TRAINING TIPS AND TACTICS
Module 3 - Truck Air and Brakes - Mechanical
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2
General information
Contents
System pressures Port numbers Use IMPACT Basic fault finding logic
Charging circuit
Circuit diagram - steel suspension Compressor Air dryer Governor valve Pressure regulator valve Multi Circuit Protection Valve (MCPV) Overflow valve
Rear circuit
Circuit diagram Footbrake valve Load sensing valve - steel suspension Load sensing valve - graph Load sensing valve - air suspension Load sensing valve - graph Spring brake chamber
Front circuit
Circuit diagram - with steel suspension Footbrake valve Quick Release Valve (QRV) Relay valve Pilot valve Circuit diagram - with air suspension Pilot valve graph
cont.
3
Park circuit
Circuit diagram Park brake control valve Blocking valve Connections at park brake tank Anti-compound valve Trailer brake control valve Spring brake chamber
Auxiliary circuit Circuit diagram High pressure system
Circuit diagram 7 port MCPV Pressure reduction - front and park circuit
Electronic Braking system (EBS) Circuit diagram ?????
Electronic Control Suspension (ECS) Solenoids and circuit diagram
Z Cam brakes Earlier S cam Z cam advantages Automatic adjustment Brake stroke Leading and trailing shoes Measuring lining thickness Shoe remove and refit Tappet components LH and RH components Initial setting of brake shoes Disc brake ????
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Introduction About this Pocket guide
This guide is intended as a memory jogger for the knowledge you have gained during your training course. The guide includes a summary of the material covered in: Module 3 - Truck Air and Brakes - Mechanical.
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Danger, Warning, Caution & Note
In this guide, risk of injury or damage is indicated by the following headings: DANGER - indicates a risk of serious personal injury or death. WARNING - indicates a risk of personal injury, or severe product damage. CAUTION - indicates risk of product damage. Note - draws attention to special methods or particular features. Read and implement all DANGER, WARNING and CAUTION instructions.
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Replacement parts
When replacement parts are required, it is essential that only Volvo genuine parts are fitted. If Volvo genuine parts are not used: - safety features embodied in the vehicle or components may be impaired. - performance and/or operation of the vehicle or components may be adversely affected. - Volvo warranty terms may be invalidated.
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Specification
Volvo are constantly seeking ways to improve their products, and alterations take place accordingly. Whilst every effort has been made to ensure the accuracy of this guide, it should not be regarded as an infallible guide to current specifications of any product. Neither Volvo, nor the supplier of this guide shall, in any circumstances, be held liable for inaccuracy or the consequences thereof.
Copyright
C
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, transmitted or copied without written permission from Volvo Truck & Bus Ltd. Volvo Truck & Bus Ltd. 2004
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General information 9
General information Air system
The complete truck air system has five main circuits: - charging circuit - front service circuit (footbrake) - rear service brake (footbrake) - park brake circuit - auxiliary circuit
High pressure system
Note: ʻHigh pressureʼ refers to the pressure in the tanks, and certain sections of piping. Not all parts of the system operate at high pressure - see the diagrams in ʻHigh Pressure Systemʼ. All post ʻ98 FM/FH trucks with air suspension have a ʻhigh pressureʼ system. Every tank has 12.0 bar pressure, except the park circuit tank, which has 8.5 bar.
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General information High pressure system - cont.
The high pressure system can be identified by a 7 port multi circuit protection valve (MCPV). Unless the truck has full air suspension, no air suspension tank is needed.
Low pressure system
All pre ʻ98 FM/FH trucks with air suspension, and all trucks with steel suspension have a ʻlow pressureʼ system. On trucks with air suspension, every tank has 7.5 bar pressure, except the wet tank which has 12.0 bar pressure. On trucks with steel suspension, every tank has 7.5 to 8.5 bar pressure. The low pressure system can be identified by a 5 port MCPV.
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General information Air pressure units
Port numbers - general
Air pressure can be expressed in ʻbarʼ or ʻPascalʼ: 1 bar = 100 Kpa (KiloPascal) 10 bar = 1 mPa (MegaPascal) Valve ports generally conform to a common numbering sequence: Port 1 - Supply, normally from a tank. If there is more than one supply, a second number is used - e.g. 11, 12. Port 2 - Delivery, to another component. If there is more than one delivery, a second number is used - e.g. 21, 22. Port 3 - Exhaust, to atmosphere. Port 4 - Signal to the valve to operate.
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General information
Use IMPACT
To ensure that you are using the latest service information - especially specifications - always get your information via IMPACT: Wheel brakes - group 51 Compressed air brakes - group 56
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General information Air is leaking from a valve.
Disconnect pipe(s) from outlet port(s) 2
Note: The valve may need to be operational. Operate park/footbrake
Is air leaking from the pipe ?
Yes
No
The component connected to the pipe is leaking. Trace the pipe back
Renew the valve
14
General information Basic air brake fault finding logic
The chart above shows the basic logic to be applied when air is leaking from a valve.
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16
Charging circuit 17
Charging circuit 23
1a
2a
24
1 14
3
2b
Charging circuit - steel suspension
18
Charging circuit Circuit with steel suspension
The components in this circuit are: 1 Compressor 1a safety valve 2a Air dryer 2b Regeneration tank - not with AIRDRY-E, version 2 trucks 14 Wet tank - if fitted 23 Test point 24 Multi-circuit protection valve
19
Charging circuit 23 1a
2a
24
1 14
2b
3 A
52a
B
52b
Charging circuit - air suspension (Pre 98)
20
Charging circuit Circuit with air suspension
The main components in this circuit are: 1 Compressor 1a safety valve 2a Air dryer 2b Regeneration tank - not with AIRDRY-E, version 2 trucks 14 Wet tank - if fitted 23 Test point 24 Multi-circuit protection valve 52a Pressure limiting valve 52b Pressure limiting valve A To suspension system B To suspension tank
21
Charging circuit
1COMP530
2COMP1080
22
Charging circuit Compressor
The compressor is driven by the engine timing gears. Two types of compressor are used from late 2001 onwards: - twin cylinder 2COMP1080 is used on all trucks with air suspension. - single cylinder 1COMP530 is used with steel suspension, where air consumption is lower.
