transmission charging filter (1), the transmission lube filter (2), and the torque converter charging filter (3). Transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4). An oil filter bypass switch is located on each filter. The transmission oil filter bypass switches provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends the signals to the VIMS, which informs the operator if the filters are restricted. The torque converter charging filter bypass switch provides an input signal directly to the VIMS. One of the three injector banks (5) for the automatic lubrication system is also in this location. These injectors are adjustable and regulate the quantity of grease that is injected during each cycle. A solenoid air valve provides a controlled air supply for the automatic lubrication system. The solenoid air valve is controlled by the Vital Information Management System (VIMS), which energizes the solenoid ten minutes after the machine is started. The VIMS energizes the solenoid for 75 seconds before it is de-energized. Every 60 minutes thereafter, the VIMS energizes the solenoid for 75 seconds until the machine is stopped (shut down). These settings are adjustable through the VIMS keypad in the cab (LUBSET and LUBMAN). INSTRUCTOR NOTE: For more detailed information on servicing the automatic lubrication system, refer to the Service Manual module "Automatic Lubrication System" (Form SENR4724).
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Shown are the transmission hydraulic tank (1) and the hoist, converter and brake hydraulic tank (2). Both tanks are equipped with oil level sight gauges. The oil level of both hydraulic tanks should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running. The lower sight gauge (3) on the hoist, converter and brake hydraulic tank can be used to fill the tank when the hoist cylinders are in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge. Inspect the hoist, converter and brake hydraulic tank breather (4), and the transmission hydraulic tank breather (behind the mud flap) for plugging. When filling the hydraulic tanks after an oil change, fill the tanks with oil to the FULL COLD mark on the sight gauge. Turn on the engine manual shutdown switch (see Visual No. 25) so the engine will not start. Crank the engine for approximately 15 seconds. The oil level will decrease as oil fills the hydraulic systems. Add more oil to the tanks to raise the oil level to the FULL COLD mark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oil level stabilizes at the FULL COLD mark. Turn off the engine manual shutdown switch and start the engine. Warm the hydraulic oil. Add more oil to the tank as required to raise the oil level to the FULL WARM mark.
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In both tanks, use only Transmission Drive Train Oil (TDTO) with a specification of TO-4 or newer. TDTO TO-4 oil: - Provides maximum frictional capability required for clutch discs used in the transmission, torque converter and brakes. - Increases rimpull because of reduced slippage. - Increases brake holding capability by reducing brake slippage. - Controls brake chatter. - Provides maximum frictional capability required for gears.
NOTICE Failure to correctly fill the hydraulic tanks after an oil change may cause component damage.
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The rear axles are equipped with double reduction planetary-type final drives (see Visual No. 122). Rotate the final drive until the cover and plug are positioned as shown. The final drive oil level is checked and filled by removing the magnetic plug (arrow). The oil should be level with the bottom of the plug hole. Fill the rear axle housing with oil before filling the final drives with oil. Allow enough time for the oil to settle in all of the compartments. This can be as much as 20 minutes during cold temperatures. The magnetic inspection plugs should be removed weekly from the final drives and checked for metal particles. For some conditions, checking the magnetic plugs is the only way to identify a problem which may exist. Use only Final Drive and Axle Oil (FDAO) or Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or newer. FDAO and TDTO TO-4 oil provides: - Maximum lubrication capability required for gears. - Increased lubrication capability for bearings.
NOTICE The rear axle is a common sump for the differential and both final drives. If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed. Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.
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The differential oil level is checked by viewing the oil level sight glass (1). The oil should be level with the bottom of the inspection hole. Two oil level sensors (2) provide input signals to the Brake ECM. The Brake ECM sends the signals to the VIMS, which informs the operator of the rear axle oil level. A rear axle oil filter (3) removes contaminants from the rear axle housing. Check the rear suspension cylinders for leaks or structural damage. Check the charge condition of the rear suspension cylinders when the truck is empty and on level ground. Measure the charge height of the suspension cylinders and compare the dimension with the dimension that was recorded the last time the cylinders were charged. Recharge the cylinders with oil and nitrogen if necessary. The second of three injector banks (4) for the automatic lubrication system is mounted o n the top rear of the differential housing. Above the lubrication injectors is a breather (5) for the rear axle. Inspect the condition of the breather at regular intervals. The breather prevents pressure from building up in the axle housing. Excessive pressure in the axle housing can cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies. INSTRUCTOR NOTE: For more detailed information on servicing the suspension system, refer to the Special Instruction "Suspension Cylinder Servicing" (Form SEHS9411).
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The cable that holds the body up is stored below the rear of the body. Whenever work is to be performed while the body is raised, the safety cable must be connected between the body and the rear hitch to hold the body in the raised position.
WARNING The space between the body and the frame becomes a zero clearance area when the body is lowered. Failure to install the cable can result in injury or death to personnel working in this area.
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The fuel tank is located on the left side of the truck. The fuel level sight gauge (arrow) is used to check the fuel level during the walk around inspection. The percentage of sulfur in the fuel will affect the engine oil recommendations. The following is a summary of fuel sulfur and oil recommendations: 1. Use API CH-4 performance oils. 2. With fuel sulfur below 0.5%, any API CH-4 oils will have a sufficient Total Base Number (TBN) for acid neutralization. 3. For fuel sulfur values above 0.5%, the new oil TBN should be a minimum of 10 times the fuel sulfur. 4. When 10 times the fuel sulfur exceeds the oil TBN, reduce the oil change interval to approximately one-half the normal change interval.
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The primary fuel filter (1) is mounted on the inner side of the fuel tank. Open the drain valve (2) to remove condensation from the fuel tank. A fuel level sensor (3) is also located on the fuel tank. The fuel level sensor emits an ultrasonic signal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonic signal to return is converted to a Pulse Width Modulated (PWM) signal. The PWM signal changes as the fuel level changes. The fuel level sensor provides the input signals to the VIMS, which informs the operator of the fuel level. A category level 1 warning (FUEL LVL LO) is shown on the VIMS display if the fuel level is less than 15%. A category level 2 warning (FUEL LVL LO ADD FUEL NOW) is shown on the VIMS display if the fuel level is less than 10%. The fuel level sensor receives 24 Volts from the VIMS. To check the supply voltage of the sensor, connect a multimeter between Pins 1 and 2 of the sensor connector. Set the meter to read "DC Volts." The fuel level sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the fuel level. To check the output signal of the fuel level sensor, connect a multimeter between Pins 2 and 4 of the fuel level sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depth and 84% at 2000 mm (78.8 in.) of fuel depth.
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Located in front of the fuel tank is the parking brake release filter (1) and the torque converter outlet screen (2). An oil filter bypass switch is located on each housing. The parking brake filter bypass switch provides an input signal to the Brake ECM and the torque converter outlet screen bypass switch provides an input signal to the VIMS. The Brake ECM sends the signal to the VIMS, which informs the operator if the filter or screen are restricted. The 789C trucks have two air dryers (3) to accommodate the larger four-cylinder air compressor. Shown is the rear of the two air dryers. The third injector bank for the automatic lubrication system is also located in this area.
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Inspect the condition of the three breathers (1) (two visible) for the brake cylinders. The third breather is located on the front brake master cylinder behind the cross tube. Oil should not leak from the breathers. Oil leaking from the breathers is an indication that the oil piston seals in the brake cylinder need replacement. Air flow from the breathers during a brake application indicates that the brake cylinder air piston seals need replacement. If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke and cause an indicator rod to extend and open the brake overstroke switch (2). The switch provides an input signal to the VIMS, which informs the operator of the condition of the service and retarder brake oil circuit. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning.
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On the 789C truck, the second air dryer (1) is located in front of the left front suspension cylinder. On the 785C truck, the only air dryer is located here. The air system can be charged from a remote air supply through a ground level connector (2) inside the left frame. Engine oil can be added at the quick fill connector (3). Use only Diesel Engine Oil (DEO) with a specification of CF-4 or newer. DEO oil with a CH-4 specification is available and should be used if possible. CH-4 engine oil: - Requires more performance tests than previous oils, such as CE or CF, and has a narrower performance band. - Can withstand higher temperatures before coking and has better dispersing capability for controlling soot. - Has better fuel sulfur neutralization capability.
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The engine oil filters (789C shown) are located on the left side of the engine. Engine oil should be added at the fill tube (1) and checked with the dipstick (2). The 785C has three engine oil filters and is checked and filled through the engine cover (see Visual No. 22). On the 789C truck, engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3). (For the 785C truck, see Visual No. 10.). The engine lubrication system is equipped with two oil pressure sensors (4). A sensor is located on each end of the oil filter base. One sensor measures engine oil pressure before the filters. The other sensor measures oil pressure after the filters. The sensors provide input signals to the Engine Electronic Control Module (ECM). The ECM provides input signals to the VIMS, which informs the operator of the engine oil pressure. Together, these sensors inform the operator if the engine oil filters are restricted. Use only Diesel Engine Oil (DEO) with a specification of (CF-4) or newer. DEO oil with a (CH-4) specification is available and should be used if possible. - CH-4 engine oil requires more performance tests than previous oils, such as CE or CF, and has a narrower performance band. - CH-4 engine oil can withstand higher temperatures before coking and has better dispersing capability for controlling soot. - CH-4 engine oil has better fuel sulfur neutralization capability.
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Shown is the 3512B engine used in the 785C truck. Three oil filters are located on the left side of the engine. The 3512B engine also has a fitting (1) that can be used to drain the engine oil that is trapped above the filters. Do not add oil through the fitting because unfiltered oil will enter the engine. Any contamination could cause damage to the engine. Aftercooler coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap that is installed at the location o f the pipe plug (2).
NOTICE When changing the engine oil filters, drain the engine oil that is trapped above the oil filters through the fitting (1) to prevent spilling the oil. Oil added to the engine through the fitting will go directly to the main oil galleries without going through the engine oil filters. Adding oil to the engine through the fitting may introduce contaminants into the system and cause damage to the engine.
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Engine oil can be added through a high speed oil change connector and will enter the oil pan through the fitting (1). An engine oil level switch (2) provides input signals to the Engine ECM. The Engine ECM provides an input signal to the VIMS, which informs the operator of the engine oil level. The oil level switch tells the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.
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The secondary fuel filters and the fuel priming pump (1) are located above the engine oil filters on the left side of the engine. The fuel priming pump is used to fill the filters after they are changed. A fuel filter bypass switch (2) is located on the filter base. The bypass switch provides an input signal to the Engine ECM. The Engine ECM sends the signal to the VIMS, which informs the operator if the filters are restricted. If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.
NOTE:
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Before climbing the truck ladder, make sure that the ma nual engine shutdown switch (1) is OFF. The engine will not start if the manual shutdown switch is ON. If necessary, the switch can be used to stop the engine from the ground level. Operate the switch periodically to check the secondary steering system. The toggle switches (2) control the lights in the engine compartment and above the access ladder. The RS-232 service connector (3) is used to connect a laptop computer with VIMS PC software to upload new source and configuration files, view real time data or download logged information from the VIMS. The battery disconnect switch (4) and VIMS service connector key switch (5) must be in the ON position before the laptop computer with VIMS software will communicate with the VIMS. The blue service lamp (6) is part of the VIMS. When the key start switch is turned to the ON position, the VIMS runs through a self test. During the self test, the service lamp will flash three times if any logged events are stored in the VIMS main module and once if no logged events are stored. During normal operation, the service lamp will turn ON to notify service personnel that the VIMS has an active data (machine) or maintenance (system) event. The service lamp flashes to indicate when an event is considered abusive to the machine.
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Shown is the 789C truck. While climbing the ladder, make a thorough inspection of the radiator. Be sure that no debris or dirt is trapped in the cores. Check the air filter restriction indicators (1) located on both sides of the truck. If the yellow pistons are in the red zone (indicating that the filters are plugged), the air filters must be serviced. Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. Replace the dust valve if the rubber is not flexible. The VIMS will also provide the operator with an air filter restriction warning when the filter restriction is approximately 6.2 kPa (25 in. of water). Black exhaust smoke is also an indication of air filter restriction. Two filter elements are installed in the filter housings. The large element is the primary element and the small element is the secondary element. Air intake system tips: - The primary element can be cleaned a maximum of six times. - Never clean the secondary element for reuse. Always replace the secondary element. - Air filter restriction causes black exhaust smoke and low power. - A 0.6°C (1°F) increase in intake temperature increases exhaust temperature 1.8°C (3°F). - Exhaust temperature should not exceed 750°C (1382°F).
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Shown is a 789C truck. The capacity of the 789C cooling system has been increased by 40% from 474 Liters (125 gal.) to 663 Liters (175 gal.). The radiator is larger and a shunt tank (1) has been added above the radiator. The cooling system on the "C" Series trucks is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. These two systems are not connected. When servicing the cooling systems, be sure to drain and fill both systems separately. The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the two coolant levels. The water used in the cooling system is critical for good cooling system performance. Use distilled or deionized water whenever possible to prevent acids or scale deposits in the cooling system. Acids and scale deposits result from contaminants that are found in most common water sources. Never use water alone. All water is corrosive at engine operating temperatures without coolant additives. Also, water alone has none of the lubrication properties which are required for water pump seals.
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Text Reference
The "C" Series trucks are filled at the factory with Extended Life Coolant (ELC). If ELC is maintained in the radiator, it is not necessary to use a supplemental coolant additive. If more than 10% of conventional coolant is mixed with the ELC, a supplemental coolant additive is required. With conventional coolant, maintain a 3 to 6% co ncentration of supplemental coolant additive. - Too much additive will form insoluble salts that cause water pump seal wear, plugging and will coat parts with excessive deposits that prevent heat transfer. - Not enough additive will result in severe cavitation erosion which will pit and corrode cylinder liner and block surfaces. Maintain a 30 to 60% concentration of Caterpillar Antifreeze. - More than 60% antifreeze concentration will reduce freeze protection and cause radiator plugging. - Less than 30% antifreeze concentration will result in cavitation erosion, which will pit and corrode cylinder liner and block surfaces and decrease water pump life. - Most commercial antifreezes are formulated with high silicate content for gasoline engines and are not recommended for diesel engines. The engine should operate between 88 and 99°C (190 and 210°F). - Operating below this temperature range will cause overcooling problems. - Operating above this temperature range will cause overheating problems. Cooling system pressure should be between 55 and 110 kPa (8 and 16 psi). - Raising the pressure raises the boiling point. If the pressure is inadequate, the coolant will boil over and the engine will overheat. Do not fill the cooling system faster than 20 L/min. (5 gpm). - Filling the cooling system faster than 20 L/min. (5 gpm) will cause air pockets that could produce damaging steam. Keep the fan belts adjusted. Keep the radiator cooling fins straight and clean.
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Shown is a 785C truck. The air cleaner indicators (1) are located on the filter housings. If the yellow pistons are in the red zone (indicating that the filters are plugged), the air cleaners must be serviced. Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. Replace the dust valve if the rubber is not flexible.
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The ether cylinders (arrow) are located in the engine compartment behind the radiator. Make sure the ether cylinders are not empty. The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch in the cab on the center console (see Visual No. 48). The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1900 rpm. Ether starting tip: - Cold weather causes rough combustion and white exhaust smoke from unburned fuel. Ether injection will reduce the duration and severity of unburned fuel symptoms.
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The batteries are located below the access panel on the right platform. Inspect the battery connections for corrosion or damage. Keep the battery terminals clean and coated with with petroleum jelly. jelly. Inspect the electrolyte level in each battery cell, except for maintenance free batteries. batteries. Maintain the level to the bottom of o f the fill openings with distilled water.
WARNING
Batteries give off flammable fumes that can explode resulting in personal injury. Prevent sparks near batteries. They could cause vapors to explode. Do not allow jumper cable ends to contact each other or the machine. Do not smoke when checking battery electrolyte levels. Electrolyte is an acid and can cause personal injury if it contacts skin or eyes. Always wear eye protection when starting a machine with jumper cables. Always connect the battery positive (+) to battery positive (+) and the battery negative (-) to the stalled machine frame (-).
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Located on the right platform are the automatic lubrication system grease tank (1), the main air system tank (2), and the steering system tank (3). Check the level of the grease in the automatic lubrication system tank with the grease level indicator located on top of the tank. A drain valve is located at the bottom right of the main air system tank. Drain the condensation from the air tank each morning.
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The oil level for the steering system tank is checked at the upper up per sight gauge (1) when the oil is cold and the engine is stopped. After the engine is started, started, the oil level will decrease as the oil fills the steering accumulators. After the accumulators are filled, the oil level should be checked again aga in at the lower sight gauge (2). When the engine is running and the accumulators are fully charged, the oil level should not be below the ENGINE RUNNING RUNNING marking of the lower gauge. If the ENGINE RUNNING level is not correct, check the nitrogen charge in each accumulator. accumulator. A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity capacity.. Before removing the cap to add oil to the steering system, be sure that the engine was shut off o ff with the key start switch, and the steering oil has returned to the tank from the accumulators. Then, depress the pressure release button (3) on the breather to release any remaining pressure from the tank. Also located on the tank are the main steering oil filter (4) and the steering pump case drain filter (5). If the steering pump fails fails or if the engine cannot be started, the connector (6) is used to attach attach an Auxiliary Power Unit (APU). (APU). The APU will provide supply oil from the steering steering tank at the connector (6) to charge the steering steering accumulators. Steering capability is then available to tow the truck.
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Text Reference
INSTRUCTOR NOTE: For more detailed information on servicing the steering accumulators, refer to the Special Instruction "Repair of 4T8719 Bladder Accumulator Group" (Form SEHS8757). For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)"(Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).
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Another small air tank (not visible) is located behind the cab (see Visual Visual No. 178). The air tank behind the cab supplies air to the parking and secondary brakes. Drain the moisture from the tank daily with the drain valve (arrow).
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The windshield washer reservoir (1) is located in the compartment in front of the cab. Keep the reservoir full of windshield washer fluid. The air conditioner filter (2) is also located in the compartment in front of the cab. Clean or replace the filter element when a reduction of circulation in the cab is noticed.
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The remaining 10 Hours or Daily checks are performed in the operator's compartment: - Brakes: Check operation - Indicators and gauges: Test operation - Seat belt: Inspect - Back-up alarm: Test operation - Secondary steering: Test operation The brakes are checked by engaging one of the brake systems and placing the shift lever in FIRST FORWARD. Accelerate the engine until the truck moves. The truck must not move below 1200 rpm. This procedure should be repeated for each brake lever or pedal. The cab fresh air filter is located behind the cover (arrow). Clean or replace the cab fresh air filter when necessary. INSTRUCTOR NOTE: Refer to the Operation and Maintenance Manual for more information on the remaining tests performed in the cab.
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OPERATOR'S STATION
The operator's station for the "C" Series Off-highway Trucks has been changed to improve operator comfort and ergonomics. The "C" Series cab now resembles the cab used on the smaller "D" Series Off-highway Trucks. The VIMS controls the Truck Payload Measurement System (TPMS) on the 785C and 789C trucks. There are two sets of TPMS external loading lamps on the truck. One set of lamps is on the left side of the cab (arrow) and the other set is on the right platform. The lamps are green and red. The lamps inform the loader operator of the loading progress toward a target payload weight (set through the VIMS Keypad). The lamps are active only during the loading cycle and are off at all other times. During loading, the green (continue loading) lamps will be ON until the payload is 95% of the target weight setting. Then, the red (stop loading) lamp will light. A "last pass" indication can be programmed into the system using the VIMS Keypad. With last pass indication, the VIMS calculates an average loader pass size and predicts payload weight. If the predicted weight after the NEXT loader pass will be above 95% of the target weight setting, the red lamps FLASH. The red lamps will be ON continuously after the last pass (when fully loaded). A minimum of three loader passes are required for the "last pass" indication option to function correctly.
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Shown is a view of the operator's seat and the trainer's seat. The seats are more comfortable with improved seat adjustments. The trainer's seat has more leg room and can be replaced with an attachment air suspension seat.
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The "C" Series truck hoist system is electronically controlled. The hoist control lever (arrow) activates the four positions of the hoist control valve. The four positions are: RAISE, HOLD, FLOAT, and LOWER. A fifth position of the hoist valve is called the SNUB position. The operator does not have control over the SNUB position. The body position sensor (see Visual No. 129) controls the SNUB position of the hoist valve. When the body is lowered, just before the body contacts the frame, the Transmission/Chassis ECM signals the hoist solenoids to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent hard contact of the body with the frame. The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist valve will actually be in the SNUB position. If the transmission is in REVERSE when the bod y is being raised, the hoist lever sensor is used to shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until: 1. The hoist lever is moved into the HOLD or FLOAT position; and 2. the shift lever has been cycled into and out of NEUTRAL. If the truck is started with the body raised and the hoist lever in FLOAT, the lever must be moved into HOLD and then FLOAT before the body will lower.
NOTE:
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Shown is an overall view of the dash from the left side of the cab. Some of the improvements are: - Telescopic/tilt steering column for individual adjustment - Intermittent wiper/washer, turn signal control and dimmer switch - Enhanced instrument layout - Backlit rocker switches - Steering wheel mounted electric horn control
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The operator controls to the left of the steering column are: - Telescopic/tilt steering column adjustment lever (1): Push for telescoping and pull for tilt - Intermittent wiper/washer, turn signal control and dimmer switch (2) - Steering wheel mounted electric horn control (3) - Cigarette lighter (4): The cigarette lighter socket receives a 12-Volt power supply. This socket can be used as a power supply for 12-Volt appliances. Another 12-Volt power port is provided behind the operator's seat.
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41
Shown is a closer view of the intermittent wiper/washer, turn signal control and dimmer switch. Windshield washer: Push the button at the end of the lever to activate the electrically powered windshield washer. Intermittent wiper switch (six positions): - OFF (0) - Intermittent position 1 (one bar) - Intermittent position 2 (two bars) - Intermittent position 3 (three bars) - Low speed continuous wiper (I) - High speed continuous wiper (II) Dimmer switch: Pull the lever toward the operator for BRIGHT lights, and push the lever away from the operator for DIM lights. Turn signals: Lift the lever for a RIGHT turn, and lower the lever for a LEFT turn.
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Located on the right side of the steering column is the manual retarder lever. The manual retarder lever is used to modulate engagement of the service brakes on all four wheels. The retarder system allows the machine to maintain a constant speed on long downgrades. The retarder will not apply all of the normal braking capacity. Located on the dash to the right of the retarder lever are (from left to right): - Key start switch - Temperature variable knob - Fan speed switch
NOTICE Do not use the retarder control as a parking brake or to stop the machine.
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Located on the floor of the cab are: - Secondary brake pedal (1): Used to modulate application of the parking brakes on all four wheels. - Service brake pedal (2): Used to modulate engagement of the service brakes on all four wheels. For more precise modulation of the service brakes, use the manual retarder lever on the right side of the steering column. - Throttle pedal (3): A throttle position sensor is attached to the throttle pedal. The throttle position sensor provides the throttle position input signals to the Engine ECM. The throttle position must be programmed to the 10 to 90% setting. The earlier trucks must be programmed to a 10 to 50% throttle position. The setting is changed in the Engine ECM configuration screen with ET.
NOTE:
The Engine ECM provides an elevated engine idle speed of 1300 rpm when the engine coolant temperature is below 60°C (140°F). The rpm is gradually reduced to 1000 rpm between 60°C (140°F) and 71°C (160°F). When the temperature is above 71°C (160°F), the engine will idle at LOW IDLE (700 rpm). Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can release the parking brake or depress the throttle momentarily, and the idle speed will decrease to LOW IDLE for 10 minutes.
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To the right of the operator's seat is the shift console. Located on the shift console are the transmission shift lever (1) and the parking brake air valve (2). The "C" Series truck transmissions have SIX speeds FORWARD and ONE speed REVERSE. The top gear limit and body up gear limit are programmable through the Transmission/Chassis ECM. The top gear limit can be changed from THIRD to SIXTH. The body up gear limit can be changed from FIRST to THIRD.
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Located in the overhead panel are several switches: - Hazard lights (1) - Headlights and parking/taillights (2) - Fog lights (3) - Back-up lights (4) - Front flood/ladder lights (5)
Text Reference
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Shown is the circuit breaker panel located behind the operator's seat. The previous "B" Series trucks used fuses to protect many of the electrical circuits. The "C" Series trucks use only circuit breakers to protect the electrical circuits. A 12-Volt/5 amp power port (1) provides a power supply for 12-Volt appliances, such as a laptop computer. A laptop computer with the VIMS software installed can be connected to the diagnostic connector (2) to obtain diagnostic and production information from the VIMS Electronic Control. A laptop computer with the Electronic Technician (ET) software installed can be conne cted to the CAT Data Link connector (3) to obtain diagnostic information and perform programming functions on all the electronic controls.
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47
Shown is the center of the front dash panel. Eight dash indicators, the four-gauge cluster module, and the speedometer/tachometer module are visible. The four dash indicators to the left of the four-gauge cluster module are (from top to bottom): - Left turn - Body up: Lights when the body is up. Input is from the body position sensor. - Reverse: Lights when the shift lever switch is in REVERSE. - High beam The four dash indicators to the right of the speedometer/tachometer module are (from top to bottom): - Right turn - Action lamp: Lights when a Category 2, 2-S, or Category 3 Warning is active. - Retarder: Lights when the retarder is ENGAGED (Auto or Manual). Flashes rapidly when a fault in the ARC system is detected. - TCS: Lights when the Traction Control System (TCS) is ENGAGED.
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Text Reference
The four systems monitored by the four-gauge cluster module are (top and bottom, left to right): - Engine coolant temperature: Maximum operating temperature is 107°C (225°F). - Brake oil temperature: Maximum operating temperature is 121°C (250°F). - System air pressure: Minimum operating pressure is 450 kPa (65 psi). - Fuel level: Minimum operating levels are 15% (Category 1) and 10% (Category 2). The three systems monitored by the speedometer/tachometer module are: - Tachometer: Displays the engine speed in rpm. - Ground speed: Displayed in the left side of the three-digit display area and can be displayed in miles per hour (mph) or kilometers per hou r (km/h). - Actual gear: Displayed in the right side of the three-digit display area and consists of two digits that show the actual transmission gear that is engaged. The left digit shows the actual gear (such as "1," "2," etc.). The right digit shows the direction selected ("F," "N" or "R").
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48
To the right of the Speedometer/Tachometer Module are several rocker switches. The rocker switches control the following systems: Top row (from left to right) - Throttle back-up: Raises the engine speed to 1300 rpm if the throttle sensor signal is invalid. - Ether starting aid: Allows the operator to manually inject ether if the engine oil temperature is below 10°C (50°F) and engine speed is below 1900 rpm. The manual ether injection duration is five seconds (see Visuals No. 66 and 90). - ARC: Activates the Automatic Retarder Control (ARC) system. - Brake release/hoist pilot: Used to release the parking brakes for towing and provide hoist pilot oil to lower the body with a dead engine. The small latch must be pushed UP before the switch can be pushed DOWN. - TCS test: Tests the Traction Control System (TCS). Use this switch when turning in a tight circle with the engine at LOW IDLE and the transmission in FIRST GEAR. The brakes should ENGAGE and RELEASE repeatedly. The test must be performed while turning in both directions to complete the test. Bottom row (from left to right) - Panel Lights: Use this switch to DIM the panel lights - Air Conditioning: Use this switch to turn ON the air conditioner.
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Shown is the Vital Information Management System (VIMS) message center module (1) and the keypad module (2). The message center module consists of an alert indicator, a universal gauge, and a message display window. The alert indicator flashes when a Category 1, 2, 2-S, or 3 Warning is present. The universal gauge displays active or logged data (machine) and maintenance (system) events. The universal gauge will also display the status of a sensor parameter selected for viewing by depressing the GAUGE key on the keypad. The message display window shows various types of text information to the operator, depending on the menu selected with the keypad. An active event will override most displays until acknowledged by depressing the OK Key.
