HOIST RELIEF HOIST CONTROL VALVE VALVE OIL COOLING RELIEF VALVE
HOIST PUMP
HOIST RELIEF VALVE
Page:
VI-1
ORIFICE PLATE OIL COOLING HOIST CONTROL RELIEF VALVE VALVE
777D Off Highway Truck CHAPTER : HOIST SYSTEM
TWO STAGE HOIST CYLINDER RAISE
FIRST STAGE
SECOND STAGE
Page:
VI-2
777D Off Highway Truck CHAPTER : HOIST SYSTEM
TWO STAGE HOIST CYLINDER LOWER
Page:
VI-3
777D Off Highway Truck CHAPTER : HOIST SYSTEM
HOIST VALVE RELIEF VALVE
HOLD FROM PUMP
LOAD CHECK VALVE
DETENT
TO BRAKE COOLERS
RELIEF VALVE
CYLINDER ROD END PORT
CYLINDER HEAD END PORT
HOIST VALVE RAISE FROM PUMP
LOAD CHECK VALVE
DETENT
TO BRAKE COOLERS
Page:
VI-4
CYLINDER ROD END PORT
CYLINDER HEAD END PORT
Page: VI-5
HOIST SYSTEM HOLD LOAD CHECK VALVE HOIST RELIEF VALVE
HOIST PUMP
777D Off Highway Truck
TO HOIST & BRAKE COOLER
CHAPTER : HOIST SYSTEM
BRAKE COOLING RELIEF VALVE
777D Off Highway Truck CHAPTER : HOIST SYSTEM
HOIST VALVE LOWER RELIEF VALVE FROM PUMP
LOAD CHECK
DETENT
NO FLOW FROM CYLINDERS HEAD END
TO CYLINDERS ROD END
RELIEF VALVE
HOIST VALVE FLOAT FROM PUMP
LOAD CHECK
DETENT
Page:
VI-6
Page: VI-7
HOIST SYSTEM RAISE
LOAD CHECK VALVE HOIST RELIEF VALVE
BRAKE COOLING RELIEF VALVE
777D Off Highway Truck
CHAPTER : HOIST SYSTEM
TO DIVERTER VALVE & HOIST/BRAKE COOLER
777D Off Highway Truck CHAPTER : HOIST SYSTEM
LAB EXERCISES Lab A Worksheet Hoist System Component Reference Checklist Directions: Place the correct letter next to the component and give a brief description of each. Example: _____ Hoist Pump(s) Supplies oil flow to the hoist system. The 769D - 777D only have one pump. Hoist System Components
_____ Hoist Pump
_____ Hoist Control Valve
_____ Hoist Relief Valve
_____ Hoist Diverter Valve
_____ Parking Brake Release Valve
_____ Oil Cooling System Relief Valve
_____ Hoist Lever Switch (Transmission Neutralizer)
_____ Orifice Plate (769D - 777D)
Page:
VI-8
777D Off Highway Truck CHAPTER : HOIST SYSTEM
LAB EXERCISES Lab B: Adjust Hoist Lever Linkage BACKGROUND INFORMATION
This lab allows you to gain hands on experience checking and adjusting the hoist control lever linkage adjustment. The lab also allows you to gain hands on experience checking the transmission neutralizer switch for correct operation.
MATERIALS NEEDED
Mechanic’s Tool Box and hand tools Appropriate Service Manual Modules: Hydraulic System Operation, Testing and Adjusting
GROUP EXERCISE
Check and adjust the hoist control lever linkage on an Off-highway Truck. After the linkage has been checked and adjusted, check for correct operation of the transmission neutralizer switch.
Page:
VI-9
777D Off Highway Truck CHAPTER : HOIST SYSTEM
LAB EXERCISES Lab C: Hoist System Diagnostic Testing BACKGROUND INFORMATION
This lab allows you to gain hands on experience performing pressure relief, cycle time and drift tests.
MATERIALS NEEDED
Appropriate Service Manual Module Mechanic’s Tool Box and hand tools 1 - 8T0857 Gauge (0-1450 psi) 1 - 8T0859 Gauge (0-3600 psi) 2 - 6V3989 Nipple 2 - 6V4143 Valved Coupler 2 - 6V3079 Diagnostic Hose 2 - 6J3958 1/8-27 NPTF Union 1 - 8T8902 11/16-16 ORFS Tee 1 - Stopwatch 1 - Tape measure 1 - 1U8865 Infrared Thermometer or 1 - 6V9130 Temperature Adapter Group
INDIVIDUAL OR GROUP EXERCISE
Perform relief valve pressure, cycle time and drift tests, and record your answers on the appropriate Lab C Worksheet for Off-highway Truck Hoist Test.
Page:
VI-10
777D Off Highway Truck CHAPTER : HOIST SYSTEM
LAB EXERCISES 769D-777D OFF-HIGHWAY TRUCK HOIST TEST Machine Model__________________________
LAB EXERCISES LAB D: TRACING HOIST SYSTEM OIL FLOW
BRAKE COOLING RELIEF VALVE
TO BRAKE COOLER
RAISE
HOIST RELIEF VALVE
HOIST RELIEF VALVE
LOAD CHECK VALVE
769D - 777D HOIST SYSTEM
Directions: Trace the flow of oil in the RAISE position using different colored pencils.
Page:
VI-12
777D Off Highway Truck CHAPTER : HOIST SYSTEM
POST TEST 769D-777D HOIST SYSTEM POSTTEST
Directions: Modified True/False. If a question is false, underline or circle the word or words that make the statement incorrect and replace with word(s) to make the statement correct. hoist system F Example: _____ 1. This is an engine class. ____ 1. Whenever work is performed under the body while the body is raised, you must install the safety pins AND disconnect the hoist control linkage. ____ 2. Incorrect adjustment of the hoist control linkage can prevent the transmission from shifting into reverse. ____ 3. Screens located on top of the hydraulic tank prevent contamination from entering the hoist system. ____ 4. The hoist system pilot operated relief valve controls the maximum pressure in the brake cooling system. ____ 5. An orifice plate at the rod end of the hoist cylinders prevents the body from raising faster than the pump can supply oil to the cylinders (caused by a sudden shift of the load). Directions: Multiple Choice. Circle the correct letter(s) of the best answer(s) for each question. 6. Supply oil from the hoist pump flows to the brake cooling system when the hoist lever is in the _____ position. A. B. C. D.
Raise Lower Hold Float
7. The _____ holds the hoist lever in the float position after the operator releases the lever. A. B. C. D.
ratchet pawl on the hoist lever centering spring on the directional spool ball detent on the directional spool small gremlin living in the hydraulic tank
Page:
VI-13
777D Off Highway Truck CHAPTER : HOIST SYSTEM
POST TEST 8. When the hoist valve is in the hold position with the body raised above the frame, the _____ will prevent the body from lowering. A. B. C. D.
directional spool orifice plate centering spring load check valve
9. If the hoist valve is moved from the hold to the raise position with the body raised above the frame, the _____ will prevent the body from lowering until pump supply pressure is higher than the pressure in the head end of the hoist cylinders. A. B. C. D.
10.When the hoist lever is in the _____ position, a small amount of oil pressure in the rod end of the hoist cylinders holds the body firmly down on the frame to prevent the body from bouncing when traveling without a load in the body. A. B. C. D.
Raise Lower Hold Float
Directions: Match the component with the correct location by placing the letter next to the component. ____