Power reduction (PR)
The PR function relieves pumping pressure from the compressor, and thereby reduces the amount of power taken from the engine.
23
Charging circuit PR function - twin cylinder
When air pressure from the air dryer over-comes valve spring force, the sliding inlet and exhaust valves open. The open valves allow air to re-circulate from one cylinder to the other, only a very small amount of air is delivered to the air dryer. This small air flow is used to minimise oil pass-over from the compressor, and to cool and clean the air dryer exhaust.
PR function single cylinder
The PR function for a single cylinder compressor is similar to that for the twin cylinder, but the air passes into a dead volume in the cylinder head.
24
Charging circuit Compressor checks
Air inlet - the compressor must be able to draw in a sufficient amount of air to work efficiently. Always ensure that the air inlet is unobstructed. Delivery pressure - to check delivery pressure, fit a test gauge to the test point on the delivery pipe. Remember - the pressure will drop to zero when the compressor is unloaded. Charging time - (truck with rear air suspension), as a guide, with an engine speed of approx. 3000 rev/min, and an empty system, it takes approx. 3 minutes to reach max. pressure.
25
Charging circuit
Compressor checks - cont.
Air leaks - to isolate an air leak, always disconnect the trailer air connections. Before assuming that the compressor is a at fault, always check for: - air inlet obstruction. - leaks in pipes/ connections/other components. - correct governor valve operation. If the compressor has a PR function, disconnect the signal pipe from the compressor cylinder head, and check if the governor valve is signalling too early. Whilst the pipe is disconnected, check the mechanical operation of the PR valve by pressing against the piston to ensure that it moves smoothly and returns fully.
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27
Charging circuit
1
2
3 28
Charging circuit Air dryers
Air dryers are used to dry, clean and cool air from the compressor. They have a renewable cartridge filled with water absorbing granules - ʻdesiccantʼ. The cartridge usually has an oil separator which helps to remove oil passed over from the compressor. Oil contamination reduces the effectiveness of the desiccant. Four types of air dryer are in use - three single tower and one twin tower. All dryers - except AIRDRY-E - use a regeneration tank.
Single tower
1 Wabco 2 Haldex 3 Knorr These dryers have integral pressure regulating (governor) valves 29
Charging circuit
30
Charging circuit Twin tower
This is Wabco dryer, which has a remote mounted governor valve.
Dryer faults
The most common symptom of a faulty air dryer is slow air build up due to partial blockage of the cartridge. A completely blocked cartridge will allow no air flow, and will cause the safety valve in the compressor delivery pipe to blow-off.
Leaks single tower
Single tower dryers should not have any air leaks from the exhaust port when the compressor is charging. After the dryer unloads, it can take up to 30 sec. for the regeneration tank to discharge through the dryer exhaust. If discharge takes too long, a fault in the non-return valve is indicated.
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Charging circuit Leaks - twin tower
With this dryer, one tower is regenerating whilst the other is charging. The regenerating tower will leak a small amount of air when the other is charging. This small leakage is not a fault. If you are in doubt about how much air is leaking, it can be checked using tool 999 8050.
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33
Charging circuit 0
2
A
B
1 4
4
H
D C
1587 / 1939
K
J
A
2
F
G M
I + 15
L
E
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Charging circuit AIRDRY - E
This is an electronically controlled dryer fitted to version 2 trucks. This dryer uses the wet tank for regeneration. It is controlled by the vehicle ECU (VECU), and can be tested and calibrated using VCADS Pro. Note: Calibration must be carried out whenever the dryer cartridge or compressor is renewed. A - Compressor function B - Cooling coil C - Air dryer D - Vehicle ECU E - Wet tank
G - Unloader & PR J - Non-return valve K - Data bus L - Ignition feed M - Heating element
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Charging circuit AIRDRY - E - cont.
When the air dryer has reached operating pressure, solenoid (G) is energised allowing air to pass to the compressor to activate the ʻpower reductionʼ function. For regeneration, solenoid (F) is energised by the VECU, allowing some of the wet tank air to go back through the air dryer desiccant.
Air leaks
If air is leaking from the air dryer exhaust, disconnect all electrical plugs. Air leakage should stop. If it does not stop, the air dryer is faulty.
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37
Charging circuit
1 Supply from wet tank
P3
2 Output signal to air dryer port 4.
P2
3 Exhaust
P1 38
Charging circuit Governor valve
Cut out pressure Cut in pressure
The valve shown is a remote mounted type used with the Wabco twin tower air dryer. A common location is at the side of the battery box. The governor valve controls the compressor output. When system pressure reaches that set by the governor valve, port 2 is opened, and system pressure - entering the valve via port 1 - is fed back to the air dryer and compressor. This cut out pressure opens the compressor inlet valves, and air compression stops. When system pressure falls below the valve setting - cut in pressure - port 2 is closed so system pressure is no longer fed from the valve. The compressor valves now close and air compression starts again.
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Charging circuit Governor valve faults
A faulty governor valve will cause one of two symptoms: - system pressure too low. - system pressure too high, which will cause the safety valve to blow. Use IMPACT to find the correct pressures.
Checking cut out pressure
Connect a pressure gauge to the wet tank, and release some of the pressure. Start the engine, and build up pressure until the compressor is unloaded, and the gauge reading is no longer rising - this is cut out pressure.
40
Charging circuit Checking cut in pressure
Release pressure from the wet tank a little at a time. The pressure reading will fall, and then start to rise - this is cut in pressure, which should be approx. 1 bar to 1.5 bar lower than cut out pressure.
Adjusting the pressure
Note: Only cut out pressure can be adjusted. If cut out pressure is correct, but cut in pressure is not, the valve must be renewed.
Remote mounted valve
To raise the cut out pressure, turn the adjusting screw outwards - anti-clockwise.
Integral valve
To raise the cut out pressure, turn the adjusting screw inwards - clockwise.
41
Charging circuit
42
Charging circuit
Pressure limiting valve
The pressure limiting valve, fitted before the 4 circuit protection valve, limits the maximum pressure allowed into the brake circuits. It is fitted mainly to trucks with air suspension. With an empty system, the valve is fully open, and closes when the set pressure at port (2) is reached.