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Text Reference
The VIMS provides three Warning Categories. The first category requires only operator awareness. The second category states that the operation of the machine and the maintenance procedure of the machine must be changed. The third Warning Category states that the machine must be safely shut down immediately. Warning Category 1
For a Category 1 Warning, the alert indicator will flash. The universal gauge may display the parameter and a message will appear in the message display window. A Category 1 Warning alerts the operator that a machine system requires attention. The "OK" key on the keypad can be used to acknowledge the warning. Some warnings will be silenced for a predetermined period. After this time period, if the abnormal condition is still present, the warning will reappear. Warning Category 2
For a Category 2 Warning, the alert indicator and the action lamp will flash. The universal gauge may display the parameter and a message will appear in the message display window. A Category 2 warning alerts the operator that a change in machine operation is required to avoid possible damage to the indicated system. The "OK" key on the keypad can be used to acknowledge the warning. Some warnings will be silenced for a predetermined period. After this time period, if the abnormal condition is still present, the warning will reappear. Warning Category 2-S
For a Category 2-S Warning, the alert indicator and the action lamp will flash and a continuous action alarm will sound, which indicate a SEVERE Category 2 Warning. The universal gauge may display the parameter and a message will appear in the message display window. A Category 2-S Warning alerts the operator to immediately change the operation of the machine to avoid possible damage to the indicated system. When the change in operation is made to an acceptable condition, the action alarm will turn off. Warning Category 3
For a Category 3 Warning, the alert indicator and the action lamp will flash and the action alarm will sound intermittently. The universal gauge may display the parameter and a message will appear in the message display window. A Category 3 Warning alerts the operator that the machine must be safely shut down immediately to avoid damage to the machine or prevent personal injury. Some Category 3 Warnings cannot be stopped by pressing the "OK" key.
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Gauge Cluster Module
Service Lamp Service Key Start Switch
Vims
VIMS RS-232 Port
Main Module
Speedometer/ Tachometer Module
Text Reference
Message Center Module
Keypad Module
MPH 1 2 km/ h 3F
VIMS Service Tool and Software
Vims Interface Module
Electronic Technician /ECAP Display Data Link
Vims Interface Module
Keypad Data Link CAT Data Link
Engine ECM Action Alarm Action Lamp CAT Data Link Sensors
VITAL INFORMATION MANAGEMENT SYSTEM (VIMS)
Sensors Transmission / Chassis ECM
Brake ECM (ARC /TCS)
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The VIMS uses two interface modules to receive input signals from many switches and sensors located around the machine. The VIMS also communicates with other electronic controls on the machine. The VIMS provides the operator and the service technician with a complete look at the current and past conditions of all the systems on the truck. The Truck Production Management System (TPMS) is an integral part of the VIMS. Access to the TPMS information is provided through the VIMS message center and keypad modules and a laptop computer with the VIMS PC software installed. The VIMS monitors all the systems on the truck, but ET is used for programming, running diagnostic tests and retrieving logged information from the Engine ECM, the Transmission/Chassis ECM, and the Brake ECM (ARC and TCS).
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Shown is the location are the Brake ECM (1) and the Transmission/Chassis ECM (2). The Brake ECM controls the Automatic Retarder Control (ARC) system, the Traction Control System (TCS), and rear axle cooling. The Transmission/Chassis ECM controls the shifting of the transmission, torque converter lockup, the hoist system, the neutral-start feature, power train filter and temperature monitoring, and the automatic lubrication feature. All these electronic controls, along with the Engine ECM, communicate with each other on the CAT Data Link. All the information from these controls can be accessed through the VIMS message center or a laptop computer with Electronic Technician (ET) or VIMS PC software.
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Shown is a laptop computer with the VIMS PC diagnostic software installed. The laptop computer is connected to the VIMS diagnostic connector. Some of the operations that can be performed with a laptop computer with VIMS PC installed are: - View real time data (similar to the status menu of ET) - View payload data - Start and stop a data logger - Calibrate the payload system - Upload source and configuration files (similar to flash programming other ECM’s with ET) - Assign serial and equipment numbers - Reset onboard date, time, and hourmeter - Download event list, data logger, event recorder, payload data, trend data, cumulative data, and histogram data INSTRUCTOR NOTE: For more detailed information on the VIMS, refer to the Service Manual Modules "Off-Highway Truck/Tractors Vital Information Management System (VIMS)--System Operation" (Form RENR2630) and "Off-Highway Truck/Tractors Vital Information Management System (VIMS)--Testing and Adjusting Troubleshooting" (Form RENR2631).
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Shown is the 7X1700 Communication Adapter and a laptop computer with the Electronic Technician (ET) diagnostic software installed. The communication adapter is connected to the CAT Data Link diagnostic connector located on the circuit breaker panel. The electronic controls (Transmission/Chassis ECM and Brake ECM) used on the "C" Series trucks no longer have diagnostic windows to access diagnostic information. To perform diagnostic and programming functions with these electronic controls, the service technician must use a laptop computer with ET.
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ENGINE
Shown is the 3516B engine used in the 789C Off-highway Truck. The 789C is equipped with the Caterpillar 3516B quad turbocharged and aftercooled engine. The 785C is equipped with the Caterpillar 3512B twin turbocharged and aftercooled engine. The 785C and 789C engines have increased horsepower. The engine power ratings for the 785C and 789C trucks are: 785C: gross power--1082 kW (1450 hp) net power--1007 kW (1350 flywheel hp) 789C: gross power--1417 kW (1900 hp) net power--1335 kW (1790 flywheel hp)
These engines utilize the Electronic Unit Injection (EUI) system for power, reliability and economy with reduced sound levels and low emissions.
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Text Reference
3500B ELECTRONIC CONTROL SYSTEM COMPONENT DIAGRAM
Engine ECM
Ground Bolt
Electronic Unit Injectors
15 Amp Breaker
Throttle
Disconnect Switch Main Power Relay
Key Start Switch
24 V
Timing Probe Connector
Engine Coolant Temperature Rear Aftercooler Temperature
Oil Level Switch (Low)
Speed /Timing Sensor Engine Oil Pressure (Unfiltered)
Engine Oil Pressure (Filtered)
Ether Solenoid
Atmospheric Pressure
Manual Ether Switch
Throttle Override Switch
Turbo Outlet Pressure (Boost) Ground Level Shutdown Switch
Right Turbo Inlet Pressure
Fuel Filter Switch
Left Turbo Inlet Pressure
Service Tool Transmission /Chassis ECM
Crankcase Pressure
Right Turbo Exhaust Left Turbo Exhaust
Brake ECM Vims
Engine Oil Renewal Solenoid
Shutter Solenoid
Fan Clutch Solenoid Fan
CAT Data Link
A/C Pressure Switch
Pre-lubrication Relay Coolant Flow Switch
Fan Speed Sensor
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Engine Electronic Control System
Shown is the electronic control system component diagram for the 3500B engines used in the "C" Series trucks. Fuel injection is controlled by the Engine Electronic Control Module (ECM). Many electronic signals are sent to the Engine ECM by sensors, switches, and senders. The Engine ECM analyzes these signals and determines when and for how long to energize the injector solenoids. When the injector solenoids are energized determines the timing of the engine. How long the solenoids are energized determines the engine speed.
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Text Reference
"Pull-up voltage" is a voltage supplied from within an ECM through an internal resister which "pulls up" the signal circuit contact on the connector of the control input. Pull-up circuits are used on most sensor and switch inputs of electronic controls. Frequency sensors do not receive a pull-up voltage (except for suspension cylinder pressure sensors). The pull-up voltage is determined by the ECM design and will vary between ECMs. Pull-up voltage sometimes is the same value as the voltage source that powers the sensor, but does not have to be. Remember, pull-up voltage is on the SIGNAL input to the ECM for a given sensor (or switch) and most often HAS NO relationship to the voltage that POWERS the sensor. PWM sensors most often have a pull-up voltage value DIFFERENT than the voltage that powers them. Analog sensors, as used with the engine ECM, most often have a pull-up voltage that is the SAME as the voltage that powers them. The Engine ECM will provide a "pull-up voltage" to the signal circuit of the sensors when the ECM senses an OPEN circuit. The signal circuit is pin C of the 3-pin sensor connectors. The pull-up voltage for the Engine ECM sensors is approximately 6.50 volts. To test for pull-up voltage, use a digital multimeter set to DC voltage, and use the following procedure (key start switch must be ON): 1. Measure between pins B (analog or digital return) and C (signal) on the ECM side of a sensor connector before it is disconnected. The voltage that is associated with the current temperature or pressure should be shown. 2. Disconnect the sensor connector while still measuring the voltage between pins B and C. If the circuit between the ECM and the sensor connector is good, the multimeter will display the pull-up voltage.
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Text Reference
56
Fuel injection and some other systems are controlled by the Engine ECM (arrow) located on top of the engine. Other systems controlled by the Engine ECM include: - Ether injection
- Engine start function
- Engine oil pre-lubrication
- Variable speed fan control
The Engine ECM has two 40-pin connectors. The connectors are identified as "J1" and "J2." Be sure to identify which connector is the J1 or J2 connector before performing diagnostic tests. The Engine ECM is cooled by fuel. Fuel flows from the fuel transfer pump through the ECM to the secondary fuel filters. Occasionally, Caterpillar will make changes to the internal software (personality module) that controls the performance of the engine. These changes can be performed by physically installing a new personality module, located below the ECM, or by using the WinFlash program that is part of the laptop software program, Electronic Technician (ET). ET is used to diagnose and program the electronic controls used in Off-highway Trucks. If using the WinFlash program, a "flash" file must be obtained from Caterpillar and uploaded into the existing ECM personality module. The ECM in earlier 3500 engines had one 70-pin connector and cannot be reprogrammed with the WinFlash application in ET. Reprogramming of the earlier ECM requires a replacement of the personality module located behind an access cover on the ECM.
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A timing calibration connector is located next to the ECM. If the engine requires timing calibration, a timing calibration sensor (magnetic pickup) is installed in the flywheel housing and connected to the timing calibration connector. Using the Caterpillar ET service tool, timing calibration is performed automatically for the speed/timing sensors. The desired engine speed is set to 800 rpm. This step is performed to avoid instability and ensures that no backlash is present in the timing gears during the calibration process. Timing calibration improves fuel injection accuracy by correcting for any slight tolerances between the crankshaft, timing gears, and timing wheel. Timing calibration is normally performed after the following procedures: 1. ECM replacement 2. Speed/timing sensor replacement 3. Timing wheel replacement
INSTRUCTOR NOTE: Some of the engine electronic control system input components are shown during the discussion of other systems. See the following visual numbers: 23. 25. 46. 48. 48. 62. 63. 68. 68. 68. 74. 78. 81. 86. 90. 92.
Engine oil level switch Engine shutdown switch CAT Data Link connector Throttle back-up switch Manual ether switch Air conditioner compressor pressure switch Engine crankcase pressure sensor Coolant temperature sensor Turbocharger outlet pressure sensor Engine fan speed sensor Coolant flow switch Rear aftercooler temperature sensor Engine oil pressure and filter restriction sensors Fuel filter restriction switch Turbocharger inlet pressure sensor Turbocharger temperature sensor
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57
The atmospheric pressure sensor (arrow) is located adjacent to the Engine ECM. The Engine ECM uses the atmospheric pressure sensor as a reference for calculating boost and air filter restriction. The sensor is also used for derating the engine at high altitudes. The ECM will derate the engine at a rate of 1% per kPa to a maximum of 20%. Derating begins at a specific elevation. The elevation specification can be found in the Technical Marketing Information (TMI) located on the Caterpillar Network. If the Engine ECM detects an atmospheric pressure sensor fault, the ECM will derate the fuel delivery to 20%. If the Engine ECM detects an atmospheric and turbocharger inlet pressure sensor fault at the same time, the ECM will de rate the engine to the maximum rate of 40%. The Engine ECM also uses the atmospheric pressure sensor as a reference when calibrating all the pressure sensors. The atmospheric pressure sensor is one of the many analog sensors that receive a regulated 5.0 ± 0.5 Volts from the Engine ECM. The atmospheric pressure sensor output signal is a DC Voltage output signal that varies between 0.2 and 4.8 Volts DC with an operating pressure range between 0 and 111 kPa (0 and 15.7 psi). To check the output signal of analog sensors, connect a multimeter between Pins B and C of the sensor connector. Set the meter to read "DC Volts." The DC Voltage output of the atmospheric pressure sensor should be between 0.2 and 4.8 Volts DC.
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1
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The engine speed/timing sensor (1) is positioned near the rear of the left camshaft. The sensor signals the speed, direction, and position of the camshaft by counting the teeth and measuring the gaps between the teeth on the timing wheel which is mounted on the camshaft. The engine speed/timing sensor is one of the most important inputs to the Engine ECM. If the Engine ECM does not receive an input signal from the engine speed/timing sensor, the engine will not run. The engine speed/timing sensor receives a regulated 12.5 ± 1.0 Volts from the Engine ECM. To check the output signal of the speed/timing sensor, connect a multimeter between Pins B and C of the speed/timing sensor connector. Set the meter to read "Frequency." The frequency output of the speed/timing sensor should be approximately: - Cranking: 23 to 40 Hz - Low Idle: 140 Hz - High Idle: 385 Hz A passive (two wire) engine speed sensor (2) is positioned on top of the flywheel housing. The passive speed sensor uses the passing teeth of the flywheel to provide a frequency output. The passive speed sensor sends the engine speed signal to the Transmission/Chassis ECM and the Brake ECM.
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The signal from the passive speed sensor is used for several purposes: - Automatic Retarder Control (ARC) engine control speed - Shift time calculations - Transmission Output Speed (TOS) ratification The output signal of the passive speed sensor can also be checked by connecting a multimeter between the two pins of the speed sensor connector and setting the meter to read frequency. Turn ON the engine shutdown switch (see Visual No. 25) during the cranking test to prevent the engine from starting. The cranking speed and frequency output will vary depending on weather and machine conditions. When viewing engine speed in the ET status screen, cranking speed should be between 100 and 25 0 rpm. NOTE:
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59
The throttle position sensor (arrow) provides the desired throttle position to the Engine ECM. If the Engine ECM detects a fault in the throttle position sensor, the throttle back-up switch (see Visual No. 48) can be used to increase the engine speed to 1300 rpm. The throttle position sensor receives a regulated 8.0 ± 0.5 Volts from the Engine ECM. The throttle position sensor output signal is a Pulse Width Modulated (PWM) signal that varies with throttle position and is expressed as a percentage between 0 and 100%. To check the output signal of the throttle position sensor, connect a multimeter between Pins B and C of the throttle position sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the throttle position sensor should be: - Low Idle: 16 ± 6% - High Idle: 85 ± 4% The throttle position must be programmed to the 10 to 90% setting. The earlier trucks must be programmed to a 10 to 50% throttle position. The setting is changed in the Engine ECM configuration screen with ET.
NOTE:
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Shown is the top of a cylinder head with the valve cover removed. The most important output from the Engine ECM is the Electronic Unit Injection (EUI) injector solenoid (arrow). One injector is located in each cylinder head. The engine control analyzes all the inputs and sends a signal to the injector solenoid to control engine timing and speed. Engine timing is determined by controlling the start and end time that the injector solenoid is energized. Engine speed is determined by controlling the duration that the injector solenoid is energized. 3500B injectors are calibrated during manufacturing for precise injection timing and fuel discharge. After the calibration, a four-digit "E-trim" code number is etched on the injector tappet surface. The E-trim code identifies the injector's performance range. When the injectors are installed into an engine, the trim code number of each injector is entered into the personality module (software) of the Engine ECM using the ECAP or ET service tool. The software uses the trim code to compensate for the manufacturing variations in the injectors and allows each injector to perform as a nominal injector. When an injector is serviced, the new injector's trim code should be programmed into the Engine ECM. If the new trim code is not entered, the previous injector's characteristics are used. The engine will not be harmed if the new code is not entered, but the engine will not provide peak performance.
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3500B IMPROVEMENTS INPUT SWITCHES AND SENSORS - Coolant Flow - Rear Aftercooler Temperature - Engine Oil Level - Turbocharger Temperature - Engine Oil Filter Pressure / Restriction - Engine Fan Speed - Fuel Filter Restriction - Air Conditioner Compressor Pressure - Crankcase Pressure 61
The 3500B engines have many improvements over the original 3500 engines. Some of the improvements are accomplished by adding additional switch and sensor inputs to the Engine ECM. Adding additional inputs allows the ECM to control the engine more precisely. Additional inputs to the 3500B ECM are: - Coolant flow is monitored (see Visual No. 74). - Rear aftercooler temperature is measured (see Visual No. 78). - Engine oil level is monitored (see Visual No. 23). - Two turbocharger temperature sensors measure exhaust temperatures (see Visual No. 92). - Two engine oil pressure sensors are located on the oil filter base to measure oil pressure and oil filter restriction (see Visual No. 81. - Engine fan speed is measured (with variable fan speed attachment). - Fuel filter restriction is monitored (see Visual No. 86). - Air conditioner compressor pressure is monitored (for variable fan speed control) (see Visual No. 62). - Engine crankcase pressure is measured (see Visual No. 63).
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An air conditioner compressor switch (arrow) is located at the rear of the air conditioner compressor. If the truck is equipped with the variable fan speed attachment, the air conditioner compressor switch signals the Engine ECM when the air conditioner system is ON. When the air conditioner system is ON, the ECM sets the v ariable speed fan at MAXIMUM rpm. Disconnecting the air conditioner compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm.
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The crankcase pressure sensor (arrow) is located on the right side of the engine above the engine oil cooler. The crankcase pressure sensor provides an input signal to the Engine ECM. The ECM provides the signal to the VIMS, which informs the operator of the crankcase pressure. High crankcase pressure may be caused by worn piston rings or cylinder liners. If crankcase pressure exceeds 3.6 kPa (.5 psi) or 14.4 inches of water, a high crankcase pressure event will be logged. No factory password is required to clear this event.
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3500B IMPROVEMENTS PREVIOUS LOGGED EVENTS - Air Filter Restriction - Low Oil Pressure - High Coolant Temperature - Engine Overspeed
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The 3500B ECM logs the four events of the previous 3500 engine plus some additional events. The four events logged by the 3500 ECM and the 3500B ECM are: Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum derate of 20%.
If the atmospheric and turbo inlet pressure sensors both fail at the same time, a derate of 40% will occur. Low oil pressure: From less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE. High coolant temperature: Greater than 107°C (226°F). Engine overspeed: Greater than 2200 rpm.
NOTE:
Factory passwords are are required required to clear all the events listed above.
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3500B IMPROVEMENTS ADDITIONAL LOGGED EVENTS - Oil Filter Restriction
- Low Coolant Flow
- Fuel Filter Restriction
- User Defined Shutdown
- High Exhaust Temperature
- Low Boost Pressure
- Hig High h Aft After erco cool oler er Temp Temper erat atur ure e
- Hig High h Boo Boost st Pres Pressu sure re
- Engine Oil Level Low
- Pre-lube Override
- High Crankcase Pressure
65
Additional events logged by the 3500B ECM are: Oil filter restriction: Greater than 70 kPa (10 psi), no factory password required. Greater than 200 kPa (29 psi), factory password required. Fuel filter restriction: Greater than 138 kPa (20 psi). No factory password password required.
than 750°C (1382°F). Maximum derate of 20%. Factory Exhaust temperature high: Greater than password required. Aftercooler coolant temperature high: Greater than 107°C (226°F). Factory password required. Engine oil level low: No factory password required.
water. No factory Crankcase pressure high: Greater than 3.6 kPa (.5 psi) or 14.4 inches of water. password required.
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Coolant flow low: Factory password required. User defined shutdown: The customer has the option of installing systems (fire suppression) that will shut down the the engine if desired. If the installed system system sends a ground signal to the Engine ECM at Connector J1 Pin 19, a user defined shutdown will occur. Factory password password required.
The VIMS will shut down the engine eng ine for any of the following conditions: cond itions: - Eng Engine ine oil oil level level low low - Engine oil press pressure ure low low - Engine coolant temper temperature ature high high - Engine coolant level low - After Aftercooler cooler coolant level low low The engine will only shutdown when ground speed is 0 and the parking brake is ENGAGED. The Engine ECM does not no t log events for VIMS initiated engine shutdowns. Pre-lube override: Override the engine oil pre-lubrication system with the key start switch. Factory password required. (see Visual Visual No. 67)
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3500B IMPROVEMENTS SYSTEMS CONTROLLED BY ECM - Ether Injection - Radiator Shutter Control - Cold Mode - Cold Cylinder Cutout - Engine Start Function - Engine Oil Pre-lubrication - Variable Speed Fan Control - Engine Oil Renewal System
66
The Engine ECM also regulates other systems by energizing solenoids or relays. Some of the other systems controlled by the ECM are: Ether Injection: The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch switch in the cab on the center console (see (see Visual Visual No. 48). The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1900 rpm. Radiator Shutter Control (attachment): On trucks that operate in cold weather, shutters can be added in front of the radiator. Installing shutters in front of the radiator allows the engine to warm up to operating temperature quicker. If a truck is equipped with the attachment radiator shutter control, the shutters are controlled by the En gine ECM.
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Cool Engine Elevated Idle: The Engine ECM provides an elevated engine idle speed of 1300 rpm when the engine coolant temperature is below 60°C (140°F). The rpm is gradually reduced to 1000 rpm between 60°C (140°F) and 71°C (160°F). When the temperature is greater than 71°C (160°F), the engine will operate at low idle (700 rpm).
Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can release the parking brake or depress the throttle momentarily, momentarily, and the idle speed will decrease to LOW IDLE for 10 minutes. Cold Cylinder Cutout: The 3500B engine uses a cold cylinder cutout function to:
- Reduce white exhaust smoke smoke (unburned fuel) after start-up and during extended idling in cold weather - Minim Minimize ize the time time in Cold Cold Mode Mode - Reduce the the use of ether injecti injection. on. After the engine is started and the automatic ether injection system has stopped injecting ether, the Engine ECM will cut out one cylinder at a time to determine which cylinders are firing. firing. The ECM will disable some of the cylinders that are not firing. The ECM can identify a cylinder which is not firing by monitoring the fuel rate and engine speed during a cylinder cutout. The ECM averages the fuel delivery and analyzes the fuel rate change during a cylinder cutout to determine if the cylinder is firing. Disabling some of the cylinders during Cold Mode operation will cause the engine to run rough until the coolant temperature increases above the Cold Mode temperature. This condition is normal, but the operator should be aware it exists to prevent unnecessary complaints. Engine Start Function: The Engine Start function is controlled by the Engine ECM and the Transmission/Chassis Transmiss ion/Chassis ECM. The Engine ECM provides signals to the Transmission/Chassis Transmission/Chassis ECM regarding the engine speed and the condition of the engine pre-lubrication system. The Transmission/Chassis Transmiss ion/Chassis ECM will energize the starter relay only when:
- The shift lever is in NEUTRAL. - The parking brake is ENGAGED. - The engine speed is zero rpm. - The engine pre-lubrication cycle is complete or turned OFF. To protect the starter, starter, the starter is disengaged d isengaged when the engine rpm is above 300 rpm.
NOTE:
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Engine Oil Pre-lubrication (attachment): Engine oil pre-lubrication is controlled by the Engine ECM and Transmission/Chassis ECM. The Engine ECM energizes the pre-lubrication pump relay located behind the cab (see Visual No. 53) The relay behind the cab then energizes the pre-lube relay (1) on the front engine mount. The Engine ECM signals the Transmission/Chassis ECM to crank the engine when: - Engine oil pressure is 3 kPa (.4 psi) or higher. - The pre-lubrication pump (2) has run for 17 seconds. (If the system times out after 17 seconds, a pre-lubrication time out fault is logged in the Engine ECM.) - The engine has been running in the last two minutes. - Coolant temperature is above 50°C (122°F). The engine oil pre-lubrication system can be bypassed to allow quick starts. To override the prelubrication system, turn the key start switch to the CRANK position for a minimum of two seconds. The Transmission/Chassis ECM will begin the pre-lube cycle. While the pre-lube cycle is active, turn the key start switch to the OFF position. Within 10 seconds, turn the key start switch back to the CRANK position. The Transmission/Chassis ECM will energize the starter relay. If the engine oil pre-lubrication system is bypassed using the above procedure, the Engine ECM will log a pre-lube override event that requires a factory password to clear. The ECAP and ET can enable or disable the pre-lubrication feature in the Engine ECM. NOTE:
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Variable Speed Fan Control (attachment): If the engine is equipped with a variable speed fan, the Engine ECM regulates the fan speed. Fan speed varies according to the temperature of the engine. The ECM sends a signal to the variable speed fan control solenoid valve (1) and engine oil pressure engages a clutch as needed to change the speed of the fan. The jacket water coolant temperature sensor (2) is located in the jacket water temperature regulator (thermostat) housing. The ECM uses the coolant temperature sensor information as the main parameter to control the fan speed. The aftercooler temperature sensor, air conditioner pressure sensor and brake cooling oil temperature sensors are also used as inputs to determine the required fan speed. A speed sensor (not shown) is located behind the fan pulley and informs the ECM of the current fan speed. The variable speed fan feature can be turned off using the ECAP or ET service tool. Turning off the variable speed fan feature will set the fan speed at MAXIMUM rpm. Disconnecting the air conditioning compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm (see Visual No. 62). The turbocharger outlet pressure sensor (3) sends an input signal to the Engine ECM. The ECM compares the value of the turbo outlet pressure sensor with the value of the atmospheric pressure sensor and calculates boost pressure. INSTRUCTOR NOTE: For more information on the variable speed fan, refer to the Service Manual "Variable Speed Fan Clutch" (Form SENR8603).
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Engine Oil Renewal System (attachment): Located on the right side of the engine are the components of the engine oil renewal system. Engine oil flows from the engine block through an oil filter (1) to the engine oil renewal solenoid valve (2). When the solenoid is energized and de-energized, a small amount of oil flows from the e ngine oil renewal solenoid valve into the fuel line that returns to the fuel tank. The engine oil mixes with the fuel in the tank and flows with the fuel to the EUI injectors to be burned.
If the machine is equipped with the engine oil renewal system, the engine oil filters, the engine oil renewal system filter, the primary fuel filter, and the secondary fuel filters must all be changed at 500 hour intervals. The engine oil should be changed at least once per year or 4000 service meter hours. Engine oil samples must be taken regularly to ensure that the soot level of the engine oil is in a safe operating range.
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The Engine ECM regulates the amount of oil that is injected by the engine oil renewal solenoid valve. Several parameters must be met before the ECM will allow the injection of oil through the engine oil renewal system. The parameters that must be met are: - Fuel position is greater than 10. - Engine rpm is between 1100 and 1850 rpm. - Jacket water temperature is between 63°C (145°F) and 107°C (225°F). - Oil filter differential pressure at high idle with warm oil is less than 70 kPa (10 psi). - Fuel filter differential pressure is less than 140 kPa (20 psi). - Fuel level is greater than 10%. - Engine oil level switches are sending a valid signal to the Engine ECM. - Engine has been running more than five minutes. The engine oil renewal system can be turned ON or OFF with the ET service tool. The amount of oil injected can also be adjusted by programming the Engine ECM with the ET service tool. The factory setting shown in the service tool is "0" and is equivalent to a 0.5% oil to fuel ratio. The ratio can be changed with the service tool from minus 50 (-50) to plus 50 (+50), which is equivalent to 0.25% to 0.75% oil to fuel ratios. INSTRUCTOR NOTE: For more detailed information on servicing the oil renewal system, refer to the Service Manual Module "Oil Renewal System" (Form RENR2223).
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OIL RENEWAL SOLENOID VALVE Piston
Piston
ON
OFF To Fuel Return
To Fuel Return
From Engine Oil Gallery
From Engine Oil Gallery
70
Shown is a sectional view of the engine oil renewal solenoid valve. When the Engine Slave ECM determines that oil can be injected into the fuel return line, a Pulse Width Modulated (PWM) duty cycle signal is sent to the oil renewal solenoid. The solenoid is turned ON for 1.25 seconds and turned OFF for 1.25 seconds for a total cycle time of 2.5 seconds. How many times the solenoid is turned ON and OFF will determine the volume of oil that is injected. Oil is injected when the solenoid is turned ON and oil is also injected when the solenoid is turned OFF. When the solenoid is turned ON, engine oil flows to the left side of the piston and pushes the piston to the right. The volume of oil that is trapped between the right side of the piston and the check ball compresses the spring and opens the passage to the fuel return line. When the solenoid is turned OFF, engine oil flows to the right side of the piston and pushes the piston to the left. The volume of oil that is trapped between the left side of the piston and the check ball compresses the spring and opens the passage to the fuel return line. The volume of delivery is equal to 3.04 ml/cycle (0.1 oz/cycle).
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4
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Cooling System
Shown is a 789C truck. The capacity of the 789C cooling system has been increased by 40% from 474 Liters (125 gal.) to 663 Liters (175 gal.). The radiator is larger and a shunt tank (1) has been added above the radiator. The shunt tank provides a positive pressure at the coolant pump inlets to prevent cavitation during high flow conditions. The cooling system is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. The only connection between these two systems is a small hole in the separator plate in the shunt tank. The small hole in the shunt tank prevents a reduction of coolant from either of the two systems if leakage occurs in one of the separator plates in the radiator top or bottom tank. When servicing the cooling systems, be sure to drain and fill both systems separately. The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the coolant level. A coolant level switch (3) is located on each side of the shunt tank to monitor the coolant level of both cooling systems (guard removed for viewing switch). The coolant level switches provide input signals to the VIMS, which informs the operator of the engine coolant levels. The jacket water and the aftercooler cooling systems each have their own relief valve (4). If a cooling system overheats or if coolant is leaking from a relief valve, clean or replace the relief valve.
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Shown is the radiator on an earlier 785C. The earlier 785C did not have a shunt tank. The coolant levels are checked at the radiator top tank. Use the gauges (1) on the top tank to check the coolant level. Two coolant level switches (2) are located on the top tank to monitor the coolant level of both cooling systems. The coolant level switches provide input signals to the VIMS, which informs the operator of the engine coolant levels. Pressure relief valves (3) prevent the cooling systems from becoming over pressurized. The jacket water cooling system uses the cores on the right side of the radiator (approximately 60% of the total capacity). The jacket water cooling system temperature is controlled by temperature regulators (thermostats). The aftercooler cooling system uses the cores on the left side of the radiator (approximately 4 0% of the total capacity). The aftercooler cooling system does not have thermostats in the circuit. The coolant flows through the radiator at all times to keep the turbocharged inlet a ir cool for increased horsepower.
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The jacket water pump (1) is located on the right side of the engine. The pump draws coolant from the bypass tube (2) until the temperature regulators (thermostats) open. The thermostats are located in the housing (3) at the top of the bypass tube. When the thermostats are open, coolant flows through the radiator to the water pump inlet. If the jacket water cooling system temperature increases a bove 107°C (226°F), the Engine ECM will log an event that requires a factory password to clear.
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Coolant flows from the jacket water pump, past the coolant flow warning switch (1), and through the various system oil coolers (engine, torque converter/transmission and rear brake). The coolant flow switch sends an input signal to the Engine ECM. The Engine ECM provides the input signal to the VIMS, which informs the operator of the coolant flow status. If the ECM detects a low coolant flow condition, a low coolant flow event will be logged. A factory password is required to clear this event. Jacket water coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap (2).
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Shown is the right side of the engine. The engine oil cooler (1) and the rear brake oil coolers (2) are visible in this view. Jacket water coolant flows through these coolers and through the tube (3) to the transmission oil cooler. Jacket water coolant flows through the transmission oil cooler, the engine oil cooler and the rear brake oil coolers to both sides of the engine cylinder block. Coolant flows through the engine block and through the cylinder heads. From the cylinder heads, the coolant flows to the temperature regulators and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant).
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JACKET WATER COOLANT FLOW
Text Reference
Thermostat Housing
Shunt Tank
Engine Block
Engine Oil Cooler Hoist, Converter and Brake Oil Cooler Hoist, Converter and Brake Oil Cooler Transmission Oil Cooler
Radiator Jacket Water Pump
76
Shown is the jacket water cooling circuit. Coolant flows from the jacket water pump through the coolers to the engine block. Coolant flows through the engine block and the cylinder heads. From the cylinder heads, the coolant flows to the temperature regulators (thermostats) and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant). The shunt tank (789C only) increases the cooling capacity and provides a positive pressure at the coolant pump inlet to prevent cavitation during high flow conditions. In this illustration and those that follow, the colors used to identify the various pressures in the systems are: Red Green Red and White Stripes Brown Orange Blue Yellow Purple
- Supply oil/water pressure - Drain or tank oil/water - Reduced supply oil pressure - Lubrication or cooling pressure - Pilot or load sensing signal pressure - Blocked oil - Moving components - Air pressure
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The auxiliary (aftercooler) water pump (1) for the aftercooler c ooling system is located on the left side of the engine. Coolant enters the aftercooler water pump from the radiator or the shunt tank supply tube (2) on the 789C truck. Coolant flows from the pump to the aftercooler cores through the large tube (3) Aftercooler coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap (not shown) located on the pump.
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Located in a tube at the rear of the aftercooler is the rear aftercooler temperature sensor (1). The rear aftercooler temperature sensor provides an input signal to the Engine ECM. The Engine ECM uses the rear aftercooler temperature sensor signal with the jacket water temperature sensor signal, the brake temperature sensor signals (four) and the air conditioner compressor pressure signal to control the variable speed fan attachment. The Engine ECM also provides the input signal to the VIMS, which informs the operator of the aftercooler coolant temperature. If the rear aftercooler temperature increases above 107°C (226°F), the Engine ECM will log an event that requires a factory password to clear. Coolant flows through the aftercooler cores to the front brake oil cooler (2) located at the rear of the engine. Coolant flows through the front brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling system does not have temperature regulators (thermostats) in the circuit. When the service or retarder brakes are ENGAGED, the front brake oil cooler diverter valve (3) allows brake cooling oil to flow through the front brake oil cooler. Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).
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AFTERCOOLER COOLANT FLOW
Shunt Tank
Front Brake Oil Cooler
Aftercooler
Diverter Valve
Air Compressor
Radiator Aftercooler Water Pump
79
Shown is the aftercooler cooling circuit. Coolant flows from the aftercooler water pump through the aftercooler. Coolant flows through the aftercooler core to the front brake oil cooler located at the rear of the engine. Coolant then flows through the front brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling circuit does not have temperature regulators (thermostats) in the circuit. The shunt tank increases the cooling capacity and provides a positive pressure at the aftercooler water pump inlet to prevent cavitation during high flow conditions. The earlier 785C truck does not have a shunt tank.
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Lubrication System
Shown is the 3512B engine used in the 785C truck. The engine oil pump is located behind the jacket water pump on the right side of the engine. The pump draws oil from the oil pan through a screen. The relief valve (1) for the lubrication system is located on the pump. The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump. Oil flows from the pump through an engine oil cooler bypass valve (2) to the engine oil cooler (3). The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged. On the 3512B engine used in the 785C truck, engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4).
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4
2
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Oil flows from the engine oil cooler to the oil filters on the left side of the engine. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers. Engine oil is added at the fill tube (1) and checked with the dipstick (2). A bypass valve for each filter is located in each oil filter base. Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3) (789C only). (See Visual No. 80 for the 785C S•O•S tap location.) The engine has two oil pressure sensors. One sensor is located on each end of the oil filter base. The front sensor measures engine oil pressure before the filters. The rear sensor (4) measures oil pressure after the filters. The sensors send input signals to the Engine ECM. The ECM provides the input signal to the VIMS, which informs the operator of the engine oil pressure. Used together, the two engine oil pressure sensors inform the operator if the engine oil filters are restricted. If the engine oil pressure is less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE, the Engine ECM will log an event that requires a factory password to clear. If the oil filter restriction exceeds 70 kPa (10 psi), a low oil filter restriction event will be logged. No factory password is required to clear this event. If the oil filter restriction exceeds 200 kPa (29 psi), a high oil filter restriction event will be logged. A factory password is required to clear this event.
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Text Reference
82
Shown is the 3512B engine used in the 785C truck. The 3512B engine uses three oil filters located on the left side of the engine. The 3512B engine also has a fitting (arrow) that can be used to drain the engine oil trapped above the filters. Do not add oil through the fitting (arrow) because unfiltered oil will enter the engine. Any contamination could cause damage to the engine.
NOTICE When changing the engine oil filters, drain the engine oil trapped above the oil filters through the fitting (arrow) to prevent spilling the oil. Oil added to the engine through the fitting will go directly to the main oil galleries without going through the engine oil filters. Adding oil to the engine through the fitting may introduce contaminants into the system and cause damage to the engine.
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Text Reference
ENGINE OIL SYSTEM
Engine Oil Renewal System Solenoid
Scavenge Pump
To Fuel Tank Bypass Valve Engine Oil Filters
Engine Oil Cooler Engine Oil Pump
83
The engine oil pump draws oil from the oil pan through a screen. The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump. Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler. The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged. Oil flows from the engine oil cooler to the oil filters. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers. Some trucks are equipped with an engine oil renewal system. Engine oil flows from the engine block through an oil filter to an engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel (see Visuals No. 69 and 70).
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Text Reference
1
2
84
Fuel System
The fuel tank is located on the left side of the truck. Fuel is pulled from the tank through the fuel heater (not shown), if equipped, and through the primary fuel filter (1) by the fuel transfer pump located on the right side of the engine behind the engine oil pump. A fuel level sensor (2) is also located on the fuel tank. The fuel level sensor emits an ultrasonic signal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonic signal to return is converted to a Pulse Width Modulated (PWM) signal. The PWM signal changes as the fuel level changes. The fuel level sensor provides the input signals to the VIMS, which informs the operator of the fuel level. A category level 1 warning (FUEL LVL LO) is shown on the VIMS display if the fuel level is less than 15%. A category level 2 warning (FUEL LVL LO ADD FUEL NOW) is shown on the VIMS display if the fuel level is less than 10%. The fuel level sensor receives 24 Volts from the VIMS. To check the supply voltage of the sensor, connect a multimeter between Pins 1 and 2 of the sensor connector. Set the meter to read "DC Volts." The fuel level sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the fuel level. To check the output signal of the fuel level sensor, connect a multimeter between Pins 2 and 4 of the fuel level sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depth and 84% at 2000 mm (78.8 in.) of fuel depth.
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Text Reference
1
2
85
Fuel flows from the transfer pump (1) through the Engine ECM to the secondary fuel filters located on the left side of the engine. The fuel transfer pump contains a bypass valve (2) to protect the fuel system components from excessive pressure. The bypass valve setting is 860 kPa (125 psi), which is higher than the setting of the fuel pressure regulator.
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Text Reference
1
2
86
The secondary fuel filters and the fuel priming pump (1) are located above the engine oil filters on the left side of the engine. The fuel priming pump is used to fill the filters after they are changed. Fuel filter restriction is monitored with a fuel filter bypass switch (2) located on the fuel filter base. The fuel filter bypass switch provides an input signal to the Engine ECM. The ECM provides a signal to the VIMS, which informs the operator if the secondary fuel filters are restricted. If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event is logged. No factory password is required to clear this event. Fuel flows from the fuel filter base through the Electronic Unit Injection (EUI) fuel injectors (see Visual No. 60), the fuel pressure regulator, and then returns to the fuel tank. The injectors receive 4 1/2 times the amount of fuel needed for injection. The extra fuel is used for cooling. If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.
NOTE:
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Text Reference
2
1
87
Fuel flows from the fuel filter base through the steel tubes (1) to the EUI fuel injectors. Return fuel from the injectors flows through the fuel pressure regulator (2) before returning to the fuel tank. Fuel pressure is controlled by the fuel pressure regulator. Fuel pressure should be 482 + 138 - 103 kPa (70 + 20 - 15 psi) at Full Load rpm.
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Text Reference
FUEL SYSTEM
Engine Block Engine Oil Renewal Solenoid
Fuel Tank Primary Fuel Filter Fuel Heater
Fuel Pressure Regulator
Cylinder Head Fuel Transfer Pump
Fuel Priming Pump Secondary Fuel Filters
Engine Ecm
Cylinder Head
88
Fuel is pulled from the tank through a fuel heater, if equipped, and sent through the primary fuel filter by the fuel transfer pump. Fuel flows from the transfer pump through the Engine ECM to the secondary fuel filters. Fuel flows from the fuel filter base through the fuel injectors in the cylinder heads. Return fuel from the injectors flows through the fuel pressure regulator before returning through the fuel heater to the tank. If equipped with the engine oil renewal system, engine oil flows from the engine block through an oil filter to the engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel. The engine oil mixes with the fuel in the tank and flows with the fuel to the injectors to be burned.
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Text Reference
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2
89
Air Induction and Exhaust System
The engine receives clean air through the air filters located on the front of the truck (789C) or on either side of the engine (785C). Any restriction caused by plugged filters can be checked at the filter restriction indicators (1). If the yellow piston is in the red zone, the filters must be cleaned or replaced. Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. The dust valve is OPEN when the engine is OFF and closes when the engine is running. The dust valve must be flexible and close when the engine is running or the precleaner will not function properly and the air filters will have a shortened life. Replace the rubber dust valve if it becomes hard and not flexible. The VIMS will also provide the operator with an air filter restriction warning when the filter restriction is approximately 6.2 kPa (25 in. of water). Black exhaust smoke is also an indication of air filter restriction. Two filter elements are installed in the filter housings. The large element is the primary element and the small element is the secondary element.
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Text Reference
1
2
90
The turbocharger inlet pressure sensor (1) is located in a tube between the air filters and the turbochargers. The Engine ECM uses the turbocharger inlet pressure sensor in combination with the atmospheric pressure sensor to determine air filter restriction. The ECM provides the input signal to the VIMS, which informs the operator of the air filter restriction. If air filter restriction exceeds 6.25 kPa (25 in. of water), an air filter restriction event will be logged, and the ECM will derate the fuel delivery (maximum derating of 20%) to prevent excessive exhaust temperatures. A factory password is required to clear this event. If the Engine ECM detects a turbocharger inlet pressure sensor fault, the ECM will derate the engine to the maximum rate of 20%. If the Engine ECM detects a turbocharger inlet and atmospheric pressure sensor fault at the same time, the ECM will derate the engine to the maximum rate of 40%. The Engine ECM will automatically inject ether from the ether cylinders (2) during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch in the cab on the center console (see Visual No. 48). The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1900 rpm.
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Text Reference
91
Shown is the 3516B engine used in the 789C truck. The 3516B engine is equipped with four turbochargers (arrows). The 785C truck has a 3512B engine with two turbochargers. The turbochargers are driven by the exhaust gas from the cylinders which enters the turbine side of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, and the mufflers. The clean air from the filters enters the compressor side of the turbochargers. The compressed air from the turbochargers flows to the aftercoolers. After the air is cooled by the aftercoolers, the air flows to the cylinders and combines with the fuel for combustion.
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Text Reference
92
An exhaust temperature sensor (arrow) is located in ea ch exhaust manifold before the turbochargers. The two exhaust temperature sensors provide input signals to the Engine ECM. The ECM provides the input signal to the VIMS, which informs the operator of the exhaust temperature. Some causes of high exhaust temperature may be faulty injectors, plugged air filters, or a restriction in the turbochargers or the muffler. If the exhaust temperature is above 750°C (1382°F), the Engine ECM will derate the fuel delivery to prevent excessive exhaust temperatures. The ECM will derate the engine by 2% for each 30 second interval that the exhaust temperature is above 750°C (1382°F) (maximum derate of 20%). The ECM will also log an event that requires a factory password to clear.
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Text Reference
From Air Filters
Muffler
3512B AIR INDUCTION AND EXHAUST SYSTEM
Aftercooler
From Air Filters
93
This schematic shows the flow through the air induc tion and exhaust system. The turbochargers are driven by the exhaust gas from the cylinders which enters the turbine side of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, and the mufflers. The clean air from the filters enters the compressor side of the turbochargers. The compressed air from the turbochargers flows to the aftercoolers. After the air is cooled by the aftercoolers, the air flows to the cylinders and combines with the fuel for combustion.
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Text Reference
POWER TRAIN 785C
94
POWER TRAIN
Power flows from the engine to the rear wheels through the power train. The components of the power train are: - Torque converter - Transfer gears - Transmission - Differential - Final drives INSTRUCTOR NOTE: In this section of the presentation, component locations and a brief description of the component functions are provided.
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Text Reference
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95
Torque Converter
The first component in the power train is the torque converter. The torque converter provides a fluid coupling that permits the engine to continue running with the truck stopped. In converter drive, the torque converter multiplies engine torque to the transmission. At higher ground speeds, a lockup clutch engages to provide direct drive. The NEUTRAL and REVERSE ranges are converter drive only. FIRST SPEED is converter drive at low ground speed and direct drive at high ground speed. SECOND through SIXTH SPEEDS are direct drive only. The torque converter goes to converter drive between each shift (during clutch engagement) to provide smooth shifts. Mounted on the torque converter are the inlet relief valve (1), the outlet relief valve (2), and the torque converter lockup clutch control valve (3). A torque converter outlet temperature sensor (4) provides a n input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends the signal to VIMS, which informs the operator of the torque converter outlet temperature. A Converter Output Speed (COS) sensor (5) send s an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM uses the information to calculate shift times for the torque converter lockup clutch and the transmission clutches. The shift time information is sent to VIMS for shift time analysis.
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Lockup Piston
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Turbine
Text Reference
TORQUE CONVERTER
Impeller Stator
CONVERTER DRIVE
Torque Converter Inlet Oil
Freewheel Assembly
Torque Converter Lockup Oil Passage
96
This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch (yellow piston and blue discs) is not engaged. During operation, the rotating housing and impeller (red) can rotate faster than the turbine (blue). The stator (green) remains stationary and multiplies the torque transfer between the impeller and the turbine. The output shaft rotates slower than the engine crankshaft, but with increased torque.
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Lockup Piston
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Turbine
Text Reference
TORQUE CONVERTER
Impeller
Stator
DIRECT DRIVE
Torque Converter Inlet Oil
Freewheel Assembly
Torque Converter Lockup Oil Passage
97
In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure and locks the turbine to the impeller. The housing, impeller, turbine, and output shaft then rotate as a unit at engine rpm. The stator, which is mounted on a freewheel assembly, is driven by the force of the o il in the housing and will freewheel at approximately the same rpm.
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Text Reference
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4
5
2
1
98
Torque Converter Hydraulic System
The three (785C) or four (789C) section torque converter pump is located at the bottom rear of the torque converter. The four sections (from the front to the rear) are: - Torque converter scavenge (1) - Torque converter charging (2) - Parking brake release (3) - Rear brake oil cooling (4) (789C only) Excess oil that accumulates in the bottom of the torque converter is scavenged by the first section of the pump through a screen behind the access cover (5) and returned to the hydraulic tank.
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Text Reference
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2
99
Oil flows from the torque converter charging section of the pump to the torque converter charging filter (1). An oil filter bypass switch (2) is located on the torque converter charging filter. The oil filter bypass switch provides an input signal to the VIMS, which informs the operator if the filter is restricted.
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Text Reference
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2
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100
Oil flows from the torque converter charging filter to the torque converter inlet relief valve (1). The inlet relief valve limits the maximum pressure of the supply oil to the torque converter. The torque converter inlet relief pressure can be measured at this valve by removing a plug and installing a pressure tap. Inlet relief pressure should not exceed 930 ± 35 kPa (135 ± 5 psi) at high idle when the oil is cold. Normally, the inlet relief pressure will be slightly higher than the outlet relief valve pressure. Oil flows through the inlet relief valve and enters the torque converter. Some of the oil will leak through the torque converter to the bottom of the housing to be scavenged. Most of the oil in the torque converter is used to provide a fluid coupling and flows through the torque converter outlet relief valve (2). The outlet relief valve maintains the minimum pressure inside the torque converter. The main function of the outlet relief valve is to keep the torque converter full of oil to prevent cavitation. The outlet relief pressure can be measured at the tap (3) on the outlet relief valve. The outlet relief pressure should be: 785C: 345 to 585 kPa (50 to 85 psi) at 1640 ± 65 rpm (TC Stall) 789C: 345 to 585 kPa (50 to 85 psi) at 1715 ± 65 rpm (TC Stall)
A torque converter outlet temperature sensor (4) provides a n input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to VIMS, which informs the operator of the torque converter outlet temperature.
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Text Reference
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3
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101
Most of the oil from the torque converter outlet relief valve flows through the torque co nverter outlet screen (1) located outside the left frame. A torque converter outlet screen bypass switch (2) provides an input signal to the VIMS, which informs the operator if the torque converter outlet screen is restricted. Oil flows from the torque converter outlet screen to the front brake oil cooler located behind the engine. Oil flows from the parking brake release section o f the torque converter pump to the parking brake release filter (3). A parking brake release filter bypass switch (4) is located on the parking brake release filter. The bypass switch provides an input signal to the Brake ECM. The Brake ECM sends a signal to VIMS, which informs the operator if the parking brake release filter is restricted.
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Text Reference
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1
102
The oil from the torque converter outlet screen flows through a diverter valve (1) before flowing through the front brake oil cooler (2). When the retarder or service brakes are ENGAGED, the oil is diverted through the cooler to the brakes. When the brakes are RELEASED, the oil bypasses the cooler and flows directly to the brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).
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Text Reference
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2
103
Oil from the parking brake release filter flows to the parking brake release valve (1). The parking brake release section of the torque converter pump provides supply oil for several purposes: - Release the parking brakes - Engage the torque converter lockup clutch - Hoist valve pilot oil - Front (789C) or rear (785C) brake oil cooling The parking brake relief valve (2) controls the pressure for parking brake release, torque converter lockup and hoist valve pilot oil. The parking brake release pressure is 4700 ± 200 kPa (680 ± 30 psi). Most of the oil from the parking brake release valve flows to the front brake oil cooler on the 789C truck and to the rear brake oil coolers on the 785C truck.
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Text Reference
2 1
3
4
104
The parking brake release pump supplies oil to the torque converter lockup clutch valve through the inlet port (1). When the lockup clutch solenoid (located on the transmission housing) is energized by the Transmission/Chassis ECM, transmission pump supply oil (signal oil) enters the lockup valve through the center hose (2). The signal oil pressure is approximately 1725 kPa (250 psi). The signal oil causes the lockup valve to start the modulation process for torque converter lockup. The lockup clutch valve then supplies oil to ENGAGE the lockup clutch in the torque converter. Torque converter lockup clutch pressure can be measured at the tap (3). Torque converter lockup clutch pressure should be 2135 ± 70 kPa (310 ± 10 psi) at 1300 rpm or higher. Do not check the torque converter lockup clutch pressure below 1300 rpm. The Converter Output Speed (COS) sensor (4) sends an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM memory also contains the engine rpm and the Transmission Output Speed (TOS) for each gear of the transmission. The Transmission/Chassis ECM provides all of these input signals to the VIMS. Using the information from the Transmission/Chassis ECM, the VIMS calculates if any slippage exists in the torque converter lockup clutch or any transmission clutches and stores this information in the VIMS main module. This information can be downloaded from the VIMS with a laptop computer.
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Text Reference
TORQUE CONVERTER LOCKUP CLUTCH CONTROL DIRECT DRIVE Lockup Clutch Pilot Pressure (RV) Signal Oil Lockup Modulation Valve
Selector Piston
Lockup Solenoid
To Lockup Clutch (LU)
To Transmission Lube
From Transmission Charge Pump
Lockup Reducing Valve
To Station "D" Shuttle Valve Relay Valve
From Parking Brake Release Pump (PMP)
105
Shown is a sectional view of the torque converter lockup clutch valve in DIRECT DRIVE. Supply oil from the parking brake release pump is used to provide lockup clutch oil. First, supply pressure is reduced to provide pilot pressure to the relay valve. Supply oil to the pressure reduction valve flows through cross-drilled orifices in the spool, past a check valve, and enters the slug chamber. The check valve dampens spool movement and reduces the possibility of valve chatter and pressure fluctuation. Oil pressure moves the slug in the right end of the spool to the right and the spool moves to the left against the spring force. The slug reduces the effective area on which the oil pressure can push. Because of the reduced effective area, a smaller, more sensitive spring can be used. Pilot pressure will be equal to the force of the spring on the left end of the spool. The spring force can be adjusted with shims. Pilot pressure is 1725 ± 70 kPa (250 ± 10 psi). When the lockup solenoid is energized, transmission pump supply (signal) pressure is directed to the relay valve. Before moving the selector piston, the pilot oil moves a shuttle valve to the right, which closes the lower left drain passage and opens the check valve. Oil then flows to the selector piston. Moving the selector piston blocks the upper drain passage, and the load piston springs are compressed.
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Text Reference
When the solenoid is energized, supply oil from the parking brake release pump is reduced to provide the lockup clutch pressure. Lockup clutch pressure depends mainly on the force of the load piston valve springs. When the solenoid is energized, pilot oil moves the selector piston down against a stop. When the load piston that compresses the springs is at the top against the selector piston, lockup clutch pressure is at its lowest controlled value. This value is called "primary pressure." As the load piston moves down, lockup clutch pressure increases gradually until the load piston stops. Maximum lockup clutch pressure is then reached. The gradual increase in pressure, which depends on how fast the load piston moves, is called "modulation." The speed of the load piston movement depends on how fast the oil can flow to the area above the load piston. The load piston orifice meters the flow of oil to the load piston chamber and determines the modulation time. Primary pressure is adjusted with shims in the load piston. Final lockup clutch pressure is not adjustable. If the primary pressure is correct and final lockup clutch pressure is incorrect, the load piston should be checked to make sure that it moves freely in the selector piston. If the load piston moves freely, the load piston springs should be replaced.
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Text Reference
TORQUE CONVERTER HYDRAULIC SYSTEM
Front Brakes
Rear Brakes
To Hoist Solenoid Manifold
Torque Converter Charging Filter Outlet Relief Valve
Front Brake Oil Cooler
Converter Lockup Valve
Inlet Relief Valve Diverter Valve
Parking Brake Release Valve
Rear Brake Oil Coolers Converter Outlet Screen
Parking Brake Filter
Converter Scavenge Screen
106
This schematic shows the flow of oil from the torque converter pump through the torque converter hydraulic system on the 789C truck. The scavenge pump section pulls oil through a screen from the torque converter housing and sends the oil to the hydraulic tank. The charging pump section sends oil through the torque converter charging filter to the torque converter inlet relief valve. Oil flows from the inlet relief valve through the torque converter to the outlet relief valve. Oil flows from the outlet relief valve through the converter outlet filter and the front brake oil cooler to the front brakes. The parking brake release pump section sends oil through the parking brake release filter to the parking brake release valve and the torque converter lockup clutch valve. Most of the oil flows through the parking brake release valve and the front brake oil cooler to the front brakes. The brake cooling pump section of the torque converter pump (789C only) sends oil through the two oil coolers located on the right side of the engine to the rear brakes.