Pre ʻ98 types
Pre ʻ98 valve types - identifiable by the long bolt in one end - are adjustable. The valve allows a wet tank pressure of 12 bar, and limits pressure in the brake circuits to approx. 7.5 bar. Port numbers; 1 - Supply from wet tank 2 - Delivery to port 1 of MCPV.
43
Charging circuit
P1 P2
44
Charging circuit Truck version 2 valves
Valves fitted to truck version 2 are not adjustable. The valve reduces the pressure to the footbrake valve and MCPV - ports (11) and (12). Port numbers; 1 - Supply from service tank 2 - Delivery to footbrake valve and MCPV. Use IMPACT to find the correct pressure.
Checking the pressure
Connect a pressure gauge to the front or rear brake tank, and release pressure down to approx. 5 bar. Start the engine, build up pressure, and note the maximum pressure in the tank.
45
Charging circuit
46
Charging circuit
Multi circuit protection valve - MCPV
The MCPV - or 4 circuit protection valve - separates the 4 main circuits to ensure that a leak in one circuit does not affect any other circuit. The MCPV also ensures that the air tanks charge in the correct sequence. 5 port valves are fitted with steel suspension (low pressure system). 7 port valves are fitted with air suspension (FM/FH) from ʻ98. See ʻHigh pressure systemʼ.
Port numbers - pre ʻ98
1 Supply in from wet tank. 21 Delivery out to rear service tank. 22 Delivery out to front service tank. 23 Delivery out to park tank. 24 Delivery out to auxiliary manifold (Note: no tank)
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Charging circuit
Port numbers - post ʻ98:
Valve versions - 5 port
1 Supply in from wet tank. 21 Delivery out to front service tank. 22 Delivery out to rear service tank. 23 Delivery out to park tank. 24 Delivery out to auxiliary manifold (Note: no tank)
There have been four versions of the 5 port valve, the design of which affects the charging sequence or drain back features.
48
Charging circuit Version 1
Tank charging sequence: One of the service circuits > park > auxiliary > the other service circuit. This meant that the truck could be driven with only one service circuit completely filled. EU legislation then demanded that vehicles be capable of stopping within a defined distance as soon as the vehicle could be driven - i.e. when the park brake was released - so version 2 was introduced.
Version 2
This valve has by-pass channels in the front and rear service circuits, which allow the charging sequence: Both service circuits, at the same time > park > auxiliary.
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Charging circuit It was then noted that, a truck parked overnight could leak air from one of the service circuits which, again, meant that the truck could be driven with only one service circuit completely filled - so version 3 was introduced. Version 3
This valve has a choke valve fitted in port 22 - rear service circuit. If this circuit leaked down to 2.9 to 3.4 bar, the choke valve allowed the park tank to leak to atmosphere via a vent on top of the valve between the four ports. Note: This leak - whenever rear service pressure is less then choke valve activation pressure - is normal, and IS NOT a fault.
50
Charging circuit However, many technicians thought this leak was a fault, and renewed the valve - so version 4 was introduced. Version 4
This valve still has the choke valve fitted but, instead of leaking to atmosphere, the park tank drains into the rear service tank. This valve is in current use - all version 2 trucks have this valve fitted..
Has the valve got by-pass channels ?
To check if an MCPV has by-pass channels: Connect test gauges to the wet tank and front and rear service tanks. Completely drain the air system and start the engine If both service tanks charge at the same time, the valve has by-pass channels.
51
Charging circuit Has the valve got a choke drain valve ?
To check if an MCPV has a choke drain valve: Connect test gauges to the rear service tank and park tank. Release pressure in the rear service tank down to approx. 3 bar.
Valve version 3
If park tank air now leaks from the exhaust port - in the centre of the MCPV four elements - a choke valve is fitted.
Valve version 4
If park tank air now drains into the rear service tank - a choke valve is fitted. Note: This is a normal function of the valve - the valve is NOT faulty.
52
Charging circuit MCPV without choke drain valve
MCPV common faults
Note: When draining either service tank, the park tank must not drain at all. If it does, the non-return valve is faulty, and the complete 4 circuit protection valve must be renewed. Input blocked - no build-up of brake systems. One element stuck closed - no build-up of one brake system. Air leak - valve faulty (But! remember the choke valve operation)
53
Charging circuit
Note porting differences in this area
P1
P2 54
Charging circuit Overflow valve
Two types Type 52a
Opening pressure - to system Ports
This valve is fitted only to trucks with air suspension. It is normally located on a crossmember under the 5th. wheel. This valve is always fitted to trucks with air suspension, and has no return flow. The valve ensures that the braking system reaches a predetermined pressure before it opens and allows air to enter the suspension system. Version 1 trucks - 6.7 to 7.0 bar. Version 2 trucks - 7.0 to 7.3 bar. Port 1 - supply from wet tank. Port 2 Delivery to air suspension system
55
Charging circuit
56
Charging circuit Easy check type 52a valve
Completely drain the air system, including the air suspension system, so that the chassis is sitting on the suspension bump stops. Connect test gauges to the wet tank and the test point on the delivery from 52a. Start the engine, and watch the gauges. When pressure in the wet tank reaches the opening pressure of 52a, the gauge on 52a delivery should start to rise. The air bags should start to fill, raising the chassis.
57
Charging circuit
Note porting differences in this area
17
P1
P2 58
Charging circuit Type 52b
Opening pressure - to tank Ports Return flow
This valve is fitted to trucks with an air suspension tank, downstream from 52a, and has a return flow path. The valve ensures that the air bellows are filled before the air tanks, so that the truck reaches normal ride height as soon as possible. Version 1 trucks - 10.0 to 10.4 bar. Version 2 trucks - 10.0 to 10.3 bar. Port 1 - supply from 52a. Port 2 - delivery to air suspension tank. The valve has full return flow, so that air can pass from outlet (2) through non-return valve (17) to inlet (1) if pressure is lower in this connection - i.e. if the driver operates the control to raise the suspension.
59
Charging circuit
1
2
3
60
Charging circuit
Three versions
There are three versions of the valve.
Version 1
Version 1 is fitted to FL10 and pre ʻ98 FH.
Version 2
Version 2 is fitted to FM/FH version 1 trucks.