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Text Reference
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3
1
107
Transmission and Transfer Gears
Power flows from the torque converter through a drive shaft to the transfer gears (1). The transfer gears are splined to the transmission input shaft. The transmission (2) is located between the transfer gears and the differential (3). The transmission is electronically controlled and hydraulically operated as in all other ICM (Individual Clutch Modulation) transmissions in Ca terpillar rigid frame trucks. The differential is located in the rear axle housing behind the transmission. Power from the transmission flows through the differential and is divided equally to the final drives in the rear wheels. The final drives are double reduction planetaries.
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Text Reference
1 2 3
108
Oil flows from the transmission oil cooler to the transfer gears through a hose (1). Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components. The transmission lube pressure relief valve is in the transmission case near the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission lube circuit. Transmission lube oil pressure can be measured at the tap (2). At HIGH IDLE, the transmission lube pressure should be 140 to 205 kPa (20 to 30 psi). At LOW IDLE, the transmission lube pressure should be a minimum of 4 kPa (.6 psi). The Transmission Output Speed (TOS) sensor (3) is located on the front of the transfer gears. A small shaft runs from the speed sensor location through the entire length of the transmission and engages the transmission output shaft. The transmission speed sensor signal serves many purposes. Some of the purposes are: - Transmission automatic shifting - Speedometer operation - Traction Control System (TCS) top speed limit - Truck Production Management System (TPMS) distance calculations - Machine speed input to VIMS to determine some warning categories
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Text Reference
POWER SHIFT PLANETARY TRANSMISSION
1
2
3 4 5
6
109
The transmission is a power shift planetary design which con tains six hydraulically engaged clutches. The transmission provides six FORWARD speeds and one REVERSE speed.
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1
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110
Transmission Hydraulic System
The transmission pump pulls oil through a suction screen from the transmission tank (see Visuals No. 12 and 159) located on the right side of the truck. The three-section transmission pump is mounted on the rear of the pump drive, which is located inside the right frame near the torque converter. The three sections are: - Transmission scavenge (1) - Transmission lube (2) - Transmission charging (3) The transmission scavenge section pulls oil through the magnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is sent to the transmission tank.
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Text Reference
111
Shown is the location of the transmission magnetic scavenge screens (arrow). These screens should always be checked for debris if a problem with the transmission is suspected. Oil is scavenged from the transmission by the first section of the transmission pump (see Visual No. 110).
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Text Reference
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1
3
112
Oil flows from the charging section of the transmission pump to the transmission charging filter (1) located on the frame behind the right front tire. Oil flows from the transmission charging filter to the transmission control valve located on top of the transmission. A transmission oil temperature sensor (2) is located in the tube between the transmission charging filter and the transmission control valve. The temperature sensor provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to VIMS, which informs the operator of the transmission oil temperature. Oil flows from the lube section of the transmission pump to the transmission lube filter (3). Oil flows from the transmission lube filter through the transmission oil cooler to the transfer gears. Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components. An oil filter bypass switch is located on each filter. The oil filter bypass switches provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the operator if the filters are restricted. Transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4).
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Text Reference
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1
113
Oil flows from the transmission lube filter and the transmission control valve through the transmission oil cooler bypass valve (1) to the transmission oil cooler (2). The bypass valve for the transmission oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is restricted. Oil flows from the transmission oil cooler to the transfer gears and the transmission to cool and lubricate the internal components.
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Text Reference
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5
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114
The transmission charging pump supplies oil to the transmission hydraulic control valve and the shift solenoids through the inlet port (1). Excess transmission charging oil either drops to the bottom of the housing to be scavenged or flows to the transmission oil cooler through the outlet hose (2). The torque converter lockup clutch solenoid (3) is energized by the Transmission/Chassis ECM when DIRECT DRIVE (lockup clutch ENGAGED) is required. Transmission charge pump supply (signal) oil flows through the small hose (4) to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch. The transmission charging pressure relief valve is part of the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission charging circuit. Transmission charging pressure can be measured at the tap (5).
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Text Reference
1
4
2
3
115
Shown is the Individual Clutch Modulation (ICM) transmission hydraulic control valve. Transmission clutch pressures are measured at the pressure taps (1). The transmission hydraulic control valve contains a priority valve. The priority valve controls the pressure that is directed to the selector pistons in each of the clutch stations. The transmission priority valve pressure is 1720 kPa (250 psi). The transmission lube pressure relief valve (2) limits the maximum pressure in the transmission lube circuit. The "D" Station (3) is used to control the dual stage relief valve setting for the clutch supply pressure. In DIRECT DRIVE, the pressure measured at the tap for station "D" will be approximately 1380 kPa (200 psi). This valve station is adjusted to obtain the correct transmission charge pressure in DIRECT DRIVE. At LOW IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be 2515 kPa (365 psi) minimum. At HIGH IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be 3175 kPa (460 psi) maximum. During torque converter lockup (DIRECT DRIVE), clutch supply pressure is reduced to extend the life of the transmission clutch seals. At 1300 rpm in DIRECT DRIVE, the clutch supply pressure should be 2020 + 240 - 100 kPa (293 + 35 - 15 psi). The corresponding transmission charge pressure is reduced to 2100 ± 100 kPa (305 ± 15 psi).
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Text Reference
To test the transmission clutch pressures in torque converter lockup (DIRECT DRIVE), disconnect the signal line (4) and install a plug in the hose and a cap on the fitting. An 8T5200 Signal Generator/Counter can be used to shift the transmission during the diagnostic tests. If a Signal Generator is not available, disconnect the upshift and downshift solenoids and rotate the rotary selector spool manually by inserting a 1/4 in. ratchet extension through the transmission case.
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Text Reference
TRANSMISSION ICM HYDRAULIC SYSTEM
Upshift Pressure Lockup Downshift Upshift Solenoid Solenoid Solenoid
On
Downshift Pressure
A
Rotary Actuator
3
E N1
To Torque Converter Relay Valve
Priority Neutralizer Reduction Valve Valve
Pilot Oil Pressure
B
Rotary Selector Spool
F
Pump Pressure Filters Charging Pump
Lube Pump
C
Scavenge Pump
Oil Cooler
G D
Cooler Bypass Valve
H
Lube Pressure
Relief Valve Transmission Tank Transmission Case
Selector Valve Group
Lockup Dual Stage Relief Valve
Pressure Control Group
Lubrication Relief Valve
116
Shown is a sectional view of the ICM transmission hydraulic control valve group. The rotary selector spool is in a position that engages two clutches. Pump supply oil from the lockup solenoid flows to the selector piston in station "D." Station "D" reduces the pump supply pressure, and the reduced pressure flows to the lower end of the relief valve. Providing oil pressure to the lower end of the relief valve reduces the clutch supply pressure.
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Text Reference
785C / 789C TRANSMISSION HYDRAULIC SYSTEM
Transmission Charging Filter
Transmission Lube Filter Transmission Oil Cooler
Signal To Lockup Valve Relay
Transmission Pump
Lube Port Magnetic Scavenge Screens
117
Shown is the transmission hydraulic system. The transmission pump pulls oil through a suction screen from the transmission tank. The three-section transmission pump is mounted on the rear of the pump drive, which is located inside the right frame near the torque converter. The three sections are: - Transmission scavenge - Transmission lube - Transmission charging The transmission scavenge section pulls oil through the ma gnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is sent to the transmission tank.
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Text Reference
Oil flows from the charging section of the transmission pump to the transmission charging filter. Oil flows from the transmission charging filter to the transmission control valve located on top of the transmission. Transmission charging oil flows from the transmission control valve and joins with the oil from the transmission lube section of the transmission pump. Oil flows from the lube section of the transmission pump to the transmission lube filter. Oil from the transmission lube filter and the transmission control valve flows through the transmission oil cooler. Oil flows from the transmission oil cooler to the transfer gears and the transmission to cool and lubricate the internal compone nts.
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Text Reference
3 1
4
2
118
Differential
Shown is the differential removed from the rear axle housing. The rear axle cooling and filter system starts with a rear axle pump (1) that is driven by the differential. Since the pump rotates only when the machine is moving, no oil flow is produced when the machine is stationary. Cooling oil flow increases with ground speed to provide cooling when it is most needed. The rear axle pump pulls oil from the bottom of the rear axle housing through a suction screen (2). Oil flows from the pump through a temperature and flow control valve located on top of the differential housing to a filter mounted on the rear of the axle housing. Oil then flows from the filter back to the valve located on top of the differential housing. Oil then flows from the valve to the rear wheel bearings and the differential bearings. Oil flows through tubes (3) to the differential bearings. The fiberglass shroud (4) reduces the temperature of the rear axle oil on long hauls by reducing the oil being splashed by the bevel gear.
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Text Reference
2 4
3 1
5
119
Oil flows from the pump through the large hose (1) to the rear axle temperature and flow control valve (2). A differential oil temperature sensor (3) and pressure sensor (4) are located on the temperature and flow control valve. The sensors provide input signals to the Brake ECM. The Brake ECM sends signals to the VIMS. The differential temperature sensor input signal is used to warn the operator of a high rear axle oil temperature condition or to turn on the attachment rear axle cooling fan (if equipped). The differential oil pressure sensor input signal is used to warn the operator of a HIGH or LOW rear axle oil pressure condition. A HIGH oil temperature warning is provided if the temperature is above 118°C (244°F). A LOW oil pressure warning is provided if the pressure is below35 kPa (5 psi) when the differential oil temperature is above 52°C (125°F) and the ground speed is higher than 24 km/h (15 mph). A HIGH oil pressure warning is provided if the pressure is above 690 kPa (100 psi) when the differential oil temperature is above 52°C (125°F).
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Text Reference
The temperature and pressure control valve (2) prevents high oil pressure when the rear axle oil is cold. When the oil temperature is below 43°C (110°F), (110°F), the valve is OPEN and allows oil to flow to the rear axle housing. When the oil temperature is above 43°C (110°F), the valve is CLOSED and all the oil flows through the filter to a flow control valve located in the temperature and flow control valve. The temperature and pressure control valve is also the system main relief valve. If the pressure exceeds 690 kPa (100 (100 psi), the temperature and pressure control valve will open to prevent high oil pressure to the rear axle oil filter. filter. The flow control valve distributes the oil flow to the rear wheel bearings and the differential bearings. Oil flows from the temperature and flow control valve to the differential oil filter mounted on the rear of the axle housing. Oil then flows from from the filter back to to the temperature and flow control valve. Some of the oil that flows from the temperature temperature and flow control valve flows through the small supply hose (5) to the differential bearings.
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Text Reference
1
3
2
120
The differential oil filter bypass switch (1) and the two rear axle oil level switches (2) (one behind differential filter) provide input signals signals to the Brake ECM. The Brake ECM sends signals to the VIMS. The differential oil filter bypass switch signal is used to warn the operator when the differential oil filter is restricted. The rear axle oil level switch input signals are used to warn the operator o perator when the rear axle oil level is LOW. When the truck is initially put into operation, a 1R0719 (40 micron) filter is installed. installed. This filter removes the rust inhibitor used during manufacturing. The 40 micron filter should should be changed after the first 50 hours of operation and replaced with a 4T3131 (13 micron) filter. filter. The 13 micron filter should be changed every 500 hours. A differential carrier carrier thrust pin is located behind the small cover (3). The thrust pin prevents movement of the differential carrier during high thrust load conditions.
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Text Reference
REAR AXLE OIL COOLING AND FILTER SYSTEM Oil Cooler
Oil Filter
Temperature and Flow Control Valve Temperature / Pressure Control Valve
Differential Oil Pump
Rear Axle
Suction Screen
121
Shown is a schematic of the the rear axle oil cooling and filter filter system. The differential oil pump pulls oil from the bottom of the rear axle housing through a suction screen. Oil flows from the pump through a temperature and flow control valve located on top of the differential housing. The temperature and pressure control valve, which is part of the temperature and flow control valve, prevents high oil pressure when the rear axle oil is cold. When the oil temperature is below 43°C (110°F), the valve is OPEN and allows oil to flow flow to the rear axle housing. When the oil temperature is above 43°C (110°F), the valve is CLOSED and all the oil flows through the differential oil filter and the oil cooler (if equipped) to a flow control valve, which is also part of the temperature and flow control valve. The temperature and pressure control valve is also the system system main relief valve. If the pressure exceeds 690 kPa (100 psi), the temperature and pressure control valve will open to prevent high oil pressure to the rear axle oil filter filter.. The flow control valve distributes the oil flow to the rear wheel bearings and the differential bearings. At high ground speeds, excess oil flow is diverted to the axle housing to prevent overfilling the wheel bearing and final drive compartments.
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First Reduction Ring Gear
Second Reduction Ring Gear
Text Reference
Second Reduction Carrier Second Reduction Planetary Gear
Second Reduction Sun Gear
FINAL DRIVE
First Reduction Sun Gear
First Reduction Carrier
First Reduction Planetary Gear
122
Final Drives
Shown is a sectional view of the double reduction planetary gear final drive. drive. Power flows from the differential through axles to the sun gear of the first reduction planetary set. The ring gears of the first reduction planetary set and the second reduction planetary set cannot rotate. Since the ring gears cannot rotate, the first reduction sun gear causes rotation of the first reduction planetary gears and the first reduction carrier. carrier. The first reduction carrier carrier is splined to the the second reduction sun gear. gear. The second reduction sun gear causes rotation of the second reduction planetary gears and the second reduction carrier. Since the second reduction carrier c arrier is connected to the wheel assembly a ssembly,, the wheel assembly also rotates. The wheel assembly rotates much slower than the axle shaft but with increased torque.
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Text Reference
123
Transmission/Chassis Electronic Control System
The Transmission/Chassis Electronic Control Module (ECM) (arrow) is located in the compartment at the rear of the the cab. The transmission control used in the "B" Series trucks trucks is referred to as the second generation gen eration Electronic Programmable Transmission Control (EPTC II). The transmission control used in the "C" Series trucks performs the transmission control functions, plus some other machine functions functions (hoist control). Because of the added functionality of the control, it is now referred to as the "Transmission/Chassis ECM." The Transmission/Chassis ECM does not have a diagnostic window as in the EPTC II. Diagnostic and programming functions must be performed with an Electronic Control Analyzer Programmer (ECAP) or a laptop computer with the Electronic Technician (ET) software installed. ET is the tool of choice because the Transmission/Chassis Transmission/Chassis ECM can be reprogrammed reprogrammed with a "flash" file using the WinFlash WinFlash application of ET. ET. The ECAP cannot upload "flash" files. The Transmission/Chassis ECM appears identical to the Engine ECM with two 40-pin connectors, but the Transmission/Chassis Transmission/Chassis ECM does not have fittings for cooling fluid. Also, the Transmission/Chassis ECM has no access plate for a personality module.
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Text Reference
"C" SERIES TRUCK TRANSMISSION / CHASSIS ELECTRONIC CONTROL SYSTEM OUTPUT COMPONENTS
INPUT COMPONENTS Transmission Gear Switch Converter Output Speed Sensor Service / Retarder Brake Pressure Switch Body Position Sensor
Shift Lever Position Switch
CAT Data Link Electronic Service Tool Engine ECM
Transmission Output Speed Sensor
Brake ECM VIMS
Engine Output Speed Sensor
Upshift Solenoid Parking/secondary Brake Pressure Switch
Downshift Solenoid
Key Start Switch
Lockup Solenoid
Low Steering Pressure Switch Hoist Lever Position Sensor
Starter Solenoid
Hoist Screen Switch
Auto Lube Solenoid
Transmission Oil Temp Sensor Transmission Charge Filter Switch Transmission Lube Filter Switch
Back-up Alarm Relay
Body Up Lamp Hoist Lower Solenoid
Torque Converter Oil Temp Sensor
Hoist Raise Solenoid
124
The purpose of the Transmission/Chassis ECM is to determine the desired transmission gear and energize solenoids to shift the transmission up or down as required ba sed on information from both the operator and machine. The Transmission/Chassis ECM receives information (electrical signals) from various input components such as the shift lever switch, Transmission Output Speed (TOS) sensor, transmission gear switch, body position sensor, and the hoist lever sensor. Based on the input information, the Transmission/Chassis ECM determines whether the transmission should upshift, downshift, engage the lockup clutch, or limit the transmission gear. These actions are accomplished by sending signals to various output components. Output components include the upshift, downshift and lockup solenoids, the back-up alarm, and others. The Transmission/Chassis ECM also provides the service technician with enhanced diagnostic capabilities through the use of onboard memory, which stores diagnostic codes for retrieval at the time of service.
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Text Reference
The Engine Electronic Control, the Brake Electronic Control System (ARC and TCS), the Vital Information Management System (VIMS) and the Transmission/Chassis Electronic Control System all communicate through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the Transmission/Chassis ECM signals the Engine ECM to reduce or increase engine fuel during a shift to lower stress to the power train. The Transmission/Chassis ECM is also used to control the hoist, the automatic lubrication (grease), the neutral-start and the back-up alarm systems on the "C" Series trucks. Many of the sensors and switches that provided input signals to the VIMS interface modules on the "B" Series trucks have been moved to provide input signals to the Transmission/Chassis ECM and the Brake ECM. Sensors and switches that were in the VIMS and now provide input signals to the Transmission/Chassis ECM are: - Low steering pressure
- Hoist screen bypass
- Transmission oil temperature
- Transmission charge filter bypass
- Transmission lube filter bypass
- Torque converter oil temperature
The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used to perform several diagnostic and programming functions. Some of the diagnostic and programming functions that the service tools can pe rform are: - Display real time status of input and output parameters - Display the internal clock hour reading - Display the number of occurrences and the hour reading of the first and last occurrence for each logged diagnostic code and event - Display the definition for each logged diagnostic code and event - Display load counters - Display the lockup clutch engagement counter - Display the transmission gear shift counter - Program the top gear limit and the body up gear limit - Upload new Flash files
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Text Reference
3 2
1
125
The shift lever (also referred to as the "Can e" or "Gear Selector") switch (1) is located inside the cab in the shift console and provides input signals to the Transmission/Chassis ECM. The shift lever switch controls the desired top gear selected by the operator. The shift lever switch inputs consist of six wires. Five of the six wires provide codes to the Transmission/Chassis ECM. Each code is unique for each position of the shift lever switch. Each shift lever switch position results in two of the five wires sending a ground signal to the Transmission/Chassis ECM. The other three wires remain open (ungrounded). The pair of grounded wires is unique for each shift lever position. The sixth wire is the "Ground Verify" wire, which is normally grounded. The Ground Verify wire is used to verify that the shift lever switch is con nected to the Transmission/Chassis ECM. The Ground Verify wire allows the Transmission/Chassis ECM to distinguish between loss of the shift lever switch signals and a condition in which the shift lever switch is between detent positions. To view the shift lever switch positions or diagnose problems with the switch, use the VIMS message center module or the status screen of the ET service tool and observe the "Gear Lever" status. As the shift lever is moved through the detent positions, the Gear Lever status should display the corresponding lever position shown on the shift console. The position of the shift lever can be changed to obtain better alignment with the gear position numbers on the shift console by loosening the three nuts (2) and rotating the lever. The position of the shift lever switch is also adjustable with the two screws (3).
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Text Reference
4
2
3
1
126
The transmission gear switch (1) provides input signals to the Transmission/Chassis ECM. The transmission gear switch inputs (also referred to as the "actual gear inputs") consist of six wires. Five of the six wires provide codes to the Transmission/Chassis ECM. Each code is unique for each position of the transmission gear switch. Each transmission gear switch position results in two of the five wires sending a ground signal to the Transmission/Chassis ECM. The other three wires remain open (ungrounded). The pair of grounded wires is unique for each gear position. The sixth wire is the "Ground Verify" wire, which is normally grounded. The Ground Verify wire is used to verify that the transmission gear switch is connected to the Transmission/Chassis ECM. The Ground Verify wire allows the Transmission/Chassis ECM to distinguish between loss of the transmission gear switch signals and a condition in which the transmission gear switch is between gear detent positions. Earlier transmission gear switches use a wiper contact assembly that does not require a power supply to Pin 4 of the switch. Current transmission gear switches are Hall-Effect type switches. A power supply is required to power the switch. A small magnet passes over the Hall cells, which then provide a non-contact position switching capability. The Hall-Effect type switch uses the same 24-Volt power supply used to power the Transmission/Chassis ECM. The solenoid outputs provide +Battery voltage to the upshift solenoid (2), the downshift solenoid (3) or the lockup solenoid (4) based on the input information from the operator and the machine. The solenoids are energized until the transmission actual gear switch signals the Transmission/Chassis ECM that a new gear position has been reached.
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Text Reference
127
The Transmission Output Speed (TOS) sensor (arrow) is located on the transfer gear housing on the input side of the transmission. Although the sensor is physically located near the input end of the transmission, the sensor is measuring the speed of the transmission output shaft. The sensor is a Hall-Effect type sensor. Therefore, a power supply is required to power the sensor. The sensor receives 10 Volts from the Transmission/Chassis ECM. The sensor output is a square wave signal of approximately 10 Volts amplitude. The frequency in Hz of the square wave is exactly equal to twice the output shaft rpm. The signal from this sensor is used for automatic shifting of the transmission. The signal is also used to drive the speedometer and as an input to other electronic controls. An 8T5200 Signal Generator/Counter can be used to shift the transmission during diagnostic tests. Disconnect the harness from the lockup solenoid and the speed sensor and attach the Signal Generator to the speed sensor harness. Depress the ON and HI frequency buttons. Start the engine and move the shift lever to the highest gear position. Rotate the frequency dial to increase the ground speed and the transmission will shift. A 196-1900 adapter is required to increase the frequency potential from the signal generator when connecting to the ECM's used on these trucks. When using the signal generator, the lockup clutch will not engage above SECOND GEAR because the Engine Output Speed (EOS) and the Converter Output Speed (COS) verification speeds will not be correct for the corresponding ground speed signal. NOTE:
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2
Text Reference
4
5 3
1
128
The service/retarder brake switch (1) is located in the compartment behind the cab. The switch is normally closed and opens when service/retarder brake air pressure is applied. The switch has three functions for the Transmission/Chassis ECM: - Signals the Transmission/Chassis ECM to use elevated shift points, which provides increased engine speed during downhill retarding for increased oil flow to the brake cooling circuit. - Cancels Control Throttle Shifting (CTS). - Signals the Transmission/Chassis ECM to override the anti-hunt timer. Rapid upshifting and downshifting is always allowed. The anti-hunt timer prevents a rapid upshift-downshift sequence or a rapid downshift-upshift sequence (transmission hunting). The timer is active during normal operation. It is overridden when either the service/retarder or parking/secondary brakes are engaged. A diagnostic code is stored if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within two hours of operation time. The Traction Control System (TCS) also uses the service/retarder brake switch as an input through the CAT Data Link (see Visual No. 199).
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Text Reference
The parking/secondary brake switch (2) is in the parking/secondary brake air pressure line. The normally open switch is closed during the application of air pressure. The purpose of the switch is to signal the Transmission/Chassis ECM when the parking/secondary brakes are ENGAGED. Since the parking/secondary brakes are spring engaged and pressure released, the parking/secondary brake switch is closed when the brakes are RELEASED and opens when the brakes are ENGAGED. This signal is used to override the anti-hunt timer for rapid downshifting and is used to sense when the machine is parked. A diagnostic code is stored if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within one hour of operation time. Many relays (3) are located behind the cab. Some of these relays receive output signals from the Transmission/Chassis ECM, and the relays turn on the desired function. The back-up alarm relay is one of the Transmission/Chassis ECM output components located behind the cab. When the operator moves the shift lever to REVERSE, the Transmission/Chassis ECM provides a signal to the back-up alarm relay, which turns ON the back-up alarm. The system air pressure sensor (4) and the brake light switch (5) are also located in the compartment behind the cab. The low air pressure sensor provides an input signal to the Brake ECM. The Brake ECM sends a signal to the VIMS, which informs the operator of the system air pressure condition.
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Text Reference
2
1
129
The body position sensor (1) is located on the frame near the left body pivot pin. A rod assembly (2) is connected between the sensor and the body. When the body is raised, the rod rotates the sensor, which changes the Pulse Width Modulated (PWM) signal that is sent to the Transmission/Chassis ECM. The adjustment of the rod between the sensor and the body is very important. The length of the rod must be within 10 mm (.39 in.) of the following dimensions (center to center of the rod ends): 350 ± 3 mm (13.78 ± .12 in.) After the rod has been adjusted, a calibration should be performed. The body position sensor is calibrated by the Transmission/Chassis ECM when the following conditions occur: - Engine is running - Hoist output is in FLOAT or LOWER - No ground speed is present for one minute - Body position sensor duty cycle output is stable for 23 seconds (body is down) - Body position is different than previous calibration - Duty cycle output from the sensor is between 3% and 30% Use the VIMS display to view the body position. When the body is down, the VIMS should display zero degrees. If the position is greater than zero degrees, the sensor rod may have to be adjusted.
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Text Reference
The body position signal is used for several purposes. -
Body up gear limiting Hoist snubbing Signals a new load count (after 10 seconds in RAISE position) Lights the body up dash lamp Allows the VIMS to provide body up warnings
The body position sensor signal is used to limit the top gear into which the transmission will shift when the body is UP. The body up gear limit value is programmable from FIRST to THIRD gear using the ECAP or ET service tool. The Transmission/Chassis ECM comes from the factory with this value set to FIRST gear. When driving away from a dump site, the transmission will not shift past the programmed gear until the body is down. If the transmission is already above the limit gear when the body goes up, no limiting action will take place. The body position sensor signal is also used to control the SNUB position of the hoist control valve. When the body is being lowered, the Transmission/Chassis ECM signals the hoist LOWER solenoid to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame. The body position sensor signal is used to provide warnings to the operator when the truck is moving with the body UP. The faster the ground speed, the more serious the warning. The body position sensor receives + Battery Voltage (24 Volts) from the Chassis ECM. To check the supply voltage to the sensor, connect a multimeter between Pins A and B of the connector. Set the meter to read "DC Volts." The body position sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the body position. To check the output signal of the body position sensor, disconnect the rod and connect a multimeter between Pins B and C of the connector. Set the meter to read "Duty Cycle." The duty cycle output of the body position sensor should change smoothly between 3% and 98% when rotated. The duty cycle should be low when the body is DOWN and high when the body is UP.
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Text Reference
STEERING 789C
130
STEERING SYSTEM
This section of the presentation explains the operation of the steering system. As on other Caterpillar Off-highway Trucks, the steering system uses hydraulic force to change the direction of the front wheels. The system has no mechanical connection between the steering wheel and the steering cylinders. If the oil flow is interrupted while the truck is moving, the system incorporates a secondary steering system. Secondary steering is accomplished by accumulators which supply oil flow to maintain steering. The steering system on the "C" Series trucks is the same as the steering system on the "B" Series trucks. No changes were made to the steering system.
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Text Reference
789C STEERING SYSTEM
High Steering Pressure Switch
NO STEER / MAXIMUM FLOW Steering Directional Valve
Solenoid and Relief Valve Return Manifold
R
L
P
Case Drain Filter
T LS
Piston Pump
Accumulator Charging Valve
Low Steering Pressure Switch
Hand Metering Unit
131
When the engine is started, oil for the steering system is drawn from the steering hydraulic tank by the steering pump and sent through a one-way check valve to the solenoid and relief valve manifold. Oil from the solenoid and relief valve manifold flows to the steering directional valve, the accumulator charging valve and the accumulators. After the oil pressure increases to a predetermined pressure in both accumulators, the steering pump will destroke. When a steering demand occurs, the accumulators supply the necessary oil flow for steering, and pressure in the accumulators decreases. When the oil pressure in the accumulators decreases to a predetermined level, the steering pump will automatically upstroke to maintain the oil pressure required for steering in the accumulators. Oil from the accumulators flows through the steering directional valve to the Hand Metering Unit (HMU). If the steering wheel is not turned, the oil flows through the HMU and the main steering oil filter to the tank.