Version 3
Version 3 is fitted to FM/FH version 2 trucks.
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62
Rear circuit 63
Rear circuit 12
37 24 4
10
30
4
33
33
S P
2 56
64
Rear circuit Main components
The main components in the rear brake circuit are: 10 Foot brake valve 12 Rear service tank 30 Anti-compound valve ? Load sensing valve 33 Spring brake chambers ?? ABS valves ?? Trailer brake control valve 56 Air bags
65
Rear circuit P12
P22
P11
P21
P
66
Rear circuit Footbrake valve Primary circuit
Ports - non EBS
The footbrake valve is divided into two separate circuits - primary and secondary. The primary circuit is always nearest to the brake pedal, and - except with EBS and early FL6 - the primary circuit is always the rear circuit. Port 11 - supply from rear tank Port 12 - supply from front tank Port 21 - delivery to load sensing valve port 4, anticompound valve, and trailer brake control valve. Port 22 - delivery to front circuit quick release valve Port 3 - Exhaust P = Pedal end
67
Rear circuit P12
P22
P11
P21
P
68
Rear circuit Ports - EBS
Port 11 - supply from front tank Port 12 - supply from rear tank Port 21 - delivery to front modulators Port 22 - delivery to rear modulator Port 3 - Exhaust P = Pedal end
Air leaks - non EBS
Air leaks from the valve exhaust port (3): If the leak stops when the park brake is applied, the footbrake valve is OK. If the leak does not stop when the park brake is applied, the footbrake valve is faulty and should be renewed.
69
Rear circuit
Port 21 pipe
Air leaks from the valve exhaust port (3) only when the park brake is OFF: Disconnect the pipes from ports 21 and 22. If air is escaping from the port 21 pipe, the most likely causes are: - faulty anti-compound valve. Confirm by disconnecting the pipe from the service port - faulty trailer brake control valve. Confirm by disconnecting the pipe from port 41.
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Rear circuit Port 22 pipe
If air is escaping from the port 22 pipe, the most likely causes are: - faulty trailer brake control valve. Confirm by disconnecting the pipe from port 42. - faulty front spring brake chamber. Confirm by disconnecting the pipe from port 11 on each chamber.
71
Rear circuit
P4 P2 P1 L
P2 72
Rear circuit
Load sensing valve Valve with steel suspension
The load sensing valve adjusts the air pressure to the rear brake chambers in proportion to the load on the vehicle. The illustration above shows the type of valve used with steel suspension. This valve has an integral relay valve. Note: Some very early trucks - e.g. FL6 - have separate load sensing valve and relay valve. Output pressure is determined by spring deflection, which is mechanically communicated to the valve via a rod and lever (L).
Ports
Testing
Port 1 - supply from rear brake tank Port 2 - delivery to rear brake chambers Port 3 - exhaust Port 4 - signal from footbrake primary circuit - port 21 Connect test gauge to : - rear brake chamber - primary circuit signal - port 4
73
Rear circuit P out +/- 0.4 bar
Input pressure - from footbrake - 7 bar
Lever deflection - mm
8
80
7
70
6
60
5
50
4
40
f
3 2
20
f L = 80 mm +/- 2 mm
10
1 0
30
1
0
2
4
6
8
10 12 14 16 18 20
00
Bogie load - ton
74
Rear circuit Load sensing valve graph steel suspension
The operating length (L) of valve operating lever (1) must be accurately set to 80 mm +/- 2 mm. On the graph above, ʻfʼ represents deflection of lever (1). ʻfʼ can be used to work out how much load has been added to the truck: Measure lever deflection before and after adding load.
Example
If deflection changes by 20 mm, approx. 12 tonne has been added. Note: This calculation is accurate only when springs are new.
75
Rear circuit P4 P1
P2 P3
P42
P41
76
Rear circuit
Valve with air suspension
The illustration above shows the type of valve used with air suspension. This valve has an integral relay valve. Output pressure is determined by the pressure in the rear air bags, which is sensed at ports (41) and (42).
Ports
Testing
Port 1 - supply from rear brake tank Port 2 - delivery to rear brake chambers Port 3 - exhaust Port 4 - signal pressure from footbrake primary circuit - port 21 Port 41 - load signal from air bags Port 42 - load signal from air bags
Connect test gauge to : - rear brake chamber - primary circuit signal - port 4 - air bag signal - ports 41 and 42
77
Rear circuit P out +/- 0.4 bar
bar 8
Input pressure 7 bar
4 x 2 truck
7 6
P Out
5 4
P Air bag
3 2 1 0
0
2
4
6
8
10 12 14 16 18 20
Bogie load - ton
78
Rear circuit Load sensing valve graph - air suspension 4x2
In the example above, air pressure in the rear air bags has been measured at approx. 2 bar. Find 2 bar on the LH scale. Follow the horizontal line until it intersects the ʻP Air bagʼ graph line. Move vertical up to the ʻP Outʼ graph line. Move left to the LH scale and read the value. This is the pressure required in the rear brake chambers. Note: That output pressure is governed around a constant input pressure of approx. 7 bar.
79
Rear circuit
80
Rear circuit
Valve with air suspension and drive and pusher axles Ports
The illustration above shows the type of load sensing valve used with air suspension, on a truck with drive and pusher axles. This valve has an integral relay valve. Output pressure is determined by the pressure in the rear air bags, which is sensed at ports (41) and (42). Port 1 - supply from rear brake tank Port 2 - delivery to rear brake chambers Port 3 - exhaust Port 4 - signal from footbrake primary circuit - port 21 Port 41 - load signal Port 42 - load signal
81
Rear circuit 8 7 6 5 4 3 2 1 bar 0 7 6 5 4 3 2 1 0
Pneumatic load sensing valve - bar +/- 0.4 P Brake P Air bag
Pusher/tag axle Input brake pressure is output from drive axle ʻP brakeʼ Drive axle Input brake pressure - 7 bar
P Brake P Air bag
0
2
4
6
8
10 12 14 16 18 20 22
Bogie load - ton
82
Rear circuit
In the example above, air pressure in the drive axle air bags has been measured at approx. 1.5 bar. Find 1.5 bar on the LH scale. Follow the horizontal line until it intersects the drive axle ʻP Air bagʼ graph line. Move vertical up to cut all three graph lines. At each point where a graph line is cut, move left to the LH scale and read the value.
83
Rear circuit 1
3
2
Drive
P11
P12
4
Park
84
Rear circuit Spring brake chamber operation
The spring brake chamber is two chambers back to back - one for footbrake operation and one for park brake operation.
Drive
At ʻdriveʼ position, air is fed to the spring brake chamber (1) via port (12). Spring (2) is compressed, and no force is applied to the brakes.
Park
At parkʼ position, air is released from spring brake chamber (1), via the exhaust port on the park brake control valve. Spring (2) exerts a force on piston (3), and the brakes are applied via push rod (4).
85
Rear circuit 5
5
Service
5 P11
P12
Mechanical release
86
Rear circuit Service
Mechanical release
No brakes ! -chock wheels
When the footbrake is applied, air enters service chamber (5) via port (11). Air pressure acts on diaphragm (6) and the brakes are applied via push rod (4). The parking brakes can be released without air pressure. Mechanical release may be needed during repairs or vehicle recovery. DANGER Chock wheels before brake release. If there is no air in the system and the brakes are mechanically released, there will be no brakes at all. If there is air in the system and the brakes are mechanically released, there will be no parking brake. To release the brakes, turn bolt (7) fully anti-clockwise. CAUTION Do not use air/power tools on the bolt.
87
Rear circuit 1
2 Air leak points
3
Common air leak points are: 1 Push-rod seal. 2 Diaphragm - via the ʻtell-taleʼ hole. 3 Spring brake piston seal.
88
Rear circuit Leak check - service brakes
With the footbrake applied, check for leaks at the tell tale hole, and push-rod. Leaks from these points indicates a ruptured service diaphragm, which can be renewed as a separate part.
Renew diaphragm
Fully unscrew the release bolt. Note: On new type chambers, with captive nut, 45 turns will fully release the bolt. Remove the clamp bolt and clamp, and renew the diaphragm.
No park brake !
DANGER Bolt must be screwed fully back in after repairs. If this is not done, there will be no park brake. Note: On new type chambers, with captive nut, turn bolt 45 turns until it stops, and the red plunger is fully down.
89
Rear circuit Leak check - park brakes
1
Seal (1) around the park brake piston normally prevents air transfer from the park brake chamber to the service brake chamber. If this seal leaks, air will leak from the load sensing valve/ relay valve, or a brake modulator, when the park brake is released.
90
Front circuit 91
Front circuit 11
33
12 33
2 7
24
14
7
33
8
P12 P11
10 S P
P22 P21
33
92
Front circuit Main components - circuit with steel suspension
The main components of the front brake circuit are: 10 - footbrake valve - front circuit section ?? - quick release valve (or relay valve if pilot valve fitted) ??- pilot valve (if front air suspension fitted) 33 - brake chamber 11- front circuit air tank ??- pressure limiting valve
93
Front circuit 12
22
11
21
P
94
Front circuit Footbrake valve Primary circuit
The footbrake valve is divided into two separate circuits - primary and secondary. The primary circuit is always nearest to the brake pedal, and - except with EBS and early FL6 - the primary circuit is always the rear circuit. P = Pedal end For more information about the footbrake valve, see ʻ Rear Circuitʼ.
95
Front circuit P1 2
P4
P4 P3
96
Front circuit Quick release valve
The quick release (QRV) valve is located close to the brake chambers. This location provides a short path for exhaust air from the chambers, so the brakes rapidly release. A QRV may be fitted in the front brake circuit, park brake circuit or both circuits.
QRV - front circuit
When the footbrake is applied, air pressure entering at port (1) pushes down diaphragm (2) to close off exhaust port (3). Air passes to the brake chambers via ports (4). When the brake is released, air is exhausted at the footbrake valve, and pressure at port (1) is removed. Diaphragm (2) is pushed up by exhaust air pressure entering via ports (4). Valve exhaust port (3) is opened and air is rapidly released from the brake chambers.
97
Front circuit P1 P4
P4
P3
Park brake applied
Park brake released 98
Front circuit QRV - park circuit
When the park brake is released, air pressure entering at port (1) pushes down diaphragm (2) to close off exhaust port (3). Air passes to the brake chambers via ports (4), compressing the coil spring to release the brakes. When the park brake is applied, air is exhausted at the park brake valve, and pressure at port (1) is removed. Diaphragm (2) is pushed up by exhaust air pressure entering via ports (4). Valve exhaust port (3) is opened and air is rapidly released from the brake chambers, allowing the coil spring to apply the brakes.
99
Front circuit P4
P2
P2 P3
100
Front circuit Relay valve
Like the QRV, the relay valve is located close to the brake chambers for rapid brake application and release. A relay valve may be fitted in the front brake circuit, rear brake circuit, park brake circuit or all circuits. When front load sensing is fitted - long wheelbase 4 axle trucks -the QRV is replaced by a relay valve, controlled by a pilot valve.
Relay valve ports
Port 1 - supply from air tank - front, rear or park Port 2 - to brake chambers - service or park Port 3 - exhaust Port 4 - signal - via anti-compound valve - from either footbrake valve port 21 or 22, or from park brake valve Port 21
101
Front circuit P4
P2
P2 P1 P3
Brakes OFF
Brakes applying
Brakes applying
- supply (1) closed
- supply (1) closed
- supply (1) open
- exhaust (3) open
- exhaust (3) closed
- exhaust (3) closed
Relay valve function
102
Front circuit
Brakes held
Brakes released
- supply (1) closed
- supply (1) closed
- exhaust (3) closed
- exhaust (3) open
Relay valve function
103
Front circuit Relay valve leaks
Air leaks from the exhaust port when the footbrake is applied: - the relay valve is faulty, and must be renewed.
Air leaks from the exhaust port when the footbrake is released: - the most likely cause is a faulty brake chamber. Confirm this by disconnecting the pie from port (11) from each chamber.