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Text Reference
Allowing oil to circulate through the HMU while the steering wheel is stationary provides a "thermal bleed" condition, which maintains a temperature differential of less than 28°C (50°F) between the HMU and the tank. This "thermal bleed" prevents thermal seizure of the HMU (sticking steering wheel). When the steering wheel is turned, the HMU directs oil back to the steering directional valve. The steering directional valve directs oil to the steering cylinders. Depending on which direction the steering wheel is turned, oil will flow to the head end of one steering cylinder and to the rod end of the other cylinder. The action of the oil on the pistons and rods in the steering cylinders causes the wheels to change direction. Displaced oil from the steering cylinders flows through the back pressure valve in the steering directional valve and returns through the main steering oil filter to the tank.
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Text Reference
785C STEERING SYSTEM HOLD
Case Drain Filter
Crossover Relief Valves
Piston Pump Pump Switch
Hand Metering Unit
Solenoid and Relief Valve Return Manifold
132
Oil from the steering pump flows through a one -way check valve to the solenoid and relief valve return manifold and is then sent to the accumulators and the Hand Metering Unit (HMU). The 785C truck does not use a steering directional valve. Oil from the HMU flows through a crossover relief valve group directly to the steering cylinders. In the HOLD position, oil flows through an orifice in the HMU to the tank. Allowing oil to flow through the HMU in the HOLD position provides a "thermal bleed" condition, which prevents thermal seizure of the HMU (sticking steering wheel). The crossover relief valves protect the steering cylinders and oil lines from pressure surges when the steering wheel is in the HOLD position by equalizing the oil pressure between the head ends and rod ends of the steering cylinders. During a turn, the HMU directs oil through the crossover relief valves to the steering cylinders. Displaced oil from the steering cylinders flows back through the HMU to the main steering oil filter.
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Text Reference
3 5
4
1
7
2
6
133
The steering tank is located on the right platform. Two sight gauges are on the side of the tank. When the engine is shut off and the oil is cold, the oil should be visible between the FULL and ADD OIL markings of the upper sight gauge (l). When the engine is running and the accumulators are fully charged, the oil level shou ld not be below the ENGINE RUNNING marking of the lower sight gauge (2). If the ENGINE RUNNING level is not correct, check the nitrogen charge in each accumulator. A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity. A combination vacuum breaker/pressure relief valve is used to limit the tank pressure. Before removing the fill cap, be sure that the engine was shut off with the ke y start switch and the oil has returned to the tank from the accumulators. Depress the pressure release button (3) on the breather to vent any remaining pressure from the tank. Supply oil for the steering system is provided by a piston-type pump. Case drain oil from the pump returns to the tank through the filter (4). The remaining steering system oil returns to the tank through the main steering filter (5). Both filters are equipped with bypass valves to protect the system if the filters are restricted or during cold oil start-up. If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at the connector to charge the steering accumulators. Steering capability is then available to tow the truck.
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Text Reference
The steering oil temperature sensor (7) provides an input signal to the VIMS, which informs the operator of the steering system oil temperature. If the steering oil temperature exceeds 108 °C (226 °F), the operator will receive a warning on the VIMS display (STRG OIL TEMP HI). INSTRUCTOR NOTE: For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).
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2
Text Reference
1
134
The piston-type steering pump (1) for the 785C truck is mounted to the pump drive. The pump drive is located on the inside of the right frame rail near the torque converter. The steering pump operates only when the engine is running and provides the necessary oil flow to the accumulators for steering system operation. The steering pump for the 785C truck contains a pressure compensator valve (2) that monitors and controls steering pump output.
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Text Reference
135
Shown is a sectional view of the piston-type steering pump for the 785C truck in the MAXIMUM FLOW condition. No oil pressure pressure is present in the control piston. In this condition, the swashplate is kept at maximum angle by the force of the spring in the pump housing. The pistons travel in and out of the barrel and maximum flow flow is provided through the outlet port. Since the pump is driven by a shaft shaft off the engine, it should be remembered that engine rpm also affects pump output.
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Text Reference
PUMP COMPENSATOR VALVE MAXIMUM PUMP FLOW
Drain Passages
MINIMUM PUMP FLOW
From Pump
Drain Passages
To Control Piston
From Pump To Control Piston
136
Shown is a sectional view of the pump compensator valve for the 785C truck. truck. The pump compensator valve senses pump supply pressure pressure through a passage in the valve body. When the outlet pressure is less than the force of the spring o n the end of the compensator spool, the oil is blocked from flowing to the pump control piston. As the accumulators fill, fill, the pressure of the oil through the pump outlet increases. increases. The pump supply pressure will increase until the pressure of the oil in the pump passage in the pump compensator valve is high enough to overcome the spring force on the compensator spool. spool. The spool then moves to the left left and opens the passage to the control control piston. This movement occurs when the outlet oil pressure is approximately 17580 ± 345 kPa (2550 ± 50 psi). The pressure setting can be adjusted by changing the shim thickness behind the compensator spool spring. Remove the plug and add shims to increase the pressure setting. Remove shims to lower the setting.
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Text Reference
7/05
785C STEERING PUMP MINIMUM FLOW Swashplate
Piston Supply Passage for Pump
Output Passage From Pump
Pressure Compensator Valve
Control Piston
137
The pressure of the oil from the compensator compe nsator valve passage moves the control piston, p iston, which rotates the swashplate toward toward the minimum angle. The pistons now have very little little movement in and out of the barrel as the retraction plate and slippers follow the minimum an gle of the swashplate. While the accumulators are filled, this small movement of the pistons maintains the pressure at the setting of the pressure pressure compensator valve. The compensator spool will remain remain open to provide pressure oil behind the control piston. Excess oil from the pump outlet goes into the pump case for cooling and lubrication. The oil then goes through a drain line to the case drain oil filter and steering hydraulic tank. As the steering wheel is turned and oil is taken from the accumulators, the pressure at the pump outlet will decrease. When accumulator pressure decreases, the pressure compensator valve will allow the swashplate to move toward maximum angle and increase pump output.
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Text Reference
3
4
1
2
138
The 789C is equipped with a load sensing, sensing, pressure compensated, piston-type pump (1). (1). The steering pump is mounted to the the pump drive. The pump drive is located on the inside inside of the right frame rail near the torque converter conve rter.. The steering pump operates only when the engine is running and provides the necessary flow of oil to the accumulators for steering system operation. The steering pump contains a load sensing sensing controller (2) that works with an accumulator charging valve to monitor and control steering pump output. The steering pump will produce flow at high pressure until the steering accumulators are charged with oil and the pressure increases to 18300 ± 350 kPa (2655 ± 50 psi) at LOW IDLE. This pressure is referred to as the CUT-OUT CUT-OUT pressure. When the CUT-OUT CUT-OUT pressure is reached, the accumulator charging valve reduces the load sensing signal pressure to the pump load sensing controller, and the pump destrokes to the LOW PRESSURE STANDBY STANDBY condition. During LOW PRESSURE STANDBY STANDBY,, the pressure should be between 2070 and 3600 3 600 kPa (300 and 525 psi). The pump operates at minimum swashplate angle to supply oil for lubrication and leakage. Because of the normal leakage in the steering system and Hand Metering Unit (HMU) "thermal bleed," the pressure in the accumulators will gradually decrease to 16470 ± 350 kPa (2390 ± 50 psi). This pressure is referred to as the CUT-IN CUT-IN pressure.
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Text Reference
When the pressure in the accumulators decreases dec reases to the CUT-IN CUT-IN pressure, the accumulator charging valve blocks the load sensing signal line to the load sensing controller from returning to the tank, and the pump upstrokes to maximum displacement (full flow). A pressure tap (3) is located on the pump pressure pressure switch manifold. If steering pump supply pressure is measured at this tap during LOW PRESSURE STANDBY STANDBY,, a gauge acceptable for testing maximum steering system pressure must be used to avoid damaging the gauge when the steering pump upstrokes to provide maximum oil flow. Two pressure switches monitor monitor the condition of the steering steering system on the 789C. One switch (4) monitors the output of the steering pump. This switch monitors pump supply pressure during LOW PRESSURE STANDBY STANDBY.. The VIMS refers to this switch as the "low steering pressure" switch. The other steering pressure switch is mounted on the bottom of one of the steering accumulators (see Visual Visual No. 153). This switch monitors the steering steering system accumulator pressure. The VIMS refers to this switch as the "high steering pressure" switch. Both steering pressure switches provide input signals to the Transmission/Chassis Transmission/Chassis ECM. The Transmission/Chassis Transmission/Chassis ECM sends signals to the VIMS, which informs the operator o f the condition of the steering system. system. A steering system warning warning is only displayed if the the ground speed is above 8 km/h (5 mph) or the actual gear gea r switch is not in NEUTRAL.
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Text Reference
1 4
2
6
3
5
139
On the 789C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold (2). The solenoid and relief valve manifold connects the steering pump to the accumulator charging valve (3), the accumulators and the steering directional valve (4). The solenoid and relief valve manifold also provides a path to drain for the steering oil. When checking the steering system CUT-OUT and CUT-IN pressures, a gauge can be connected at the pressure tap (5). Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (6).
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Text Reference
7/05
789C STEERING PUMP MAXIMUM FLOW From Accumulators
To Accumulators Accumulator Charging Valve
Pump Output Actuator Piston
Load Sensing Pressure Flow Compensator Load Sensing Controller Swashplate Piston
140
After the engine is started, pressure increases in the steering acc umulators. The pump load sensing controller is spring biased to vent the actuator piston pressure to drain. Venting pressure from the load sensing controller and the actuator piston positions the spring biased swashplate to maximum displacement (full flow). As pressure increases in the accumulators, pump supply p ressure is sensed in the accumulator charging valve and on both ends of the flow compensator. With pressure on both ends of the flow compensator, the swashplate is kept at maximum angle by the force of the spring in the pump housing and pump discharge pressure on the swashplate piston. The pistons travel in and out of the barrel and maximum flow is provided through the outlet port. Since the pump is driven by the engine, engine rpm also affects pump output. Because the signal lines are sensing pump supply pressure and not a "load" pressure, the steering system does not operate the same as other load sensing systems with a margin pressure. NOTE:
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Text Reference
789C STEERING PUMP LOW PRESSURE STANDBY From Accumulators
To Accumulators Accumulator Charging Valve
Pump Output
Actuator Piston
Load Sensing Pressure
Flow Compensator Load Sensing Controller Swashplate Piston
141
Pump supply pressure will increase until the accumulator pressure ac ting on the accumulator charging valve shifts the spool, and the load sensing signal pressure is vented to the tank. The accumulator charging valve spool shifts (cut-out) when the pump outlet oil pressure is approximately 18300 ± 350 kPa (2655 ± 50 psi). An orifice prevents supply pressure from filling the drained load sensing passage above the flow compensator. Pump oil (at low pressure standby pressure) flows past the lower end of the displaced flow compensator spool to the actuator piston. The actuator piston has a larger surface area than the swashplate piston. The oil pressure at the actuator piston overcomes the spring force of the swashplate piston and moves the swashplate to destroke the pump. The pump is then at a low flow, LOW PRESSURE STANDBY condition. Pump output pressure is equal to the setting of the flow compensator. The LOW PRESSURE STANDBY setting must be between 2070 and 3600 kPa (300 and 525 psi). In the NEUTRAL or NO STEER position, demand for oil from the accumulators is low. The pump operates at minimum swashplate angle to supply oil for lubrication and leakage. Because of the normal leakage in the steering system and HMU "thermal bleed," the pressure in the accumulators will gradually decrease to approximately 16470 ± 350 kPa (2390 ± 50 psi) (90% of the accumulator charging valve cut-out pressure).
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Text Reference
When the pressure in the accumulators decreases to 16470 ± 350 kPa (2390 ± 50 psi), the accumulator charging valve shifts (cut-in) and blocks the load sensing signal line pressure from the tank. Pump supply oil flows through the orifice and pressurizes the load sensing signal line. The load sensing signal shifts the flow compensator spool and drains the actuator piston oil to the tank. Venting pressure from the actuator piston positions the spring biased swashplate to maximum displacement (full flow). At LOW lDLE in the NEUTRAL or NO STEER position, the pump will cycle between the cut-out and cut-in conditions in 25 seconds or more. Connecting a pressure gauge to the pressure tap on the bottom of the steering directional valve will indicate these steering system pressures. If pump pressure cycles in less than 25 seconds, leakage is in the system and must be corrected. Typical sources of leakage can be the accumulator bleed down solenoid or the backup relief valve located on the return manifold.
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Text Reference
1
2
3
142
Shown is the accumulator charging valve (1). The accumulator charging valve is located on the frame rail near the front of the truck and below the engine oil pan. The pressure setting of the accumulator charging valve can be changed by adjusting the spring force that keeps the valve seated (closed). Change the setting by removing the protective cap (2) and turning the adjustment screw clockwise to increase or counterclockwise to decrease the pressure setting. Do not exceed 14 N•m (10 lb. ft.) torque on the adjustment screw when making the adjustments. One turn of the adjustment screw changes the pressure approximately 4000 kPa (580 psi). Operate the engine at LOW IDLE and check the pump (accumulator) pressure at the pressure tap (3). The pump will cycle between cut-out and cut-in every 25 seconds or more. The pressure gauge will indicate these steering system pressures. Turn the adjusting screw until the cut-out pressure is correct. If the accumulator charging pressure cannot be adjusted within specifications, an adjustment of the high pressure cutoff valve is required. The high pressure cutoff setting must be a minimum of 1720 kPa (250 psi) higher than the accumulator charging valve setting. NOTE: When testing or adjusting any steering system pressure settings, always allow the accumulator charge cycle to occur at least three times before testing the pressures. Failure to allow the charging cycle to occur three times will result in inaccurate readings.
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Text Reference
LOAD SENSING CONTROLLER From Accumulator Accumulator Charging Valve To Accumulator
Disconnect and Plug Line for High Pressure Cutoff Test
High Pressure Cutoff Adjustment Screw
Low Pressure Standby Adjustment Screw
To Tank To Actuator Piston From Pump Output Port
143
Pump pressure limiting (high pressure cutoff) is adjustable. To adjust the pump high pressure cutoff valve, turn the accumulator charging valve adjustment screw a ll the way in, or disconnect the load sensing (LS) line (pump to accumulator charging valve) at the pump. Plug the line to the accumulator charging valve and cap the fitting on the pump. Operate the engine at LOW IDLE, and check the pump (accumulator) pressure at the pressure tap below the steering directional valve. Turn the compensator (high pressure cutoff) adjusting screw while watching the pressure gauge. One turn is equal to approximately 2800 kPa (405 psi). Adjust the pressure to 20000 ± 350 kPa (2900 ± 50 psi). When the adjustment is complete, reconnect the LS line to the pump. The high pressure cutoff setting must be a minimum of 17 20 kPa (250 psi) higher than the accumulator charging valve setting. If the high pressure cutoff setting of the compensator valve (in the load sensing controller) is lower than the accumulator charging valve setting, the pump will stay at MINIMUM FLOW, and the steering system will take too long to recharge. The high pressure cutoff adjustment provides a back-up if the accumulator charging valve malfunctions.
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Text Reference
Pump LOW PRESSURE STANDBY is also adjustable. Connect a gauge to the low pressure standby pressure tap (see Visual No. 138). With the signal line connected, operate the engine at LOW IDLE and check the pump pressure. The pump will cycle to low pressure standby every 25 seconds or more. Low pressure standby must be between 2070 and 3600 kPa (300 and 525 psi). If adjustment is required, stop the engine. Turn the low pressure standby adjustment screw clockwise to increase the pressure and counterclockwise to decrease the pressure until the pressure is between 2070 and 3600 kPa (300 and 525 psi). Each 1/4 turn changes the pressure setting approximately 345 kPa (50 psi). NOTE: If the steering pump is adjusted on a hydraulic test stand, set the margin pressure to 2070 ± 100 kPa (300 ± 15 psi) with a flow of 115 ± 12 L/min (30 ± 3 gpm), 1838 rpm and 15000 kPa (2180 psi) discharge pressure. The low pressure standby reading measured on a truck is higher than the test stand margin pressure due to parasitic loads in the truck steering system.
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Text Reference
1
5
2
3
4
144
On the 789C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold. The solenoid and relief valve manifold connects the steering pump to the accumulator charging valve, the accumulators and the steering directional valve. The solenoid and relief valve manifold also provides a path to drain for the steering oil. The check valve (1) prevents accumulator oil from flowing back to the steering pump when the pump destrokes to LOW PRESSURE STANDBY. The accumulator bleed down solenoid (2) drains pressure oil from the accumulators when the truck is not in operation. The back-up relief valve (3) protects the system from pressure spikes if the pump cannot destroke fast enough or limits the maximum pressure if the steering pump high pressure cutoff valve does not open. Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (4). To operate the steering system on a disabled truck, an Auxiliary Power Unit (APU) can be connected to the secondary steering connector (5) on the solenoid and relief valve manifold and to a suction port on the hydraulic tank (see Visual No. 133). The APU will provide supply oil to charge the accumulators. Steering capability is then available to tow the truck.
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Text Reference
5
1
6
4 3
2
145
On the 785C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold. The solenoid and relief valve manifold connects the steering pump to the accumulators and the HMU. The solenoid and relief valve manifold also provides a path to drain for the steering oil. The check valve (1) prevents accumulator oil from flowing back to the steering pump The accumulator bleed down solenoid (not shown) drains pressure oil from the accumulators when the truck is not in operation. The back-up relief valve (2) limits the maximum pressure if the steering pump compensator valve fails. Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (3) To operate the steering system on a disabled truck, an Auxiliary Power Unit (APU) can be connected to the secondary steering connector (4) on the solenoid and relief valve manifold and to a suction port on the hydraulic tank (see Visual No. 133). The APU will provide supply oil to charge the accumulators. Steering capability is then available to tow the truck. The 785C has two accumulators (5). The steering system pressure tap (6) is located on the bottom of the left steering accumulator.
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SOLENOID AND RELIEF VALVE MANIFOLD
Text Reference
Supply From Pump
To / From Accumulators
To Steering Control Valve
To Tank
Bleed Down Solenoid Back-up Relief Valve
146
Shown is a sectional view of the solenoid and relief valve manifold. The accumulator bleed down solenoid is energized by the bleed down solenoid shutdown control (see Visual No. 154) when the key start switch is moved to the OFF position. The bleed down solenoid shutdown control holds the solenoid open for 70 seconds. Pressure oil from the accumulators is sensed by the bleed down solenoid. When the solenoid is ENERGIZED, the plunger moves and connects the pressure oil to the drain passage. Pressure oil flows through an orifice, past the plunger, to the tank. The orifice limits the return oil flow from the accumulators to a rate which is lower than the flow limit (restriction) of the steering oil filter in the hydraulic tank. When the solenoid is DE-ENERGIZED, spring force moves the plunger and pressure oil cannot go to drain.
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Text Reference
The back-up relief valve protects the steering system if the steering pump malfunctions (fails to destroke). Pressure oil from the steering pump works against the end of the back-up relief valve and the spring. The relief valve unseats (opens) if the pressure reaches approximately: 785C: 20700 ± 400 kPa (3000 ± 60 psi) at 8 ± 2 L/min (2 ± .5 gpm) 789C: 20670 ± 400 kPa (3000 ± 60 psi) at 8 ± 2 L/min (2 ± .5 gpm)
Oil then flows past the relief valve and drains to the tank. The back-up relief valve must be adjusted only on a test bench. The pressure setting of the back-up relief valve can be changed by adjusting the spring force that keeps the relief valve seated (closed). To change the relief valve setting, remove the protective cap and turn the adjustment screw clockwise to increase or counterclockwise to decrease the pressure setting. One revolution of the setscrew will change the pressure setting 3800 kPa (550 psi). A functional test of the back-up relief valve can be performed on the machine by installing a manual hydraulic pump at the location of the Auxiliary Power Unit (APU) connector and installing blocker plates to prevent oil from flowing to the accumulators. See the service manual for more detailed information. NOTE: Using the functional test procedure to adjust the back-up relief valve will provide only an approximate setting. Accurate setting of the back-up relief valve can only be performed on a hydraulic test bench.
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Text Reference
1
2
147
The steering directional valve (1) used on the 789C truck is pilot operated from the HMU in the operator’s station. Five pilot lines connect these two components. The pilot lines send pilot oil from the HMU to shift the spools in the steering directional valve. The spools control the amount and direction of pressure oil sent to the steering cylinders. Four pilot lines are used for pump supply, tank return, left turn, and right turn. The fifth pilot line is for the load sensing signal. When checking the steering system cut-out and cut-in pressures, a gauge can be connected at the pressure tap (2).
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Left Turn Cylinder
Text Reference
To Tank
Right Turn Cylinder
Relief / Makeup Valve
Back Pressure Valve
Relief / Makeup Valve
STEERING DIRECTIONAL VALVE NO TURN
Right Turn Pilot Oil
Left Turn Pilot Oil
Combiner / Check Spool
Amplifier Spool
Priority Spool Load Sensing Port From Accumulator
Hand Metering Unit Supply and Thermal Bleed
148
Shown is a sectional view of the steering directional valve. The main components of the steering directional valve are: the priority spool, the amplifier spool with internal combiner/check spool, the directional spool, the relief/makeup valves and the back pressure valve. Pressure oil from the accumulators flows past the spring biased priority spool and is blocked by the amplifier spool. The same pressure oil flows through an orifice to the right end of the priority spool. The orifice stabilizes the flow to the priority spool and must be present to open and close the priority spool as the flow demand changes. The same pressure oil flows to the HMU. After all the passages fill with pressure oil, the priority spool shifts to the left, but remains partially open. In this position, the priority spool allows a small amount of oil flow (thermal bleed) to the HMU and decreases the pressure to the HMU supply port. The "thermal bleed" prevents the HMU from sticking. With the truck in the NEUTRAL or NO TURN position, all four working ports (supply, tank, right turn, and left turn) are vented to the tank through the HMU. The directional spool is held in the center position by the centering springs.
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Text Reference
While the truck is traveling straight (no steer), any rolling resistance (opposition) acting on the steering cylinders creates a pressure increase. The increased pressure acts on the relief/makeup valve in that port. If the pressure increase exceeds 28000 ± 1000 kPa (4065 ± 150 psi), the relief poppet will open. A pressure drop occurs across the orifice. The pressure drop causes the dump valve to move and allows oil to flow to the tank passage. The relief action causes the makeup portion of the other relief/makeup valve to open and replenish oil to the low pressure ends of the cylinders. The excess (dumped) oil flows across the bac k pressure valve and enters the outer end of the other relief/makeup valve. A pressure difference of 48 kPa (7 psi) between the tank passage and the low pressure cylinder port causes the makeup valve to open. The excess oil flows into the low pressure cylinder port to prevent cavitation of the cylinder. The back pressure valve also prevents cavitation of the cylinders by providing a positive pressure of 170 kPa (25 psi) in the passage behind the makeup valve. A pressure higher than 170 kPa (25 psi) will open the back pressure valve to the tank. The steering directional valve must be removed and tested on a hydraulic test bench to accurately check the setting of the relief/makeup valves. A functional test of the relief/makeup valves can be performed on the machine by connecting a manual hydraulic pump and installing blocker plates to prevent oil from flowing to the steering cylinders. See the service manual for more detailed information. NOTE: Using the functional test procedure to adjust the relief/makeup valves will provide only an approximate setting. Accurate setting of the relief/makeup valves can only be performed on a hydraulic test bench.
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Left Turn Cylinder
Text Reference
To Tank
Right Turn Cylinder
Back Pressure Valve
Relief / Makeup Valve Relief/makeup Valve
STEERING DIRECTIONAL VALVE RIGHT TURN Right Turn Pilot Oil
Left Turn Pilot Oil
Combiner / Check Spool
Amplifier Spool
Priority Spool Load Sensing Port From Accumulator
Hand Metering Unit Supply and Thermal Bleed
149
When the steering wheel is turned to the RIGHT, the "thermal bleed" and venting of the four work ports to the tank is stopped. The increased supply pressure flows to the HMU and the load sensing pilot line. The load sensing pilot line directs cylinder pressure to the priority spool in the directional valve. Cylinder pressure is present in the HMU because pilot oil combines with accumulator oil in the combiner/check valve spool in the directional valve. The increased pressure in the load sensing line causes the priority spool to move to the right and allows more oil flow to the HMU through the supply line. The load sensing port supply pressure varies with the steering load. The priority spool moves proportionally, allowing sufficient oil flow to meet the steering requirements. Pilot oil flows through a stabilizing orifice to the right turn pilot p ort of the directional valve and moves the directional spool. Movement of the directional spool allows pilot oil to flow to the amplifier and combiner/check spools. The pilot oil divides at the amplifier spool. Pilot oil flows through a narrow groove around the combiner/check spool. The pilot oil is momentarily blocked until the amplifier spool moves far enough to the right to allow partial oil flow through one of eight orifices.
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Text Reference
Pilot oil also flows through a connecting pin hole and a stabilizing orifice to the left end of the amplifier spool and causes the amplifier spool to move to the right. Accumulator oil at the spring end (right end) of the amplifier spool flows through a mid-connecting pin to the left end of the amplifier spool and also causes the amplifier spool to move to the right. When the amplifier spool moves to the right, accumulator oil flows to the inner chamber, forcing the combiner/check spool to the left. Accumulator oil then flows through seven of the eight orifices. Pilot and accumulator oil combine. Oil flows across the directional spool (which has already shifted) for a RIGHT TURN. The faster the steering wheel is turned, the farther the directional spool and the amplifier spool are shifted. A higher flow rate is available, which causes the truck to turn faster. The ratio of pilot and pump supply oil that combine is always the same because one orifice is dedicated to pilot flow and seven orifices are dedicated to accumulator supply flow. Return oil from the cylinders flows across the directional spool, around the relief/makeup valve, forces the back pressure valve open and returns to the tank. During a turn, if a front wheel strikes a large obstruction that cannot move, oil pressure in that steering cylinder and oil line increases. Oil flow to the cylinder is reversed. This pressure spike is felt in the amplifier spool. The combiner/check spool moves to the right and blocks the seven pump supply oil orifices to the steering cylinders. The amplifier spool moves to the left and blocks the pilot oil orifice. Pilot oil flow to the steering cylinders stops. The pressure spike is not felt at the HMU. If the pressure spike is large enough, the relief/makeup valve drains the pressure oil to the tank as previously described.
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Text Reference
4 2
3 1
150
Shown is the solenoid and relief valve manifold (1) and the crossover relief valves (2) on the 785C truck. The crossover relief valves (2) are located in one housing mounted on the inside of the left frame rail near the front of the truck. The crossover relief valves prevent damage from high pressure oil in the steering cylinder circuit caused by an outside force applied to a front wheel when the steering wheel is stationary. The crossover relief valve housing contains two pressure taps (3) where steering system pressure can be measured. One tap shows pressure during a left turn and the other tap shows pressure during a right turn. To check the steering system pressure, turn the steering wheel completely in either direction. Operate the engine at LOW IDLE. Continue to turn the steering wheel after the wheels have stopped and the pressure will increase to the pump compensator valve setting. Check the steering pressure while turning in both directions. The pump compensator valve setting should be observed on the gauge in both directions. If the pressure readings are different, one of the crossover relief valve settings is probably incorrect. A misadjusted valve must be removed and readjusted on a test bench. On the 785C, one pressure switch (4) monitors the condition of the steering system. The switch provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to the VIMS.