104
105
Front circuit P1 P4 P2 P
106
Front circuit Pilot valve
Ports
Long wheelbase rigid trucks with 4 axles have a tendency for front wheel brakes to lock when the truck is unladen or partially laden. To counteract this tendency, a pilot valve is fitted in conjunction with a relay valve. The pilot valve acts as a load sensing valve for the front axles, and is controlled by a signal from the rear load sensing valve. Port 1 - supply from footbrake port (22) Port 2 - delivery to front relay valve port (4) Port 4 - signal from rear load sensing valve port (2) P - plugged Note: If the rear load sensing valve is incorrectly set, the front brake pressures will be incorrect.
107
Front circuit
33
33
8
3
11
7 7
2 10 S
33
33
P
9
S
108
Front circuit Main components circuit with front air suspension
The main components of this circuit are: 10 Foot brake valve 11 Front service tank ?? Quick release valve, or relay valve ?? Pilot valve 33 Brake chambers ?? ABS valves ?? Trailer brake control valve ?? Rear load sensing valve S Signal to pilot valve
109
Front circuit Input pressure P= 7 bar Pressure at front brake chambers - bar
A copy of the graph is located either behind the grill, or on the driverʼs door
7 6 Signal pressure from rear load sensing valve - bar
5 4
0
1
2
3
4
5
6
7
110
Front circuit Pilot valve graph
Test points
The pilot valve is not adjustable. If pressures do not correspond with the above graph, the valve must be renewed. Test gauge positions: - top of rear load sensing valve - port 4 - front brake chamber - rear brake chamber, this pressure reading represents the signal pressure to the pilot valve - i.e. the bottom scale of the graph. Locate this pressure on the bottom scale, then move vertical to intersect the plot. Move left to the left hand scale - this is the pressure that should be in the front brake chambers. In the example shown, a signal pressure of approx. 3.5 bar should produce a front chamber pressure of approx. 5.75 bar.
111
Front circuit Pilot valve faults
Air leak from pilot valve exhaust port when footbrake is applied: - pilot valve is faulty, renew valve.
Front brakes slow to release:
- check/clean exhaust silencers.
Front brakes slow to release - exhaust silencers OK:
- disconnect the pipe from port 2 and lightly press - then release - the footbrake. Air flow should stop as soon as the footbrake is released.
112
Park circuit 113
Park circuit
13 24 14 2b
17 19
31
30
33
33
114
Park circuit Main components
The main components in the park brake circuit are: 13 Park brake air tank 17 Blocking (Bromse) valve 19 Park brake control valve 30 Anti-compound valve (Shuttle valve) (2-way valve) 31 Park brake relay valve 33 Spring brake chambers ?? Rear load sensing valve ?? Trailer brake control valve
115
Park circuit
P2 P1 P3
116
Park circuit Park brake control valve - FL & Bus Ports
This park brake valve is fitted to FL6 rigid trucks, and buses.
Port 1 - supply Port 2 - delivery Port 3 - exhaust The valve has 2 operating positions - ON and OFF. There is no secondary, or ʻprogressiveʼ function.
117
Park circuit
118
Park circuit
Park brake control valve FM/FH Ports
This park brake valve is fitted to FM and FH trucks. Port 11 - supply from park brake tank, via non-return valve and blocking valve Port 21 - delivery to signal park brake relay valve Port 22 - delivery to signal trailer brake control valve The valve has 3 operating positions - ON, SECONDARY and OFF. In ON position, no air is delivered from port 21, but air is delivered from port 22 to ensure that the trailer control valve remains closed - so no air is supplied to the yellow line. In the full secondary position, no air is delivered from either port 21 or port 22. In OFF position, air is delivered from ports 21 and 22.
119
Park circuit P2
P
P1 120
Park circuit Blocking valve
Ports
The blocking valve is a safety device which ensures that the driver has to press the valve button in to supply air to the park brake circuit to release the brakes. The button cannot be pushed in until pressure in the service tanks is normal. When pressure in the park tank or wet tank falls to approx. 5 bar, an internal spring pushes the blocking valve piston out. Port 1 - supply from park brake tank Port 2 - delivery to park brake control valve P - Push button in
121
Park circuit 15
13
1a 2 3
122
Park circuit
Connections at park brake tank
1a Safety valve 13 Park brake tank 15 Non-return (one-way) valve 2 Trailer brake connection 3 Park brake connection
Testing the park brake valve
Disconnect the pipe from port 43 on the trailer control valve. When the park brake control is at ON position, and also when it is at OFF position, air should be present. When the park brake control is at SECONDARY position, no air should be present.
123
Park circuit P3
P1
P2 P2
4
P3
P1 P3
Ports shown as per valve orientation
P2 in park circuit diagram
124
Park circuit Anticompound Ports
This valve may also be referred to as - ʻ2-way valveʼ ʻshuttle valveʼ Port 1 - park brake circuit Port 2 - footbrake circuit Port 3 - signal pressure to park brake relay valve The valve prevents ʻcompoundingʼ of park brake and footbrake pressures - i.e. both pressures being applied to the spring brake chambers at the same time. The valve has a free moving piston (4) which can close off either port (1) or port (2).
Operation
When the park brake is applied, air is exhausted from the park circuit, via the relay valve and park brake control valve, allowing the spring to apply the brakes. If the footbrake is now also applied, pressure at port (2) pushes the piston over to close off port (1).
125
Park circuit Operation cont.
Footbrake pressure is now also admitted to the park brake chambers, reducing the force exerted by the spring.
Testing the valve
Apply the park brake, and note the position of the brake operating levers. Watch the levers, and apply the footbrake. The levers should not move any further in the application direction.
126
127
Park circuit
P41 P22 P43
P21
P42
P
128
Park circuit
Trailer brake control valve - early type Ports
This valve is used to control trailer braking.
Port 41 - rear Port 43 - park (port 22) Port 42 - front Port 22 - red trailer line Port 21 - yellow trailer line P - from park brake tank
Adjustment
Turn adjustment screw clockwise to increase pressure to trailer.
129
Park circuit
130
Park circuit
Trailer brake control valve version 2 trucks Ports
This valve is used to control trailer braking. Port 1 - supply from park brake tank Port 21 - delivery to red trailer line Port 22 - delivery to yellow trailer line Port 41 - signal from rear service brake - port 21 Port 42 - signal from front service brake - port 22 Port 43 - park brake signal from park brake control valve
Adjustment
Turn plastic adjustment screw anti-clockwise to increase pressure to trailer.