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Text Reference
785C CROSSOVER RELIEF SYSTEM EXTERNAL IMPACT
Crossover Relief Valves
Hand Metering Unit
151
On the 785C truck, when the steering wheel is stationary, the HMU blocks oil in the steering cylinders and in the lines between the steering cylinders and the HMU. The oil blockage prevents the front wheels from moving when the steering wheel is not turned. If pressure is applied against the front wheels while the steering wheel is stationary, the pressure of the oil increases in the head end of one cylinder and the rod end of the other cylinder. If the increase of oil pressure exceeds 18270 kPa (2650 psi) at the affected crossover relief valve, the va lve will open. Oil from the high pressure ends of the steering cylinders then transfers to the low pressure ends of the cylinders.
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Text Reference
152
The 789C Hand Metering Unit (HMU) (arrow) is located at the base of the steering column behind a cover at the front of the cab. The HMU is connected to the steering wheel and controlled by the operator. The 789C HMU meters the amount of oil sent to the steering directional valve by the speed at which the steering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steering cylinders from the steering directional valve, and the faster the wheels will change direction. The 785C HMU is larger because oil flows directly from the HMU, through the crossover relief valve, to the steering cylinders. The capacity of the 785C HMU must be large enough to handle the flow required to fill the steering cylinders and allow satisfactory steering cycle times. On the front of the HMU are four ports: - Return to tank
- Left turn
- Pump supply
- Right turn
The 789C HMU has a fifth port on the side of the HMU. The fifth port is the load sensing signal line to the steering directional valve.
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Text Reference
1
2
153
Two steering accumulators (1) provide the supply oil during normal operation and temporary secondary steering if a loss of pump flow occurs (789C shown). Inside each accumulator is a rubber bladder that is charged with nitrogen. The nitrogen charge provides energy for normal steering and secondary steering capability if steering pump flow stops. To check the secondary steering system, the engine must be shut off with the manual engine shutdown switch (see Visual No. 25) while leaving the key start switch in the ON position. When the manual shutdown switch is used, the bleed down solenoid is not energized and the accumulators do not bleed down. The truck can then be steered with the engine stopped. The steering accumulator pressure switch (2) monitors the steering accumulator pressure. The switch provides an input to the VIMS. The VIMS refers to this switch as the "high steering pressure" switch.
WARNING High pressure oil remains in the accumulators if the manual shutdown switch is used. To release the oil pressure in the accumulators, turn the key start switch to the OFF position and turn the steering wheel left and right until the oil is drained from the accumulators (steering wheel can no longer be turned).
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Text Reference
154
Shown is the shutdown control (arrow) for the steering accumulator bleed down solenoid. The control is located in the compartment behind the cab. The steering accumulator bleed down solenoid is activated by the control when the key start switch is moved to the OFF position. The bleed down solenoid shutdown control holds the solenoid open for 70 seconds. The charge pressure for the steering accumulators is: 785C: 8270 ± 0 kPa (1200 ± 0 psi) 789C: 5512 ± 345 kPa (800 ± 50 psi)
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Text Reference
HOIST SYSTEM 789C
155
HOIST SYSTEM
The hoist system on the 785C and 789C trucks is electronically controlled by the Transmission/Chassis ECM. The hoist control system operates similarly to the earlier trucks. The four operating positions are: RAISE, HOLD, FLOAT, and LOWER. The hoist valve has a fifth position referred to as the SNUB position. The operator is unaware of the SNUB position because a corresponding lever position is not provided. When the body is being lowered, just before the body contacts the frame, the Transmission/Chassis ECM signals the hoist solenoids to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame. The hoist system can be enabled or disabled using ET. All trucks shipped from the factory without bodies installed are set at the Hoist Enable Status 2. The Hoist Enable Status 2 is a test mode only and will prevent the hoist cylinders from accidentally being activated. After the body is installed, change the Hoist Enable Status to 1 for the hoist system to function properly.
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Text Reference
156
The operator controls the hoist lever (arrow). The four positions of the hoist lever are RAISE, HOLD, FLOAT, and LOWER. The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist control valve will actually be in the SNUB position. If the transmission is in REVERSE when the bod y is being raised, the hoist lever sensor is used to shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until: 1. The hoist lever is moved into the HOLD or FLOAT position; and 2. the shift lever has been cycled into and out of NEUTRAL. NOTE: If the truck is started with the body raised and the hoist lever in FLOAT, the lever must be moved into HOLD and then FLOAT before the body will lower.
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Text Reference
157
The hoist lever controls a Pulse Width Modulated (PWM) position sensor (arrow). The PWM sensor sends duty cycle input signals to the Transmission/Chassis ECM. Depending on the position of the sensor and the corresponding duty cycle, one of the two solenoids located on the hoist valve is energized. The four positions of the hoist lever are RAISE, HOLD, FLOAT, and LOWER, but since the sensor provides a duty cycle signal that changes for all positions of the hoist lever, the operator can modulate the speed of the hoist cylinders. The hoist lever sensor also replaces the body raise switch (transmission neutralizer switch) that was located behind the operator's seat. The hoist lever sensor performs three functions: - Raises and lowers the body - Neutralizes the transmission in REVERSE - Starts a new TPMS cycle The hoist lever position sensor receives 24 Volts from the Transmission/ Chassis ECM. To check the supply voltage of the sensor, connect a multimeter between Pins A and B of the sensor connector. Set the meter to read "DC Volts." To check the output signal of the hoist lever position sensor, connect a multimeter between Pins B and C of the hoist lever position sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the sensor should be approximately 5 to 95% between full RAISE to full LOWER.
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Text Reference
3 1
2
158
Shown is the hoist, converter and brake oil hydraulic tank (1) and the oil level sight gauges (2). The oil level is normally checked with the upper sight gauge. The oil level should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running. The lower sight gauge is used when filling the hydraulic tank with the hoist cylinders in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge as explained above. Use only Transmission Drive Train Oil (TDTO) with a specification of TO-4 or newer. TDTO-4 oil: - Provides maximum frictional capability required for clutch discs used in the brakes. - Increases brake holding capability by reducing brake slippage. - Controls brake chatter. Check the hydraulic tank breather (3) for restriction. Clean the filter if it is restricted.
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Text Reference
159
Shown is the rear of the transmission and hoist hydraulic tank and the converter and brake oil hydraulic tank. The hoist system pumps pull oil from the hydraulic tank through the suction screens (arrows) located in the rear of the tan k.
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2
Text Reference
2 1
160
The hoist system oil for the "C" Series Trucks is supplied by a two-section pump (1) located at the top rear of the pump drive. Oil flows from the hoist pump through two screens to the hoist valve. The hoist system pressure can be tested at the two pressure taps (2). The hoist system relief pressures are different in the RAISE and LOWER positions. The hoist system relief pressure during RAISE is: 785C/789C: 17225 + 700 - 0 kPa (2500 + 100 - 0 psi) 789C (with cast iron pump): 18960 ± 345 (2750 ± 50 psi)
The hoist system relief pressure during LOWER is: 785C/789C: 3450 + 350 - 0 kPa (500 + 50 - 0 psi)
When the body is in the DOWN position, the hoist valve will be in the SNUB position. The body position sensor rod must be disconnected from the body and the sensor must be rotated to the RAISE position before the LOWER relief pressure can be tested. In the HOLD, FLOAT, and SNUB positions, the gauge will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes, and hoses (normally much lower than the actual oil cooler relief valve setting). The maximum pressure is limited by the oil cooler relief valve, which has a setting of 790 ± 20 kPa (115 ± 3 psi).
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1
Text Reference
2
161
Oil flows from the hoist pump through the hoist screens (1) to the hoist control valve. Two hoist screen bypass switches (2) provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the ope rator if the hoist screens are restricted.
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2
Text Reference
3
4
1 5
6
162
Oil flows from the hoist pump through two ports (1) (only one visible in this view) to the hoist control valve located inside the right frame next to the hoist cylinder. Two load check valves, one for each pump port, are located below the two plugs (2). The load check valves remain closed until the pump supply pressure is higher than the pressure in the hoist cylinders. The load check valves prevent the body from dropping before the RAISE pressure increases. The hoist system relief pressures are different in the RAISE and LOWER positions. The RAISE relief valve (3) controls the pressure in the hoist system during RAISE. The LOWER relief valve (4) controls the pressure in the hoist system during LOWER. The relief valve housing must be removed to install shims (see Visual No. 164). Oil flows through the drain port (5) to the hydraulic tank. When the hoist valve is in the HOLD, FLOAT, or SNUB position, all the hoist pump oil flows through two ports (6), one on each side of the hoist valve, to the two rear brake oil coolers located on the right side of the engine.
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Text Reference
4 6
5
7
1
2
3
163
A counterbalance valve (1) is mounted on the left side of the hoist valve. The counterbalance valve prevents cavitation of the cylinders when the body raises faster than the pumps can supply oil to the cylinders (caused by a sudden shift of the load). The counterbalance valve signal pressure can be checked at the test port (2) by removing the plug and installing a pressure tap. The counterbalance signal pressure is equal to the RAISE pressure. An oil cooler relief valve is located behind the large plug (3). The oil cooler relief valve limits the rear brake oil cooling pressure when the hoist valve is in the HOLD, FLOAT, or SNUB position. The setting of the oil cooler relief valve is 790 kPa (115 psi). The hoist valve uses parking brake release pressure as the pilot oil to shift the d irectional spool inside the hoist valve. The parking brake release pressure is 4700 ± 200 kPa (680 ± 30 psi). Pilot pressure is always present at both ends of the directional spool. Two solenoid valves are used to drain the pilot oil from the ends of the directional spool, which then allows the spool to move. On the left is the RAISE solenoid valve (4), and on the right is the LOWER solenoid valve (5). The RAISE and LOWER solenoid valves are always receiving approximately 300 millivolts at a frequency of 80 Hz when they are in any position except HOLD. The excitation, referred to as "dither," is used to keep the solenoids in a ready state for quick response.
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Text Reference
When the Transmission/Chassis ECM receives an input signal from the hoist lever sensor, the Transmission/Chassis ECM sends an output signal current between 0 and 1.9 amps to one of the solenoids. The amount of current sent to the solenoid determines the amount of pilot oil that is drained from the end of the directional spool and, therefore, the distance that the directional spool travels toward the solenoid. Oil flows through two upper ports (6), one o n each side of the hoist valve, to RAISE the hoist cylinders. Oil flows through two lower ports (7), one on each side of the hoist valve, to LOWER the hoist cylinders.
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Text Reference
Lower Solenoid
Parking Brake Release Pressure
"C" SERIES HOIST CONTROL VALVE HOLD
Rear Brake Oil Cooler Relief Valve
To Tank
To Hoist Cylinder Head End
Load Check Valve
To Hoist Cylinder Rod End
Low Pressure Relief Valve High Pressure Relief Valve
Rod End Vent Slot
Counterbalance Valve To Rear Brake Oil Coolers
Dual Stage Relief Valve Signal Stem
Main Relief Dump Spool
Pump Supply Port
Parking Brake Release Pressure
Raise Solenoid
164
Shown is a sectional view of the hoist valve in the HOLD position. Pilot oil pressure is directed to both ends of the directional spool. The spool is held in the centered position by the centering springs and the pilot oil. Passages in the directional spool vent the dual stage relief valve signal stem to the tank. All the hoist pump oil flows through the rear brake oil coolers to the rear brakes. The position of the directional spool blocks the oil in the head end of the hoist cylinders. Oil in the rod end of the hoist cylinders is connected to the rear brake cooling oil by a small vent slot cut in the directional spool. A gauge connected to the hoist system pressure taps while the hoist valve is in the HOLD position will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes, and hoses (normally much lower than the actual oil cooler relief valve setting). The maximum pressure in the circuit should correspond to the setting of the rear brake oil cooler relief valve. The setting of the oil cooler relief valve is 790 kPa (115 psi).
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Text Reference
Lower Solenoid
"C" SERIES HOIST CONTROL VALVE
Parking Brake Release Pressure
RAISE
Rear Brake Oil Cooler Relief Valve
To Tank
To Hoist Cylinder Head End
Load Check Valve
From Hoist Cylinder Rod End
Low Pressure Relief Valve High Pressure Relief Valve
Rod End Vent Slot
Dual Stage Relief Valve Signal Stem
Main Relief Dump Spool
Counterbalance Valve To Rear Brake Oil Coolers
Pump Supply Port
Parking Brake Release Pressure
Raise Solenoid
On
165
Shown is a sectional view of the hoist valve in the RAISE position. The RAISE solenoid is energized and drains pilot oil pressure from the lower end of the directional spool. The directional spool moves down. Pump oil flows past the directional spool to the head end of the hoist cylinders. When the directional spool is initially shifted, the two load check valves (one shown) remain closed until the pump supply pressure is higher than the pressure in the hoist cylinders. The load check valves prevent the body from dropping before the RAISE pressure increases. The directional spool also sends hoist cylinder raise pressure to the dual stage relief valve signal stem and the counterbalance valve. The dual stage relief valve signal stem moves down and blocks the supply pressure from opening the low pressure relief valve.
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Text Reference
The counterbalance valve is held open by the hoist cylinder raise pressure. Oil from the rod end of the hoist cylinders flows freely to the rear brake oil coolers. If the body raises faster than the pump can supply oil to the hoist cylinders (caused by a sudden shift of the load) and the raise pressure drops below 2275 kPa (330 psi), the counterbalance valve starts to close and restricts the flow of oil from the rod end of the hoist cylinders. Restricting the flow of oil from the rod end of the hoist cylinders will slow down the cylinders and prevent cavitation. Cavitation in the hoist cylinders can cause the body to drop suddenly when the hoist lever is moved from the RAISE position to the LOWER position. The pressure in the head end of the hoist cylinders cannot exceed: 785C/789C: 17225 + 700 - 0 kPa (2500 + 100 - 0 psi) 789C (with cast iron pump): 18960 ± 345 (2750 ± 50 psi)
The high pressure relief valve will open if the pressure increases above this specification. When the high pressure relief valve opens, the dump spool moves to the left, and pump oil is directed to the rear brake oil coolers. The high pressure hoist relief valve setting is checke d at the two pressure taps located on the hoist pump. Check the relief pressures with the hoist lever in the RAISE position and the engine at HIGH IDLE.
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Text Reference
HOIST COUNTERBALANCE VALVE
Head End Signal Pressure From Pump
To Tank
From Hoist Cylinder Rod End
Rod End Pressure Piston
To Hoist Cylinder Rod End
RAISE
Check Valve
LOWER AND FLOAT
166
During RAISE, the counterbalance valve prevents the dump body from running ahead of the hoist pumps if the load shifts rapidly to the rear of the body and attempts to pull the hoist cylinders. Signal pressure from the head end of the hoist cylinders holds the counterbalance valve open. Oil from the rod end of the hoist cylinders flows unrestricted through the counterbalance valve to the tank. If the head end pressure decreases below 2270 kPa (330 psi), the counterbalance valve moves down and restricts the flow of oil from the rod end of the cylinders to the tank. If no head end signal pressure is present, rod end pressure can still open the counterbalance valve. If the rod end pressure exceeds 6900 ± 690 kPa (1000 ± 100 psi) at the rod end pressure piston, the valve will move up and allow rod end oil to flow from the cylinders to the tank. During LOWER and FLOAT, the counterbalance valve allows unrestricted flow from the pump through a check valve to the rod end of the hoist cylinders.
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Lower Solenoid
Text Reference
On
Parking Brake Release Pressure
"C" SERIES HOIST CONTROL VALVE LOWER (POWER DOWN)
Rear Brake Oil Cooler Relief Valve
To Tank
From Hoist Cylinder Head End
Load Check Valve
To Hoist Cylinder Rod End
Low Pressure Relief Valve High Pressure Relief Valve
Rod End Vent Slot
Counterbalance Valve To Rear Brake Oil Coolers
Dual Stage Relief Valve Signal Stem
Main Relief Dump Spool
Pump Supply Port
Parking Brake Release Pressure
Raise Solenoid
167
Shown is a sectional view of the hoist valve in the LOWER (power down) position. The LOWER solenoid is energized and drains pilot oil pressure from the upper end of the directional spool. The directional spool moves up. Supply oil from the pump flows past the directional spool, through the counterbalance valve, to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The supply oil in the rod end of the cylinders and the weight of the body move the cylinders to their retracted positions. Just before the body contacts the frame, the body position sensor sends a signal to the Transmission/Chassis ECM to move the valve spool to the SNUB position. In the SNUB position, the valve spool moves slightly to restrict the flow of oil and lower the body gently. The directional spool also vents the passage to the dual stage relief valve signal stem. The dual stage relief valve signal stem allows supply pressure to be limited by the low pressure relief valve.
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Text Reference
If the pressure in the rod end of the hoist cylinders exceeds 3450 + 350 - 0 kPa (500 + 50 - 0 psi), the low pressure relief valve will open. When the low pressure relief valve opens, the dump spool moves to the left and pump oil flows to the rear brake oil coolers. The low pressure hoist relief valve setting is checked at the two pressure taps located on the hoist pump. Check the relief pressures with the hoist lever in the LOWER position and the engine at HIGH IDLE. When the body is in the DOWN position, the hoist valve will be in the SNUB position. The body position sensor rod must be disconnected from the body, and the sensor must be rotated to the RAISE position before the LOWER relief pressure can be tested.
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Lower Solenoid
Text Reference
On
Parking Brake Release Pressure
"C" SERIES HOIST CONTROL VALVE FLOAT
Rear Brake Oil Cooler Relief Valve
To Tank
From Hoist Cylinder Head End
Load Check Valve
To Hoist Cylinder Rod End
Low Pressure Relief Valve High Pressure Relief Valve
Rod End Vent Slot
Counterbalance Valve To Rear Brake Oil Coolers
Dual Stage Relief Valve Signal Stem
Main Relief Dump Spool
Pump Supply Port
Parking Brake Release Pressure
Raise Solenoid
168
Shown is a sectional view of the hoist valve in the FLOAT position. The LOWER solenoid is partially energized and drains part of the pilot oil pressure above the directional spool to the tank. The directional spool moves up. Because the pilot pressure is only partially drained, the directional spool does not move as far up as during LOWER. Pump supply oil flows past the directional spool, through the counterbalance valve, to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The directional valve is in a position that permits the pressure of the oil flowing to the rear brake oil coolers to be felt at the rod end of the hoist cylinders. The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not the hoist cylinders. The hoist valve will actually be in the SNUB position. Just before the body contacts the frame, the body position sensor sends a signal to the Transmission/Chassis ECM to move the valve spool to the SNUB position. In the SNUB position, the valve spool moves slightly to restrict the flow of oil and lower the body gently.
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Text Reference
169
Shown are the twin two-stage hoist cylinders used to raise and lower the body. Check the condition of the body pads (arrow) for wear or damage. To LOWER the body with a dead engine, hoist pilot pressure is required. The towing pump can be used to provide the hoist pilot oil. To lower the body with a dead engine: - Turn ON the key start switch so the towing motor and the hoist solenoids can be energized. - Move the hoist lever to the RAISE position for 15 seconds, then to the FLOAT position. - Depress the brake retraction switch on the dash (see Visual No. 48). To RAISE the body with a dead engine, connect an Auxiliary Power Unit (APU) to the hoist cylinders. Follow the same procedure used to lower the body with a dead engine, except keep the hoist lever in RAISE after the 15 seconds interval. NOTE: For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).
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Text Reference
170
The hoist system pumps pull oil from the hydraulic tank through suction screens. Oil flows from the hoist pump through the hoist screens to the hoist control valve. The hoist valve uses parking brake release pressure as pilot oil to shift the directional spool inside the hoist valve. Two solenoid valves are used to drain the pilot oil from the ends of the directional spool. The solenoid valve on the left is energized in the RAISE position. The solenoid valve on the right is energized in the LOWER or FLOAT position. When the hoist valve is in the HOLD or FLOAT position, all the hoist pump oil flows through the rear brake oil coolers to the rear brakes. An oil cooler relief valve is located in the hoist valve. The relief valve limits the rear brake oil cooling pressure when the hoist valve is in the HOLD or FLOAT position. Two hydraulic cylinders are used to raise the body away from the frame of the truck. When the hoist lever is held in the RAISE position, supply oil flows to the head end of the hoist cylinders and moves the two stage cylinders to their extended lengths. The oil from the rod end of the cylinders flows through the hoist valve to the rear brake oil cooling circuit.
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Text Reference
When the hoist lever is moved to the LOWER or FLOAT position and the cylinders are extended, supply oil enters the rod end of the hoist cylinders and lowers the second stage of the cylinders. The oil from the head end of the cylinders flows through the hoist valve to the hydraulic tank.
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Text Reference
AIR SYSTEM AND BRAKES 789C
171
AIR SYSTEM AND BRAKES
Two separate brake systems are used on the "C" Series trucks. The two brake systems are: the parking/secondary brake system and the service/retarder brake system. The parking/secondary brakes are spring engaged and hydraulically released. The service/retarder brakes are engaged hydraulically by an air-over-oil brake system. The "C" Series trucks are also equipped with an air system. An engine driven air compressor supplies the air and fills two tanks. Air from the tanks provides energy to perform several functions: - Engine start-up - Service and retarder brake control - Secondary and parking brake control - Automatic lubrication injection (grease) - Horn, air seat, and cab clean-out
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Text Reference
172
Shown is a cutaway illustration of an oil cooled brake assembly. The brakes are environmentally sealed and adjustment free. Oil continually flows through the brake discs for cooling. Duo-Cone seals prevent the cooling oil from leaking to the ground or transferring into the axle housing. The wheel bearing adjustment must be maintained to keep the Duo-Cone seals from leaking. The smaller piston (yellow) is used to ENGAGE the secondary and parking brakes. The parking brakes are spring ENGAGED and hydraulically RELEASED. The larger piston (purple) is used to ENGAGE the retarder/service brakes. The retarder/service brakes are engaged hydraulically by an air-over-oil brake system.
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Text Reference
173
Air Charging System
The air system is charged by an air compressor mounted on the left front of the engine. System pressure is controlled by the governor (arrow). The governor maintains the system pressure between 660 and 830 kPa (95 and 120 psi). The governor setting can be adjusted with a screw below the cover on top of the governor. Turn the adjustment screw OUT to increase the pressure and IN to decrease the pressure. The capacity of the air charging system has been increased. The air compressor has been increased from a two-cylinder compressor to a four-cylinder compressor. To handle the increased air flow, two larger air dryers are used, and the hoses and tubing h ave also been increased in size. To test the air compressor efficiency, lower the air system pressure to 480 kPa (70 psi). Start the engine and raise the engine speed to HIGH IDLE. When the air system pressure reaches 585 kPa (85 psi), measure the time that it takes to build system pressure from 585 kPa (85 psi) to 690 kPa (100 psi). The time to raise the pressure should be 50 seconds or less. If the time recorded is greater than 50 seconds, check for leaks or a restriction in the system. If no leaks or restrictions are found, the air compressor may have a problem.
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Text Reference
1
2
174
On the 789C truck, air flows from the air compressor to two air dryers (1) located behind the left front tire. The 785C has two air dryers located in front of the left front suspension cylinder. The air system can be charged from a remote air supply through a ground level connector (2) inside the left frame. The air dryers remove contaminants and moisture from the air system. The condition of the desiccant in the air dryers should be checked every 250 hours and changed periodically (determined by the humidity of the local climate). When the air compressor governor senses that system air pressure is at the cut-out pressure of 830 kPa (120 psi), the governor sends an air pressure signal to the purge valve in the bottom of the dryers. The purge valve opens and air pressure that is trapped in the air dryers is exhausted through the desiccant, an oil filter and the purge valve. An air system relief valve is located on the air dryers to protect the system if the air compressor governor malfunctions. A heating element in the bottom of the dryers prevents moisture in the dryers from freezing in cold weather.
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Text Reference
1
2
175
Air flows through the air dryers and fills two tanks. The service/retarder brake tank (1) is located on the right platform. This tank also supplies air for the air start system. The second tank is located behind the cab and supplies air for the parking/secondary brake system. Condensation should be drained from the tank daily through the drain valve (2). A relief valve located near the tank drain is installed in the service/retarder brake tank. This relief valve protects the air system when the air dryers have exhausted and the ball check valves in the air dryer outlet ports close. The check valves separate the air system from the air dryer relief valves.
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Text Reference
1
2
176
Located behind the operator’s station is a pressure protection valve (1). Supply air flows from the large service/retarder brake tank, through the p ressure protection valve, to the secondary a ir system and accessories. The pressure protection valve opens at 550 kPa (80 psi) and closes at 482 kPa (70 psi). If the secondary air lines or an accessory circuit fails, the pressure protection valve maintains a minimum of 482 kPa (70 psi) in the service/retarder brake circuit. To test the pressure protection valve, drain the air pressure to approximately 345 kPa (50 psi). Use the VIMS display to observe the brake air pressure. With the engine running at LOW IDLE, press the horn button. Record the air pressure when the horn sounds. This pressure reading is the open setting of the pressure protection valve. Slowly drain the air pressure and record the air pressure when the horn turns off. This pressure reading is the setting of the pressure protection valve when it closes. The air system pressure sensor (2) provides an input signal to the Brake ECM. The Brake ECM sends a signal to the VIMS, which informs the operator if a problem exists in the air system. Also located behind the operator’s station are the service/retarder brake switch, the parking/secondary brake switch and the brake light switch (see Visual No. 128).
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Text Reference
177
The solenoid air valve (arrow) provides a controlled air supply for the automatic lubrication (grease) system. The solenoid air valve is controlled by the VIMS. The VIMS ENERGIZES the solenoid ten minutes after the machine is started. The VIMS keeps the solenoid ENERGIZED for 75 seconds and then DE-ENERGIZES it. Every 60 minutes thereafter, the VIMS ENERGIZES the solenoid for 75 seconds until the machine is stopped (turned off). These settings are adjustable through the VIMS keypad in the cab.
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Text Reference
178
Located behind the operator’s station is the parking/secondary brake air tank. A drain valve is located on the right side of the cab. Moisture should be drained from the tank daily through the drain valve (see Visual No. 33). A check valve (arrow) prevents a loss of air if an air line breaks upstream of the air tank.
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Text Reference
789C AIR CHARGING SYSTEM Air Compressor and Governor Air Dryers
To Air Start Solenoid Remote Supply Service / Retarder Brake Tank Low Air Sensor
To Auto Lube Solenoid To Horn / Seat / Clean-out Pressure Protection Valve Parking / Secondary Brake Tank
179
This schematic shows the flow of air through the 789C air charging system. Air flows from the air compressor, through the two air dryers, to the service/retarder brake tank. The 785C air charging system is the same as the 789C, but has only one air dryer. Air from the service/retarder brake tank enters the pressure protection valve. When the pressure in the service/retarder tank reaches 550 kPa (80 psi), the pressure protection valve allows air to flow to the parking/secondary brake tank, the air start system, the automatic lubrication system, and the accessory circuits (horn, air seat, and cab clean-out). All tanks have a check valve at the air supply port to prevent a loss of air if a leak upstream of the tank occurs.
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Text Reference
180
Brake Systems
The manual retarder valve (arrow) is controlled by the retarder lever in the cab. Normally, the retarder valve blocks air flow to the service brake relay valve near the brake master cylinders and to the front brake oil cooler diverter valve. When the retarder lever is pulled down, air flows to the service brake relay valve and the front brake oil cooler diverter valve [maximum pressure is approximately 550 kPa (80 psi)]. The retarder lever is used to modulate the service brake engagement by metering the amount of air flow to the service brake relay valve. The retarder engages the same brakes as the service brake pedal (see Visual No. 43), but is easier to control for brake modulation. The retarder system allows the machine to maintain a constant speed on long downgrades. The retarder will not apply all of the normal braking capacity.
NOTICE Do not use the retarder control as a parking brake or to stop the machine.
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Text Reference
4 2 5
3
1
8
7
6
181
The service brake valve (1) is controlled by the brake pedal in the cab. Supply air for the service brake valve, the manual retarder valve, and the Automatic Retarder Control (ARC) valve (2) is supplied from the manifold (3). When the service brakes are engaged, air flows from the service brake valve to the service brake relay valve near the brake master cylinders and to the front brake oil cooler diverter valve [maximum pressure is 825 kPa (120 psi)]. The service brake valve engages the same brakes as the retarder, but does not control brake modulation as precisely as the retarder. Air from the service brake valve and the manual retarder valve flows through the double check valve (4) to the service brake relay valve and through the double check valve (5) to the front brake oil cooler diverter valve. If the manual retarder and the service brakes are engaged at the same time, air from the system with the highest pressure will flow through the double check valves to the service brake relay valve and to the front brake oil cooler diverter valve. Air from the manual retarder valve also flows through the double check valve (6) to the retarder switch (7). The retarder switch turns on the amber retarder lamp on the dash in the operator’s station when the manual retarder is ENGAGED (see Visual No. 47).
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Text Reference
The function of the Automatic Retarder Control (ARC) system is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed. When the ARC is engaged, air flows from the ARC valve to a separate ARC relay valve located near the brake master cylinders. Air also flows from the ARC valve through the double check valve (6), to the retarder switch (7), and through double check valve (5) to the front brake oil cooler diverter valve. The brake light switch and the service/retarder brake switch (see Visual No. 128) are located in the supply line to the front brake oil cooler diverter valve (see Visual No. 102). The service brake valve, the manual retarder valve, and the Automatic Retarder Control (ARC) valve send air to these switches when engaged. The secondary brake valve (8) is controlled by the red pedal in the cab (see Visual No. 43). When the secondary brakes are engaged, air flows from the secondary brake valve to the signal port of an inverter valve (see next visual). The inverter valve then blocks the flow of air from the secondary brake tank to the brake release valve (see Visual No. 183). Blocking the air from the brake release valve positions the spool in the brake release valve to drain the oil from the parking brakes, which allows the springs in the parking brake to ENGAGE the brakes. The secondary brake valve can be used to modulate parking brake engagement by metering the amount of air flow to the brake release valve. The parking brake air valve (see Visual No. 44) on the shift console in the cab also controls the flow of air to the brake release valve, but the parking brake air valve does not modulate the parking brake application. The parking/secondary brake switch (see Visual No. 128) is located in the supply line to the brake release valve. The secondary brake valve and the parking brake air valve send air to this switch when engaged. INSTRUCTOR NOTE: The ARC system will be discussed in more detail later in this presentation.
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Text Reference
2
1
182
When the secondary brakes are engaged, air flows from the secondary brake valve to the signal port (1) of the inverter valve (2). The inverter valve then blocks the flow of air from the secondary brake tank to the brake release valve. Blocking the air from the brake release valve positions the spool in the brake release valve to drain the oil from the parking brakes, which allows the springs in the parking brake to ENGAGE the brakes.
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2
Text Reference
1
5 4 3
183
Oil from the parking brake release pump (see Visual No. 98) flows through the parking brake release filter (see Visual No. 101) to the brake release valve (1) located inside the left frame near the torque converter. Oil flows from the parking brake release valve to the parking brake piston in the brakes when the parking brakes are released. Supply air from the parking brake air valve in the cab or the secondary brake valve flows through the small hose (2) to an air chamber in the brake release valve. The brake release valve contains an air piston that moves a spool. The spool either directs oil to RELEASE the parking brakes or drains oil to ENGAGE the parking brakes. A relief valve (3) in the brake release valve limits the system pressure for releasing the brakes. The setting of the relief valve is 4700 ± 200 kPa (680 ± 30 psi). Supply oil flows from the brake release valve through an orifice and a screen (4) to the brake oil makeup tank. To release the parking brakes for service work or towing, the electric motor that turns the towing pump (5) can be energized by the brake release switch located in the cab (see Visual No. 48). The pump sends oil to the brake release valve to RELEASE the parking brakes. Towing pump pressure is controlled by a relief valve in the towing pump.
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Text Reference
TOWING SYSTEM
From Cab Secondary or Parking Brake Valve
Relief Valve
Parking Brake Release Pump
To TC Lockup Valve Parking Brake Release Filter
To Hoist Pilot System
Parking Brake Release Valve
Check Valve
Towing Pump and Motor
Towing Pump Relief Valve
184
Normally, supply oil flows from the parking brake release pump, through the parking brake release filter, to the parking brake release valve. If air pressure is present from the parking brake air valve or the secondary brake valve, supply oil flows past the relief valve, the check valve, and the spool to RELEASE the parking brakes. The relief valve limits the system pressure for releasing the brakes, torque converter lockup, and for the pilot oil to shift the hoist valve. The setting of the relief valve in the parking brake valve is 4700 ± 200 kPa (680 ± 30 psi). This schematic shows the flow of oil through the parking brake release system when the towing system is activated. Oil flow from the parking brake release pump has stopped. The towing motor is energized, and air pressure is present above the parking brake release valve piston. The air pressure moves the spool in the parking brake release valve down to block the drain port. Oil flows from the towing pump to the parking brake release valve and the parking brakes. The check valve to the right of the parking brake release filter blocks the oil from the towing pump from flowing to the parking brake release pump.
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Text Reference
During towing, the parking brake release pressure is limited by a relief valve in the towing pump. When the relief valve opens, oil transfers from the pressure side to the suction side of the towing pump. The setting of the relief valve is approximately 4480 kPa (650 psi). A check valve in the outlet port of the towing pump prevents oil from flowing to the towing pump during normal operation. To check the brake release system used for towing, connect a gauge to the parking brake release pressure tap on the rear axle (see Visual No. 189). Use a long gauge hose so the gauge can be held in the cab. With the parking brake air valve in the RELEASE position and the key start switch in the ON position, energize the parking brake release switch used for towing (on the dash). The parking brake release pressure should increase to 4480 kPa (650 psi). Turn off the switch when the pressure stops increasing. The parking brake release pressure must increase to a minimum of 3790 kPa (550 psi). The parking brakes start to release between 3100 and 3445 kPa (450 and 500 psi). During towing, the brake release switch on the dash must be energized whenever the parking brake release pressure decreases below this level or the brakes will drag. The parking brakes are fully released between 3445 and 3860 kPa (500 and 560 psi). A minimum of 550 kPa (80 psi) air pressure must be available at the parking brake release valve to ensure full release of the brakes for towing.
NOTE:
NOTICE Activate the brake release switch only when additional pressure is required to release the brakes. Leaving the brake release (towing) motor energized continuously will drain the batteries. The parking brake release pressure setting must not exceed 5445 kPa (790 psi). Exceeding this pressure can cause internal damage to the brake assembly.
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Text Reference
PARKING / SECONDARY BRAKES SECONDARY BRAKES RELEASED PARKING BRAKES ENGAGED
Parking Brake Valve
Secondary Brake Valve
Parking / Secondary Brake Switch
Parking Brake Release Pump
Parking Brake Release Valve
Inverter Valve To TC Lockup Valve and Hoist Pilot System
Parking / Secondary Brake Tank
185
Shown is the parking/secondary brake hydraulic and air system with the secondary brakes RELEASED and the parking brakes ENGAGED. Supply air from the parking/secondary brake air tank flows to the secondary brake valve and is blocked from flowing to the inverter valve signal port. Supply air is allowed to flow through the inverter valve and is blocked by the parking brake air valve. No air pressure is present to move the spool in the parking brake release valve. Supply oil from the parking brake release pump is blocked by the spool. Oil from the parking brake is open to drain through the parking brake release valve, which allows the springs in the parking brake to ENGAGE the brakes. A parking/secondary brake switch is located in the air line between the parking brake valve and the parking brake release valve. The switch provides an input signal to the Transmission/Chassis ECM. When the parking or secondary brakes are ENGAGED, the switch signals the Transmission/Chassis ECM to allow rapid downshifts.
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5
2
Text Reference
1
4
6 3
3
186
The front service brake relay valve (1) receives metered air from only the service brake valve or the manual retarder valve. The rear Automatic Retarder Control (ARC) brake relay valve (2) receives metered air from only the ARC valve. When the service brakes or manual retarder brakes are ENGAGED, the front relay valve opens and metered air flows from the service brake tank, through the double check valves (3), to the three brake cylinders (4). The brake relay valves reduce the time required to engage and release the brakes. The double check valves (3) are used to separate the service and manual retarder brakes from the ARC brake system. When the ARC brake system is ENGAGED, the rear relay valve opens and metered air flows from the service brake tank, through a pressure protection valve (5) and the double check valves (3), to the three brake cylinders (4). The pressure protection valve prevents a total loss of air pressure in the service brake air system if the ARC relay valve fails. The protection valve opens to send flow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreases below 310 kPa (45 psi). The brake cylinders operate by air-over-oil. When the metered air enters the brake cylinders, a piston moves down and pressurizes the oil in the bottom of the cylinders. One brake cylinder supplies oil to the front brakes through the slack adjuster (6). Two brake cylinders supply oil to the rear brakes through a separate slack adjuster.
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Text Reference
1
4
5
3
2
187
As the brake discs in the brake assemblies wear, more oil is needed from the brake cylinders to compensate for the wear. The brake makeup oil tank (1) supplies makeup oil for the brake cylinders. Oil from the parking brake release valve flows through an orifice and the screen (2) to provide a continuous supply of oil to the makeup tank. Low flow to the makeup tank can cause the makeup oil reserve to decrease and cause the brake cylinders to overstroke. To check for makeup oil flow, remove the cover from the makeup oil tank. With the engine at HIGH IDLE, a stream of oil filling the tank should be visible. If a stream of oil is not visible, the filter or hose to the tank may be restricted or pump flow may be low. Keep the service brake ENGAGED for at least one minute. If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke and cause an indicator rod to extend and open the brake overstroke switch (3). The switch provides an input signal to the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs the operator of the condition of the service/retarder brake oil circuit. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning. Front brake oil pressure can be measured at the pressure tap (4) located on the front brake slack adjuster.
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Text Reference
The oil-to-air ratio of the brake cylinder is approximately 6.6 to 1. To test the brake cylinder, install a gauge in the fitting on top of the brake cylinder and a gauge on the pressure tap on the slack adjuster. When the service brakes are ENGAGED, if the air pressure in the brake cylinder is 690 kPa (100 psi), the oil pressure measured at the slack adjuster should be approximately 4560 kPa (660 psi). When the brakes are RELEASED, both pressures should return to zero. Inspect the condition of the breather (5) for the brake cylinders. Oil should not leak from the breathers. Oil leaking from the breathers is an indication that the oil piston seals in the brake cylinder need replacement. Air flow from the breathers during a brake application is an indication that the brake cylinder air piston seals need replacement.
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Text Reference
BRAKE CYLINDER BRAKES ENGAGED Air Piston
Indicator Rod
From Makeup Tank
Oil Piston
To Slack Adjuster
Air Inlet
Breather Port Spring
Valve
Rod
188
This visual shows a sectional view of the brake cylinder when the brakes are ENGAGED. Air pressure from the brake relay valve enters the air inlet. The air pressure moves the air piston and the attached rod closes the valve in the oil piston. When the valve in the oil piston is closed, the oil piston pressurizes the oil in the cylinder. The pressure oil flows to the slack adjuster. If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke, which causes the indicator rod to extend and open the brake overstroke switch. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning. When the air pressure is removed from behind the air piston, the spring moves the air piston and the attached rod opens the valve in the oil piston. Any makeup oil that is needed flows into the passage at the top of the oil chamber, through the valve, and into the oil chamber at the right of the oil piston.
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3
2
Text Reference
3
1
189
The truck is equipped with two slack adjusters--one for the front brakes and one for the rear brakes. The slack adjuster (1) shown is for the rear brakes. The slack adjusters compensate for brake disc wear by allowing a small volume of oil to flow through the slack adjuster and remain between the slack adjuster and the brake piston under low pressure. The slack adjusters maintain a slight pressure on the brake piston at all times. Brake cooling oil pressure maintains a small clearance between the brake discs. The service brake oil pressure can be measured at the two taps (2) located on top of the slack adjusters. Air can be removed from the service brakes through two remote bleed valves (not shown) mounted on the rear axle housing. The parking brake release pressure can be measured at the two taps (3) on the axle housing. NOTE: Air can be removed from the front service brakes through bleed valves located on each wheel.
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Text Reference
BRAKE SLACK ADJUSTER Oil Flow To Brake Cylinder
Oil Flow From Brake Cylinder Small Piston
From Wheel Brakes
Large Piston
From Wheel Brakes
To Wheel Brakes To Wheel Brakes
BRAKES ENGAGED
BRAKES RELEASED
190
This visual shows sectional views of the slack adjuster when the brakes are RELEASED and ENGAGED. When the brakes are ENGAGED, oil from the brake cylinders enters the slack adjusters and the two large pistons move outward. Each large piston supplies oil to one wheel brake. The large pistons pressurize the oil to the service brake pistons and ENGAGE the brakes. Normally, the service brakes are FULLY ENGAGED before the large pistons in the slack adjusters reach the end of their stroke. As the brake discs wear, the service brake piston will travel farther to FULLY ENGAGE the brakes. When the service brake piston travels farther, the large piston in the slack adjuster moves farther out and contacts the end cover. The pressure in the slack adjuster increases until the small piston moves and allows makeup oil from the brake cylinders to flow to the service brake piston. When the brakes are RELEASED, the springs in the service brakes push the service brake pistons away from the brake discs. The oil from the service brake pistons pushes the large pistons in the slack adjuster to the center of the slack adjuster. Makeup oil that was used to ENGAGE the brakes is replenished at the brake cylinders from the makeup tank.
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Text Reference
The spring behind the large piston causes some oil pressure to be felt on the service brake piston when the brakes are RELEASED. Keeping some pressure on the brake piston provides rapid brake engagement with a minimum amount of brake cylinder piston travel. The slack adjusters can be checked for correct operation by opening the service brake bleed screw with the brakes RELEASED. A small amount of oil should flow from the bleed screw when the screw is opened. The small flow of oil verifies that the spring behind the large piston in the slack adjuster is maintaining some pressure on the service brake piston. Another check to verify correct slack adjuster operation is to connect a gauge to the pressure tap on top of the slack adjuster and another gauge at the service brake bleed screw location. With system air pressure at maximum and the service brake pedal depressed, the pressure reading on both gauges should be approximately the same. When the brakes are RELEASED, the pressure at the slack adjuster should return to zero. The pressure at the service brake bleed screw location should return to the residual pressure held on the brakes by the slack adjuster piston. The residual pressures at the service brake bleed screw location should be: 785C front: 103 kPa (14.9 psi) 789C front: 106 kPa (15.3 psi)
785C rear: 59 kPa (8.6 psi) 789C rear: 65 kPa (9.5 psi)
Low residual pressure may indicate a failed slack adjuster. High residual pressure may also indicate a failed slack adjuster or warped brake discs. To check for warped brake discs, rotate the wheel to see if the pressure fluctuates. If the pressure fluctuates while rotating the wheel, the brake discs are probably warped and should be replaced. To check for brake cooling oil leakage, block the brake cooling ports and pressurize each brake assembly to a maximum of 138 kPa (20 psi). Close off the air supply source and observe the pressure trapped in the brake assembly for five minutes. The trapped pressure should not decrease.
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Text Reference
SERVICE / RETARDER BRAKE AIR SYSTEM SERVICE BRAKES ENGAGED
Front Brake Cooler Diverter Valve
Service Brake Valve
Service Relay Valve
Pressure Protection Valve
ARC Relay Valve
Brake Light and Service / Retarder Switch
Retarder Valve
ARC Valve
Retarder Switch
Brake Cylinders
191
This schematic shows the flow of air through the service/retarder brake air system when the retarder (manual and automatic) is RELEASED, and the service brakes are ENGAGED. Supply air pressure flows from the large service brake air tank to the relay valves and the service brake valve, manual retarder valve, and the ARC valve. The manual retarder valve and the ARC solenoids block the flow of air. The service brake valve allows air to flow to two double check valves that block the passages to the manual retarder and ARC valves. Air pressure from the service brake valve flows through the double check valves to the service brake relay valve and the front brake oil cooler diverter valve. The service brake relay valve opens and metered air flows from the large service brake air tank to the brake cylinders. The relay valves reduce the time required to engage and release the brakes. A pair of double check valves above the brake cylinders prevent the flow of service brake air to the ARC relay valve. Air from the service brake valve also flows to the brake light switch and the service/retarder brake switch. Depressing the service brake pedal turns ON the brake lights and changes the transmission shift points and anti-hunt timer.
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Text Reference
When the manual retarder lever is moved, air flows through three double check valves that block the passages to the service brake valve and the ARC valve. Air pressure from the manual retarder brake valve flows through the double check valves to the service brake relay valve and the front brake oil cooler diverter valve. Air from the manual retarder brake valve also flows to the retarder switch, the brake light switch, and the service/retarder brake switch. Engaging the manual retarder turns ON the retarder dash lamp, the brake lights, and changes the transmission shift points and anti-hunt timer. When the ARC is activated, air flows through two double check valves that block the passages to the service brake valve and the manual retarder brake valve. Air pressure from the ARC valve flows through the double check valves to the front brake oil cooler diverter valve. When the ARC brake system is ENGAGED, the ARC relay valve opens and metered air flows from the service brake tank, through a pressure protection valve and the double check valves, to the three brake cylinders. The pressure protection valve prevents a total loss of air pressure in the service brake air system if the ARC relay valve fails. The protection valve opens to send flow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreases below 310 kPa (45 psi). Air from the ARC valve also flows to the retarder switch, the brake light switch, and the service/retarder brake switch. Engaging the ARC turns ON the retarder dash lamp, the brake lights, and changes the transmission shift points and anti-hunt timer.
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789C BRAKE COOLING SYSTEM
Text Reference
Hoist Pump Hoist Screens
Front Brakes
Rear Brakes
Hoist Valve Front Brake Oil Cooler
Outlet Relief Valve Torque Converter Charging Filter
Inlet Relief Valve
Diverter Valve
Rear Brake Oil Coolers Parking Brake Release Valve
Converter Outlet Filter
Parking Brake Filter
192
This schematic shows the flow of oil through the 789C brake cooling system. Three pump sections provide oil for rear brake cooling: the two-sections of the hoist pump and the fourth section of the torque converter pump. Two pump sections provide oil for front brake cooling: the torque converter charging and the brake release sections of the torque converter pump. All the pumps pull oil from the hydraulic tank through suction screens. Oil flows from the hoist pump sections through two screens to the hoist valve. In the HOLD and FLOAT positions, oil from the pump flows through the hoist valve to the rear brake cooling system. Oil flows from the fourth section of the torque conv erter pump, joins with the oil from the hoist valve, and flows to the rear brake oil coolers. Oil from all three pump sections combines and flows through the screens and rear brake oil coolers located on the right side of the engine. The rear brake oil coolers are cooled by the engine jacket water cooling system. From the coolers, oil flows through the brakes and returns to the hydraulic tank.
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Text Reference
The pressure in the rear brake cooling system is controlled by the oil cooler relief valve located in the hoist valve. The relief valve setting is 790 kPa (115 psi). Oil flows from the torque converter charging pump through the torque converter charging filter, the torque converter, and the torque converter outlet screen to the front brake oil cooler diverter valve. Oil flows from the brake release pump through the brake release filter to the brake release valve. The brake release valve controls the oil pressure to release the parking brakes, lock up the torque converter and shift the directional spool in the hoist valve. These functions require minimal oil flow. Most of the oil from the brake release pump flows through the brake release valve and joins with the torque converter charging pump oil at the front brake oil cooler diverter valve. When the service or retarder brakes are ENGAGED, the front brake oil cooler diverter valve allows brake cooling oil to flow through the front brake oil cooler to the front brakes. When the brakes are RELEASED, the oil bypasses the cooler and flows directly to the brakes. The front brake oil cooler is cooled by the engine aftercooler cooling system. The aftercooler cooling system does not have temperature regulators (thermostats) in the circuit. Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example). The brake cooling system on the 785C truck is slightly different from the 789C truck. The 785C truck does not have a fourth section on the torque converter pump for rear brake cooling. The parking brake release pump sends oil to the rear brake cooling system, not to the front brake cooling system.
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Text Reference
193
Shown is the left rear brake housing on a 789C truck. Brake cooling oil pressure can be tested at the two taps (arrow) located in the brake cooling oil tubes. One tap is located on the brake cooling inlet tube and another tap is located on the brake cooling outlet tube. The pressure measured at the brake inlet tube (from the oil coolers) will always be higher than the pressure measured at the brake outlet tube. With the brake cooling oil temperature between 79 to 93°C (175 to 200°F), the pressure measured at the brake inlet tube should be above 14 kPa (2 psi) at LOW IDLE and below 172 kPa (25 psi) at HIGH IDLE. Four brake oil temperature sensors, one for each brake, are located in the brake oil cooling tubes. The brake oil temperature sensors provide input signals to the VIMS, which keeps the operator informed of the brake cooling oil temperature. The most common cause of high brake cooling oil temperature is operating a truck in a gear that is too high for the grade and not maintaining sufficient engine speed. Engine speed should be kept at approximately 1900 rpm during long downhill hauls. Also, make sure the pistons in the slack adjuster are not stuck and retaining too much pressure on the brakes (see Visuals No. 189 and 190).
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Text Reference
BRAKE ELECTRONIC CONTROL SYSTEM
INPUT COMPONENTS Parking Brake Filter
Engine ECM Transmission/chassis ECM
Brake Air Pressure
VIMS
Left Brake Release Pressure Right Brake Release Pressure Differential Filter
Throttle Sensor
Transmission Output Speed Sensor
Actual Gear Switch
Engine Speed/timing Sensor
Service/retarder Brake Switch
OUTPUT COMPONENTS
Differential Pressure Differential Oil Level
ARC On Input
Off Input
TCS
Shift Lever Switch
Parking / Secondary Brake Switch
Differential Oil Temp Sensor
Arc On / Off Switch
CAT DATA LINK
Service Tool
Brake Overstroke Switch
Differential Fan Relay
ARC Supply Solenoid
Engine Output Speed Sensor
ARC
ARC Control Solenoid
Retarder Pressure Switch
Retarder Engaged Lamp
Auto Retarder Pressure Switch
TCS Engaged Lamp
TCS Test Switch
TCS TCS Selector Solenoid Left and Right
Left Wheel Speed Sensor Proportional (Servo) Solenoid
Right Wheel Speed Sensor
194
BRAKE ELECTRONIC CONTROL SYSTEM
The "C" Series trucks use an additional Electronic Control Module (ECM) for controlling both the Automatic Retarder Control (ARC) and the Traction Control System (TCS). The Automatic Retarder Control (ARC) and the Traction Control System (TCS) control modules are replaced with one Brake ECM. The Brake ECM controls both the ARC and the TCS functions. The TCS is now on the CAT Data Link, and the Electronic Technician (ET) service tool can be used to diagnose the TCS. The Brake ECM receives information from various input components such as the Engine Output Speed (EOS) sensor, retarder pressure switch, left and right wheel speed sensors, and the TCS test switch. Based on the input information, the Brake ECM determines whether the service/retarder brakes should ENGAGE for the ARC or the parking/secondary brakes should ENGAGE for the TCS. These actions are accomplished by sending signals to various output components.
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Text Reference
Output components include the ARC supply and control solenoids, the retarder ENGAGED lamp, the TCS selector and proportional solenoids, and the TCS ENGAGED lamp. The Brake ECM also provides the service technician with enhanced diagnostic capabilities through the use of onboard memory, which stores possible diagnostic codes for retrieval at the time of service. The Engine ECM, the Transmission/Chassis ECM, the Vital Information Management System (VIMS), and the Brake ECM all communicate through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared. The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used to perform several diagnostic and programming functions. Some of the diagnostic and programming functions that the service tools can pe rform are: - Display real time status of input and output parameters - Display the internal clock hour reading - Display the number of occurrences and the hour reading of the first and last occurrence for each logged diagnostic code and event - Display the definition for each logged diagnostic code and event - Display the supply and control solenoid engagement counter - Program the ARC control speed - Perform ARC diagnostic tests - Upload new Flash files
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Text Reference
195
The Brake ECM (arrow) is located in the compartment at the rear of the cab. The Brake ECM does not have a diagnostic window like the ARC and the TCS used on the "B" Series trucks. All diagnostic and programming functions must be performed with an Electronic Control Analyzer Programmer (ECAP) or a laptop computer with the Electronic Technician (ET) software installed. ET is the tool of choice because the Brake ECM can be reprogrammed with a "flash" file using the WinFlash application of ET. ECAP cannot upload "flash" files. The Brake ECM looks like the Engine ECM with two 40-pin connectors, but the Brake ECM does not have fittings for cooling fluid. Also, the Brake ECM has no access plate for a personality module.
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Text Reference
AUTOMATIC RETARDER CONTROL Engine Speed Sensor
Brake ECM (ARC / TCS) On Input
Arc On / Off Switch Off Input Service Tool Engine ECM
CAT Data Link
Transmission / Chassis ECM VIMS
Retarder Engaged Lamp
Air From Service Brake Reservoir
Supply Solenoid Vent
Vent Control Solenoid
Service Brake Valve
To Service / Retarder Brake Relay Valve
Manual Retarder Valve
Automatic Retarder Valve Auto Retarder Pressure Switch
Retarder Pressure Switch
To ARC Relay Valve
196
Automatic Retarder Control (ARC)
The Automatic Retarder Control (ARC) system function is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed. The ARC system engages the service/retarder brakes. If the ON/OFF switch is moved to the ON position, the ARC will be activated if the throttle pedal is not depressed and the parking/ secondary brakes are RELEASED. The ARC system is disabled when the throttle is depressed or when the parking/secondary brakes are ENGAGED. The ARC is not connected to the service brakes and the manual retarder. When the ARC is ENGAGED, air flows from the ARC valve to a separate relay valve located near the brake master cylinders (see Visual No. 182). The ARC is set at the factory to maintain a constant engine speed of 1900 ± 50 rpm (engine speed setting is programmable). When the ARC initially takes control of retarding, the engine speed may oscillate out of the ± 50 rpm target, but the engine speed should stabilize within a few seconds.
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Text Reference
For proper operation of the ARC, the operator needs only to activate the control with the ARC ON/OFF switch and select the correct gear for the grade, load, and ground conditions. The ARC is designed to allow the transmission to upshift to the gear selected by the shift lever. After the transmission shifts to the gear selected by the ope rator and the engine speed exceeds 1900 rpm, the ARC will apply the retarder as needed to maintain a constant engine speed. The ARC system also provides engine overspeed protection. If an unsafe engine speed is reached, the ARC will engage the brakes, even if the ARC ON/OFF switch is in the OFF position and the throttle is depressed. Trucks approaching an overspeed condition will sound a horn and activate a light at 2100 rpm. If the operator ignores the light and horn, the ARC will engage the retarder at 2180 rpm. If the engine speed continues to increase, the Transmission/Chassis ECM will either upshift (one gear only above shift lever position) or unlock the torque converter (if the shift lever is in the top gear position) at 2300 rpm. The ARC also provides service personnel with enhanced diagnostic capabilities through the use of onboard memory, which stores possible faults, solenoid cycle counts and other service information for retrieval at the time of service. By using an ECAP or a laptop computer with the Electronic Technician (ET) software installed, service personnel can access the stored diagnostic information or set the adjustable engine speed control setting. The Auto Retarder Control receives signals from several switches and sensors. The control analyzes the various input signals and sends signals to the output components. The output components are two solenoids and a lamp. NOTE: The ARC ON/OFF switch must be in the OFF position to run the ARC diagnostic test with ET. INSTRUCTOR NOTE: For more detailed information about the Automatic Retarder Control (ARC) system, refer to the Service Manual Module "Off-Highway Truck/Tractors Brake Electronic Control System" (Form SENR1503).