Dump valve
This trailer valve has an internal dump valve. If the yellow trailer line is fractured, the dump valve allows the red trailer line to be dumped via the yellow line.
131
Park circuit Testing the trailer brake control valve
Test gauge positions: - Primary brake signal at rear load sensing valve. - Yellow trailer line. Note: It is essential that the input pressure is reached whilst the foot brake is being APPLIED - not being RELEASED. If the required input pressure is exceeded whilst the footbrake is being applied, the brake must be fully released, and applied again.
132
133
Park circuit
P12
134
Park circuit
Spring brake chamber
Remember !
1 Push-rod 2 Service diaphragm return spring 3 Service brake chamber - nearest to the push rod 4 Service brake diaphragm 5 Captive nut 6 Park brake chamber piston 7 Park brake application spring 8 Park brake chamber - furthest from the push rod 9 Park brake mechanical release bolt Park brake ON = air OUT of park chamber = spring applies brake. Park brake OFF = air IN to park chamber = spring compressed. Foot brake ON = air IN to service brake chamber = air applies brake. Footbrake OFF = NO air to service brake chamber.
135
Park circuit Brake chamber faults
With the system at full pressure, and the blocking valve pushed in, release the park brake. Disconnect the pipe from the service brake chamber. There should not be any air escaping from the chamber. Check for leaks around the wind off bolt - there should not be any escaping air. For more information about operation of the spring brake chamber, see ʻRear Circuitʼ.
136
Auxiliary Circuit 137
Auxiliary circuit
P24
24
138
Auxiliary circuit The auxiliary circuit includes - e.g. drivers seat, clutch, gearbox air system, air horns. The circuit is fed from port (24) of MCPV (1), via in-line air filter (??).
139
140
High Pressure System 141
High pressure system Thick lines = HIGH pressure Thin lines = low pressure
11 P21
12
P1
P11
51
2b 10
P12
P23
14
P22
P24
24
61 56
S P
142
High pressure system
Air suspension
Pressure limiting valves
The ʻhigh pressureʼ referred to is the pressure in wet tank (14) and service brake tanks (11) and (12) and associated pipe work, shown by thick lines. The pressure in these circuits is 12 bar. The extra pressure means that - for a given volume - the tanks contain more air. The high pressure system has been introduced so that - on trucks with rear air suspension only - a separate air suspension tank is not required. This gives weight and cost savings. Note: On trucks with air suspension at front and rear, an air suspension tank is still required. Pressure limiting valves (51) and (61) reduce the pressure to 8.1 to 8.5 bar, so all circuits after these valves operate at this pressure. Note: This does not apply to trucks with EBS.
143
High pressure system High or low pressure
On all pre ʻ98 trucks, the complete air system operated at low pressure. On all post ʻ98 trucks, the circuits shown in the previous diagram operate at HIGH pressure - except - if the truck has steel suspension all round. In which case the complete air system operates at low pressure. This means that - if fitted with air suspension - all FM and version 2 FH operate at HIGH pressure.
144
EBS 1 21
22
11
12
23
24
145
EBS 7 port MCPV
The 7 port MCPV shown above is used with high pressure systems. Port 1 - HP supply from wet tank (14) Port 11 - LP supply from pressure limiting valve (51) Port 12 - LP supply from pressure limiting valve (61) Port 21 - HP delivery to front service tank (11) Port 22 - HP delivery to rear service tank (12) Port 23 - LP delivery to park tank and trailer brake valve Port 24 - LP delivery to ?? (25) Note: The 2 extra ports - (11) and (12).
146
EBS 7 port MCPV - cont.
In common with the 5 port valve, used with low pressure systems, there have been a number of versions of this 7 port valve.
Version 1
This is the original valve, with no choke drain.
Version 2
This valve has a choke drain to atmosphere.
Version 3
This valve has a choke drain to the rear service tank. The function of the choke drain valve is the same as for the 5 port valve.
147
EBS P21
P22
1
11 24
P11
51 new type
P12 P24
P23
S P21
P
10
P11
37 51 early type
25 13
148
EBS
Pressure reduction - front and park circuit
The illustration above shows how pressure is reduced. MCPV (24) is supplied with air at 12.0 bar via port (1). Air is delivered to front service tank (11) via port (21). From tank (11), air enters pressure limiting valve (51) via port (1). Air at 7.5 bar is delivered from valve (51) via port (2), and is fed to MCPV port (11). Air is delivered from MCPV port (23) to park tank (13), and to trailer control valve (37). A tee off the MCPV supply line feeds the front brake circuit supply of footbrake valve (10). On non EBS systems, the feed is to port (12) - secondary circuit. On EBS systems, the feed is to port (11) - primary circuit. Note: New type pressure limiting valve is fitted to version 2 trucks, and is not adjustable. Delivery pressure is controlled at 8.1 to 8.5 bar. 149
Electronic Braking system - EBS 150
EBS Thick lines = HIGH pressure Thin lines = low pressure
11
12
P11 P23
14 2b
51
P1
P21
24
P22 P12
61 56
S P
10
151
P21
33
37
P22
24
P11 P23
37
P1
P12
37 33
P24
13 S P
25 30
37
31
33
33
High pressure system - EBS
152
EBS
Info/illust reqʼd
153
EBS
154
Electronic Controlled Suspension - ECS 155
ECS 23
22
22
21
22
21
4 1/3 21
3
1
1
3 156
P23
P22
P1/3
P4
56
56
56
P21
Y25
P22
P22
P21
P21
P1
P1
56 Y29 52a
56
14
56
56 157
ECS P22
P23
P22 P21 P22
P21
P4 P1/3
P21
P3
P1
P1
P3 158
ECS
Ports
Front axle solenoid
1/3 Supply air and drain to drive axle solenoid (port 23) 21 Delivery to LH front air bag 22 Delivery to RH front air bag 4 Supply from wet tank for solenoid valve control
Drive axle solenoid
1 Supply from overflow valve (52a) 21 Delivery to LH drive axle air bag 22 Delivery to RH drive axle air bag 23 Delivery to front axle solenoid valve - plugged if rear air suspension only
Pusher axle solenoid
1 Supply from overflow valve (52a) 21 Delivery to pusher axle suspension air bags 22 Delivery to RH lift air bag
159
160
Z Cam Brakes 161
Z cam brakes
1
162
Z cam brakes Earlier S cam Inefficient Disadvantages
The forerunner to Z cam brakes was S cam. Compared to the Z cam design, the S cam was not a very efficient brake. The main disadvantages are: - as shown in the diagram above, shoe contact force is very uneven, diminishing rapidly towards the anchor end. This is largely because the shoes pivot on anchor pins (1), and so are not free to self-centre. - the only time when contact forces are more even is when the lining is almost worn out. - bedding in new linings takes a long time. - there is a risk of the cam going over-centre when drum/ linings are worn.