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Text Reference
1
2
197
Shown is the location of the Engine Output Speed (EOS) sensor (1) that provides the primary input signal used by the ARC. The engine speed information is the main parameter that the Brake ECM uses to control retarding. The engine speed sensor is a frequency sensor that generates an AC signal from the passing flywheel gear teeth. The EOS sensor also provides an input signal to the Transmission/Chassis ECM for Transmission Output Speed (TOS) ratification and lockup clutch shift time. The Transmission/Chassis ECM uses the EOS signal and the Converter Output Speed (COS) signal to calculate torque converter lockup clutch shift time. This information is then sent to VIMS. The EOS signal is also used for TOS ratification. EOS is compared to the EOS calculated from the TOS and the ratio for the current transmission gear. If the speeds do not agree, the transmission will not downshift. If EOS is less than 1000 rpm the lockup clutch will release. If EOS exceeds 2300 rpm the lockup clutch will release. If EOS exceeds 2500 rpm the transmission will upshift as many gears as necessary to keep engine speed less than 2500 rpm. The engine speed/timing sensor (2) is also used by the ARC for diagnostic purposes. If the Brake ECM receives an input signal from the engine speed/timing sensor, but not the EOS sensor, the Brake ECM will log an engine speed fault. The ARC will not function without an engine speed signal from EOS sensor (1).
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Text Reference
NOTE: The 8T5200 Signal Generator/Counter Group can be connected to the engine speed sensor wiring harness and be used to simulate engine speed for diagnostic purposes. A 196-1900 adapter is required to increase the frequency potential from the signal generator when connecting to the ECM's used on these trucks. To connect the 8T5201 Signal Generator to the engine speed sensor wiring harness, fabricate jumper wires and connect the 8T5198 Adapter Cable (part of the 8T5200 Signal Generator/Counter Group) to the speed sensor harness Deutsch DT connector. 8T5198 Adapter
Deutsch DT Connector
Pin B
J765 BU Pin 2 (ground)
Pin C
450 YL Pin 1 (signal)
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Text Reference
4 3 2 5
1
198
Shown is the location of the retarder pressure switch (1). The retarder pressure switch signals the Brake ECM when manual or automatic retarder air pressure is present. The switch is normally open and closes when the manual or automatic retarder is engaged. A fault is recorded when the Brake ECM detects the absence of retarder pressure (switch open) while the supply solenoid and the control solenoid are energized. The auto retarder pressure switch (2) signals the Brake ECM when air pressure is present and the automatic retarder valve (3) is functioning. The auto retarder pressure switch is located in front of the cab in the output port of the automatic retarder valve. The switch is normally closed and opens only when the auto retarder is engaged. A fault is recorded when the Brake ECM detects the presence of auto retarder pressure (switch open) while the supply solenoid and the control solenoid are not energized. The supply solenoid valve (4) turns ON or OFF to control the flow of supply air to the automatic retarder valve (3). The Brake ECM energizes the supply solenoid valve with +Battery voltage (24 Volts) at 100 rpm less than the programmed control speed setting. Normally, the reduced speed will be 1800 rpm, since the control speed is set to 1900 rpm at the factory. A fault is recorded if the Brake ECM senses the signal to the supply solenoid as open, shorted to ground, or shorted to battery.
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Text Reference
The control solenoid valve (5) modulates the air flow to the brakes during automatic retarding. The control solenoid receives a Pulse Width Modulated (PWM) signal from the Brake ECM. The longer the duty cycle, the more time the control solenoid valve is open, and more air pressure is allowed to the brakes. Voltage to the control solenoid increases proportionally from zero to approximately 22 Volts with the demand for more brake pressure. A fault is recorded if the Brake ECM senses the signal to the control solenoid as open, shorted to ground, or shorted to battery. Normal resistance through the supply and control solenoids is 31 Ohms. An excess resistance of approximately 40 Ohms will prevent the valves from opening and will cause a supply or control valve fault to be logged. Therefore, a measurement of approximately 71 Ohms or more will show that the solenoid is defective. The Brake ECM can also determine if the solenoid valves have malfunctioned (valves leaking). If air pressure is present at the auto retarder pressure switch when the solenoids are DEENERGIZED, the auto retarder pressure switch will signal the Brake ECM that the ARC valve has malfunctioned.
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Text Reference
199
Hydraulic Automatic Retarder Control (ARC)
Signal air from the primary air tank flows to the service brake valve and the retarder valve. A shuttle valve, after these valves, then sends the highest signal pressure to the service brake relay valve. The service brake relay valve opens and actuates the brake cylinders with a greater volume of air from the primary air tank. An addition to the air system is the front brake cooling oil diverter solenoid. Air is supplied to this valve from a smaller secondary air tank behind the cab. The Brake ECM energizes this valve when the service brakes are applied. When the Brake ECM energizes this solenoid, signal air is sent to the diverter valve for the front brake cooling oil. Brake cooling oil is then sent through the cooler for front brake cooling oil.
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Text Reference
200
This schematic shows the flow of oil for the ARC system when ENABLED. The parking brake release pump provides oil flow for the ARC system. The flow continues from the pump, through a check valve to the ARC valve. The ARC valve modulates the amount of pressure to the service brakes in order to control the ground speed of the truck. The air over hydraulic brake cylinders also use the same service brakes. A shuttle valve between the ARC system and brake cylinders separates these two systems. Whichever system has the greatest pressure, that system will control the service brakes.
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Text Reference
201
The hydraulic ARC valve (arrow) is located on the left frame rail near the rear differential. This valve contains a supply solenoid valve and a control solenoid valve. A purge solenoid valve is located on the bottom of the ARC valve. The ARC accumulator is located to the right of the ARC valve. NOTE: The hydraulic ARC valve performs the same functions as the previous air controlled ARC valve. The hydraulic ARC valve use oil pressure instead of air pressure.
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ENGINE ON / ARC OFF Control Solenoid Valve Spool To Tank
Supply Solenoid Valve
Accumulator
Check Valve Pump Purge Solenoid Valve
To Service Brakes
202
Supply oil from the parking brake release pump flows across a check valve. Oil flow then enters the ARC valve. Hydraulic flow is stopped because the ARC spool is in the blocked position. Hydraulic flow is then directed to the accumulator to charge the accumulator to the same pressure as the parking brake release system pressure. Hydraulic flow is also routed through the supply solenoid valve to apply pilot pressure to the left end of the ARC spool. This pressure will keep the ARC spool in the blocked position.
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Text Reference
ENGINE ON / ARC ON Control Solenoid Valve
ON Spool
To Tank
Supply Solenoid Valve
Accumulator
ON
Check Valve Pump Purge Solenoid Valve
To Service Brakes
203
The Brake ECM supplies current to the supply solenoid. The supply solenoid valve sends pilot oil to the right end of the ARC spool. This pilot oil shifts the ARC spool to the left opening the left side of the ARC spool to tank. At the same time, pump supply oil is directed to the right side of the ARC spool. Now, pump oil is directed to the control solenoid valve. The Brake ECM will send varying levels of current to the control solenoid. This variable current will modulate the spool within the proportional valve. The level of current is dependent on the brake requirements for the ARC valve to maintain a constant breaking force. When the control solenoid is energized, the pin moves to the right and pushes against the ball. The ball blocks the pump supply oil from flowing to the drain. Pressure increases in the chamber to the left of the spool to move the spool to the right. When the spool moves to the right, pump supply oil flows to the service brakes. In order to maintain the correct brake pressure, the Brake ECM will vary the current to the control solenoid to open and close the oil drain port.
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Text Reference
ENGINE OFF / ARC OFF Control Solenoid Valve Spool To Tank
Supply Solenoid Valve
Accumulator
Check Valve Pump Purge Solenoid Valve
ON
To Service Brakes
204
No current is supplied from the Brake ECM to the supply solenoid. The supply solenoid valve directs any pressurized oil acting on the ARC spool to flow to the tank. Current is supplied from the Steering Bleed Control to the purge solenoid valve for approximately 70 seconds. This allows the pressure within the accumulator to drain from the accumulator back to the tank.
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Text Reference
AUTOMATIC RETARDER CONTROL ARC ENGAGED
Engine Speed Sensor On Input ARC On / Off Switch
Brake ECM (ARC / TCS)
Off Input
Service Tool Connector
Retarder Engaged Lamp
CAT Data Link
Front Brake Cooling Diverter Solenoid Parking Brake Release Pump Service Brakes Steering Bleed Control
ARC Spool Supply Solenoid
Purge Solenoid
To Tank
Control Solenoid
ARC Valve
205
The introduction of the hydraulic ARC control valve has required a number of additional component changes. The basic function of the new system remains the same as the previous system. The Engine ECM, the Transmission/Chassis ECM, the Vital Information Management System (VIMS), and the Brake ECM all communicate through the CAT DATA Link. Communication between the electronic controls allows the sensors of each system to be shared.
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Text Reference
206
The steering bleed down control (1) is located in the compartment behind the cab. While the steering bleed control is not a new component, the control serves an additional function. The steering bleed control is used to purge the ARC accumulator when the machine is shut down. When the control receives a signal from the key start switch, a timer built into the control will energize the purge solenoid for a period of approximately 70 seconds to purge the ARC accumulator.
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Text Reference
207
One of the new components, located in the compartment behind the cab, is the front brake cooling diverter solenoid (arrow). When the ARC is engaged, the Brake ECM energizes this solenoid to send an air signal to shift the brake cooling oil diverter valve. This will route the brake cooling oil through the front brake oil cooler for increased cooling. Normally the brake cooling oil is routed around the front brake oil cooler. This is a 24 V normally closed solenoid valve.
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Text Reference
208
Shown is the location of the Engine Output Speed (EOS) sensor that provides the primary input signal used by the ARC. The EOS sensor is a passive (two wire) sensor and is located on top of the flywheel housing. The engine speed information is the main parameter that the Brake ECM uses to control retarding. The engine speed sensor is a frequency sensor that generates an AC signal from the passing flywheel gear teeth. The EOS sensor also provides an input signal to the Transmission/Chassis ECM for Transmission Output Speed (TOS) ratification and lockup clutch shift time. The Transmission/Chassis ECM uses the EOS signal and the Converter Output Speed (COS) signal to calculate torque converter lockup clutch shift time. This information is then sent to VIMS. The EOS signal is also used for TOS ratification. EOS is compared to the EOS calculated from the TOS and the ratio for the current transmission gear. If the speeds do not agree, the transmission will not downshift. If EOS is less than 1000 rpm the lockup clutch will release. If EOS exceeds 2300 rpm the lockup clutch will release. If EOS exceeds 2500 rpm the transmission will upshift as many gears as necessary to keep engine speed less than 2500 rpm. ARC also uses the engine speed/timing sensor for diagnostic purposes. The engine/timing speed sensor is located near the rear of the left camshaft. If the Brake ECM receives an input signal from the engine speed/timing sensor, but not the EOS sensor, the Brake ECM will log a n engine speed fault. The ARC will not function without an engine speed signal from EOS sensor.
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Text Reference
TRACTION CONTROL SYSTEM Brake ECM (ARC / TCS)
Electronic Service Tool
TCS Engaged Lamp
Service / Retarder Brake Switch Transmission Output Speed Sensor
TCS Selector Solenoid Left and Right
CAT Data Link
TCS Test Switch
Proportional Solenoid
Left Wheel Speed Sensor Right Wheel Speed Sensor
+ 10V to Wheel Sensors
209
Traction Control System (TCS)
The Traction Control System (TCS) uses the rear parking/secondary brakes (spring engage d and hydraulically released) to decrease the revolutions of a spinning wheel. The TCS allows the tire with better underfoot conditions to receive an increased amount of torque. The system is controlled by the Brake ECM (see Visuals No. 194 and 195). The Brake ECM monitors the drive wheels through three input signals: one at each drive axle, and one at the transmission output shaft. When a spinning drive wheel is detected, the Brake ECM sends a signal to the selector and proportional valves which ENGAGE the brake of the affected wheel. When the condition has improved and the ratio between the right and left axles returns to 1:1, the Brake ECM sends a signal to RELEASE the brake. The TCS was formerly referred to as the Automatic Electronic Traction Aid (AETA). The operation of the system has not changed. The main differences are the appearance of the ECM, and the TCS is now on the CAT Data Link. Also, the ECAP and ET Service Tools can communicate with the TCS.
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A service/retarder brake switch (see Visual No. 128) provides an input signal to the TCS through the CAT Data Link and performs two functions: 1. When the service brakes or retarder are ENGAGED, the TCS function is stopped. 2. The service/retarder brake switch provides the input signal needed to perform a diagnostic test. When the TCS test switch and the retarder lever are ENGAGED simultaneously, the TCS will engage each rear brake independently. Install two pressure gauges on the TCS valve, and observe the pressure readings during the test cycle. The left brake pressure will decrease and increase. After a short pause, the right brake pressure will decrease and increase. The test will repeat as long as the TCS test switch and the retarder lever are ENGAGED. The TCS valve has a left and right brake release pressure sensor. A laptop computer with the ET software installed can also be used to view the left and right parking brake pressures during the test discussed above in function No. 2. When the proportional solenoid is ENERGIZED, ET will show 44% when the brake is FULLY ENGAGED. NOTE: During the diagnostic test, the parking/secondary brakes must be released. INSTRUCTOR NOTE: For more detailed information about the Traction Control System (TCS), refer to the Service Manual Module "Off-Highway Truck/Tractors Brake Electronic Control System" (Form SENR1503).
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210
Shown is the right rear wheel speed sensor (arrow). The TCS monitors the drive wheels through three input speed signals: one at each drive axle, and one at the transmission output shaft. The Transmission Output Speed (TOS) sensor (see Visual No. 127) monitors the ground speed of the machine and provides input signals to the TCS through the CAT Data Link. The TCS uses the TOS sensor to disable the TCS when ground speed is above 19.3 km/h (12 mph).
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4
Text Reference
4
3
3
2
1
211
The Traction Control System (TCS) valve is mounted inside the rear of the left frame rail. Two solenoids are mounted on the valve. Electrical signals from the Brake ECM cause the selector solenoid valve (1) to shift and select either the left or right parking brake. If the selector valve shifts to the left parking brake hydraulic circuit, the control oil is drained. The left reducing spool of the control valve can then shift and engage the parking brake. The Brake ECM energizes the selector solenoid valve with + Battery voltage (24 Volts). Normal resistance through the selector solenoid is between 18 and 45 Ohms. The proportional solenoid valve (2) controls the volume of oil being drained from the selected parking brake control circuit. The rate of flow is controlled by a signal from the Brake ECM. The proportional solenoid receives a current between 100 and 680 mA (or 0 to 12 Volts) from the Brake ECM. The more current that is sent, the more the proportional solenoid valve is open, and more oil pressure is drained from the brakes. Normal resistance through the solenoid is between 12 and 22 Ohms. The pressure taps (3) or pressure sensors (4) can be used to check the left and right brake release pressures when performing diagnostic tests on the TCS. The pressure at the taps in the TCS valve will be slightly less than the brake release pressure measured at the wheels. The pressure sensors are also used to provide parking brake dragging information to the operator.
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Text Reference
TRACTION CONTROL SYSTEM (TCS) ENGINE RUNNING/BRAKES RELEASED Test Switch Service / Retarder Brake Switch
Left Drive Axle Input Signals
Ball Check Transmission Speed Sensor
Output Signals
Orifice
Tcs Engaged Lamp
Screen Selector Solenoid
Right Drive Axle
Parking Brake Valve
Proportional Solenoid
212
Shown is the TCS with the engine running and the brakes RELEASED. When the machine is started: - Oil flows from parking brake release pump through the brake release oil filter where the flow is divided. One line from the filter directs oil to the parking brake release valve. The other line sends oil to the signal port (right end of signal piston) of the TCS control valve. - Oil flow to the TCS control valve signal port causes the ball check piston to move to the left and unseat the drain ball check valve. Opening the drain ball check valve opens a drain passage to the hydraulic tank.
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When the operator releases the parking brakes: - Air pressure is increased at the parking brake release valve forcing the valve spool down. - Parking brake release oil can now flow through the parking brake release valve to the TCS control valve. - In the control valve, oil closes the parking/secondary ball check valve and flows through the screen. - Oil flows through the right and left brake control circuit orifices. - Oil flows to the ends of the left and right brake reducing valve spools. - When the control circuit pressure is high enough, the reducing spools shift toward the center of the TCS control valve and parking brake release oil flows to release the brakes.
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Text Reference
TRACTION CONTROL SYSTEM (TCS) ENGINE RUNNING/LEFT BRAKE ENGAGED Test Switch Service / Retarder Brake Switch
Left Drive Axle Input Signals
Ball Check Transmission Speed Sensor Orifice
Tcs Engaged Lamp
Screen Selector Solenoid
Right Drive Axle
Output Signals
Parking Brake Valve
Proportional Solenoid
213
Shown is the TCS with the engine running and the left brake ENGAGED. When signals from the sensors indicate that the left wheel is spinning 60% faster than the right wheel, the following sequence of events occurs: - The Brake ECM sends a signal to the selector solenoid valve and the proportional solenoid valve. - The selector solenoid valve opens a passage between the outer end of the left brake pressure reducing valve and the proportional solenoid valve. - The proportional solenoid valve opens a passage from the selector solenoid valve to drain. The proportional solenoid valve also controls the rate at which the oil is allowed to drain. - Control circuit oil drains through the selector valve and enters the proportional valve. The reducing valve spool for the left parking brake shifts and blocks the flow of oil to the parking brake. - Oil in the left parking brake control circuit begins to drain. - The left parking brake begins to ENGAGE. - The left brake orifice restricts the flow of oil from the parking brake release valve.
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Text Reference
When the signals from the sensors indicate that the left wheel is no longer spinning, the following sequence occurs: - The Brake ECM stops sending signals to the selector solenoid and the proportional solenoid. - The selector solenoid valve and proportional solenoid valve block the passage to drain and allow the control circuit pressure to increase. - The left brake reducing valve spool shifts to the center position and blocks the passage to drain. - Parking brake release oil is directed to the left parking brake and the brake is RELEASED.
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Text Reference
3
2
1
214
OPTIONAL EQUIPMENT Flexxaire TM Fan
Shown is a 3516B Engine with a FlexxaireTM Fan installed. The FlexxaireTM fan provides full control of air movement through the radiator with an automatically controlled, variable pitch fan. The fan is designed to help control cooling requirements in specific applications such as cold weather and high altitude. The thermostatic controller automatically adjusts the blade pitch to maintain an optimum engine coolant temperature. With zero-pitch start-up, the air dam effect prevents air flow through the radiator and the e ngine reaches the recommended operating temperature more quickly. The pitch will vary throughout the day based on the engine cooling temperature and air conditioning requirements. The automatic blade pitch control reduces the horsepower loss when engine cooling is not required. The 10 fan blades attach to the hub assembly (1). A coolant temperature sensor (2) and an air conditioning pressure sensor (see Visual No. 62) provide input signals to an electronic control box located behind the cab (see next page). The electronic control analyzes the input signals and sends an electrical signal to the actuator (3). The actuator rotates and changes the fan pitch as needed to increase or decrease the engine coolant temperature.
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Text Reference
1
3
4
2
215
The FlexxaireTM Fan electronic control box (1) and the remote display (2) are located in the compartment behind the operator's station. The control box is used to set up and calibrate the Flexxaire™ fan. Remove the cover from the control box and follow the instructions on the label inside the cover. The FlexxaireTM control box provides many features. The customer must decide which features he wants to use before setting up the system. Some of the features are: Timed Auto-Purge, Purge Interval Override, Temperature Driven Auto-Purge: Off-highway Trucks normally PULL air through the radiator. For a PURGE to occur, the fan blades rotate and PUSH air through the radiator. Changing air flow direction can help clear debris from the radiator. Actuator Stall Detection: If the fan pitch actuator encounters excessive resistance (bolt falls into the linkage), the control will sense the increased current and attempt an automatic calibration. If the obstruction continues, as a safety measure, the control will rotate the fan blades to full pitch. Second Fluid Temperature Control: A second temperature sensor can be installed to control the fan pitch in addition to the engine coolant temperature sensor (brake oil temperature).
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Blaze Blocker: A fire suppression system can provide an input signal to the control that will rotate the fan blades to the NEUTRAL position. In the NEUTRAL position, the fan provides no air flow. Limiting the air flow reduces the amount of oxygen to the fire, and the fire suppressant is not blown from the engine compartment.
The following two FlexxaireTM Fan Controls must be set up properly: Actuator Limits: This procedure sets the travel limits and the NEUTRAL p osition of the actuator. Temperature Set Point Calibration: This procedure sets the temperature range that the controller will try to maintain by changing the fan pitch.
The remote display (2) can be used to change the air flow from PUSH to PULL by depressing the air flow button (3). The nine LED bar display to the right of the air flow button indicates the position of the fan. The bottom four LED's indicate the PULL direction. The center LED indicates the NEUTRAL position. The top four LED's indicate the PUSH direction. The purge button (4) will start the purge cycle if one has been programmed into the control (optional). INSTRUCTOR NOTE: More detailed information about the Flexxaire TM Fan System can be found in the Service Manual module "Flexxaire TM Fan Installation And Maintenance Manual" (Form SEBC1152).
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216
CONCLUSION
This presentation has provided a basic introduction to the Caterpillar 785C and 789C Offhighway Trucks. All the major component locations were identified and the major systems were discussed. When used in conjunction with the service manual, the information in this package should permit the serviceman to analyze problems in any of the major systems on these trucks.
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VISUAL LIST 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42.
789C model view Right side 789C truck Front of 789C truck Truck body options Walk around inspection Maintenance checks Front wheel bearing Front suspension cylinder Air filter housing Right side engine Transmission charging filter Transmission hydraulic tank Final drive Differential oil level Safety cable Fuel tank Primary fuel filter Parking brake and torque converter Brake cylinder breathers Front air dryer 789C engine oil filters 785C engine oil filters Oil change connector Secondary fuel filters Engine shutdown switch Air filter restriction indicators 789C cooling system Air cleaner indicators Ether cylinders Batteries Lubrication tank Steering system tank Air tank drain valve Windshield washer reservoir Daily checks Operator's station Operator and trainer seats Hoist control lever Dash (left side) Operator controls Switches and signals Manual retarder lever
43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78 79. 80. 81. 82. 83.
Brake and throttle pedals Shift console Overhead switches Circuit breaker panel Center dash panel Rocker switches VIMS message center module VIMS interface modules VIMS main module VIMS diagnostic connector Electronic Technician (ET) 3516B engine model view Electronic control system component diagram Engine ECM Atmospheric pressure sensor Engine speed/timing sensor Throttle position sensor EUI fuel injector solenoid Input switches and sensors Air conditioner compressor switch Crankcase pressure sensor ECM logged events Additional ECM logged events Systems controlled by ECM Engine oil pre-lubrication Speed fan control Oil renewal system components Oil level switches Cooling system Radiator Water pump Coolant Engine (right side) Jacket water coolant flow Auxiliary (aftercooler) water pump Rear aftercooler temperature sensor 789C air charging system Lubrication system Oil filters 785C engine oil filters Engine oil system
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VISUAL LIST 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104.
Primary fuel filter Fuel transfer pump Secondary fuel filters Fuel injectors Fuel system circuit Air induction and exhaust system Turbocharger inlet pressure sensor 351B turbochargers Exhaust temperature sensor 3512B air induction and exhaust system Power train components Torque converter Torque converter (converter drive) Torque converter drive (direct drive) Torque converter pump (four sections) Torque converter charging filter Torque converter inlet relief valve Torque converter outlet screen Brake oil cooler and diverter valve Parking brake release valve Torque converter lockup clutch valve (iron) 105. Torque converter lockup clutch control (direct drive) 106. Torque converter hydraulic system 107. Transfer gears 108. Transmission lube supply hose 109. Power shift planetary transmission 110. Transmission pump 111. Transmission scavenge screens 112. Transmission charging filter 113. Transmission oil cooler bypass valve and oil cooler 114. Transmission charging pump 115. Transmission clutch pressures 116. ICM transmission controls (sectional view) 117. Transmission hydraulic system 118. Rear axle pump 119. Pump supply hose 120. Oil filter bypass switch
121. Rear axle oil cooling and filter system 122. Double reduction planetary gear final drives 123. Transmission/Chassis ECM 124. Transmission/Chassis electronic control system 125. Shift lever switch 126. Transmission gear switch 127. Transmission Output Speed (TOS) sensor 128. Service/retarder brake switch 129. Body position sensor 130. Steering system 131. 789C steering system (no steer/maximum flow 132 785C steering system (hold) 133. Steering tank and filter 134. 785C steering pump 135. 785C steering pump (maximum flow) 136. Pump compensator valve 137. 785C steering pump (minimum flow) 138. 789C steering pump 139. 789C steering pump supply oil 140. 789C steering pump operation (maximum flow) 141. 789C steering pump (low pressure standby) 142. Accumulator charging valve 143. Load sensing controller 144. 789C solenoid and relief valve manifold 145. 785C solenoid and relief valve manifold 146. Solenoid and relief valve manifold (sectional view) 147. 789C steering directional valve 148. Steering directional valve (no turn) 149. Steering directional valve (right turn) 150. 785C solenoid and relief valve manifold and crossover relief valves 151. 785C crossover relief system (external impact) 152. 789C Hand Metering Unit (HMU) 153. 789C steering accumulators
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VISUAL LIST 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165. 166.
Shutdown control Hoist control system Hoist lever Hoist control position sensor Hoist, converter and brake tank Hydraulic tanks (rear) Two-section hoist pump Hoist screens Pump supply ports Counterbalance valve Hoist control valve (hold) Hoist control valve (raise) Hoist counterbalance valve (raise, lower and float) 167. "C" Series hoist control valve (lower) 168. "C" Series hoist control valve (float) 169. Two-stage hoist cylinders 170. Hoist system (hold) 171. Air and brake systems 172. Oil cooled brake assembly (cutaway) 173. Air charging system 174. 789C air dryers 175. Service/retarder brake tank 176. Pressure protection valve 177. Automatic lubrication solenoid air valve 178. Parking/secondary brake tank 179. 789C air charging system 180. Manual retarder valve 181. Service brake valve 182. Inverter valve signal port 183. Brake release valve 184. Normal parking and secondary brake operation 185. Parking/secondary brakes released and parking brakes engaged 186. Service brake and manual retarder relay valve 187. Brake oil makeup tank 188. Brake cylinder (engaged) 189. Slack adjuster (iron) 190. Slack adjuster (released and engaged)
191. Service/retarder brake air system (engaged) 192. 789C brake oil cooling schematic 193. Brake cooling oil pressure tap 194. Brake electronic control system 195. Brake ECM (iron) 196. Automatic Retarder Control (ARC) schematic 197. Engine Output Speed (EOS) sensor 198. Retarder pressure switch 199. Service/retarder brake air system 200. Hydraulic ARC System 201. Hydraulic ARC Valve 202. Engine On/ARC Off 203. Engine On/ARC On 204. Engine Off/ARC Off 205. Automatic retarder control schematic (engaged) 206. Steering bleed down control 207. Brake cooling diverter solenoid 208. Engine Output Speed (EOS) sensor 209. Traction Control System (TCS) schematic 210. Wheel speed sensor 211. Traction Control System (TCS) valve 212. Traction Control System (TCS) operation (brakes released) 213. Traction Control System (TCS) operation (left brake engaged) 214. Flexxaire™ fan 215. Flexxaire™ fan electronic control box 216. Model rear view