163
Z cam brakes 3
5
1 2
1 3
5
4
164
Z cam brakes Z Cam
Even contact area
Brake shoe movement is controlled by a ʻZ camʼ arrangement, which describes the Z shape formed by struts (1) resting in cam (2). Cam (2) is rotated by the brake lever, and struts (1) push out tappets (3) to force the brake linings into contact with the drum. Because they are free to move on the tappet heads and abutments, the brake shoes are self -centring. This arrangement ensures more even lining to drum contact, and provides much more efficient braking. The shoes are retracted by spring (4), acting on pins (5), when air pressure is released.
165
Z cam brakes
A
B
166
Z cam brakes Automatic adjustment
The Z cam expander assembly includes an automatic adjustment mechanism, which compensates for brake lining wear. When wear clearance needs to be taken up, operation of the brakes causes pinion (5) to rotate leading shoe tappet screw (6). Cross-shaft (7) relays this rotation to trailing shoe tappet screw (3). During the final part of brake release, the tappet screws unscrew from the tappet heads by a small amount, and the brake shoes are moved closer to the drum. A - tappet with new linings B - tappet with worn linings Initial setting of the lining to drum clearance is achieved by pushing in, and turning adjuster stem (8).
167
Z cam brakes S
168
Z cam brakes Brake stroke
Correct brake strokes (S) are very important, for correct operation of the brakes. The correct stroke for any particular vehicle is determined by: - brake chamber type and size - lever length - air pressure in the chamber Because of these factors, the stroke is different from model to model.
Use IMPACT
Use IMPACT to find the correct stroke for the vehicle you are working on.
169
Z cam brakes
A
A
170
Z cam brakes Leading and trailing shoes
Each wheel assembly has a leading - or ʻprimary (P) shoe, and a trailing - or ʻsecondary (S)ʼ - shoe. The linings are offset on the shoes, leaving a gap between the end of the lining and the end of the shoe, facing the direction of rotation. Arrows (A) on the end of the shoe indicate the correct direction of drum rotation.
171
Z cam brakes
A
B
172
Z cam brakes Shoe location
Because they are different, brake shoes must be correctly located. The smooth radius (A) at one end of the shoe ALWAYS fits against the tappet. The notched end (B) fits against the fixed abutment. Wear will eventually cause a flat spot on the radiused end of the shoe. This can prevent free floating of the shoe, leading to brake judder and squeal. The maximum allowable flat spot length is 30 mm.
173
Z cam brakes
174
Z cam brakes Measuring lining thickness
The thickness of lining material can be measured through the four inspection holes in the brake backplate. If access is difficult, it may help to get an accurate measurement by winding off the brake using the manual adjuster. To wind off the brake, first push in the adjuster stem. Count the number of turns, and turn the stem in the same direction as forward drum rotation. Reset the brake shoe adjustment after measurement. CAUTION To prevent dirt getting into the brake mechanism, refit the covers in the inspection holes.
175
Z cam brakes P
999 8550 P
176
Z cam brakes
Shoe remove and refit
CAUTION To avoid damage to the ABS pole wheel, spring expansion tool 999 8550 must be used. Expanding the tool relieves spring pressure from return pins (P), allowing them to be withdrawn and refitted during shoe remove and refit. CAUTION Do not apply the park brake or footbrake when the brake drum is not fitted. The expander mechanism may be damaged. If the drum is to be left off for a long period, wind off the spring brake. This will prevent damage if there is loss of air which would normally cause the brake to come on.
177
Z cam brakes 1 2 3 4 5
250 mm
6
7
178
Z cam brakes Tappet components
When relining
Retraction spring
1 Tappet screw cover 2 O-ring 3 Stop ring - prevents tappet from over-adjusting 4 Tappet head
5 Tappet screw 6 Tappet seal 7 Strut
Check condition of tappet screw cover, and tappet seal Renew any damaged component. If the adjuster is dismantled, ensure components are lubricated with the correct high temperature grease. Because auto. adjustment takes place during the last part of shoe retraction, spring (1) must fully retract the shoes, so the spring must not be weakened or deformed in any way. The gap between the ends of the spring is a measure of the retraction capability of the spring. Max. gap is 250 mm. Note: If one spring needs to be renewed, the opposite spring must also be renewed.
179
Z cam brakes
RH brake adjuster - GREEN spring - RH pinion gear
LH thread
RH thread
Note: The tappet which locates against the primary shoe always has a LH thread.
LH brake adjuster - RED spring - LH pinion gear
180
Z cam brakes LH and RH components
Components that differ between LH and RH brake assemblies are: - tappet screw threads - adjuster pinion gear - adjuster spring
181
Z cam brakes 4 1
Templates for the setting tool: - hub reduction - 999 8522
3
- front wheel drive - 999 8525
2
- front axle with basic hub assembly, and axle with unit hubs - 999 8528
999 8386
182
Z cam brakes Initial setting of brake shoes
When new linings/shoes are fitted, initial setting of the shoes must be done using tool 999 8386. The tool has 2 main parts : 1 - shoe setting tool 2 - calibration tool with dial gauge (4). CAUTION Position of screw (3) is calibrated and locked in a position to represent a standard diameter brake drum. The position of this bolt must NEVER be altered.
Set tappet heads
Note: Before fitting the shoes, screw both tappet heads fully in, then unscrew one turn.
183
Z cam brakes
2
3
1
184
Z cam brakes Setting procedure
1 Fit 999 8386 in a vice, and ensure that sleeve (1) is securely tightened. 2 With the dial indicator wheel in contact with calibration screw (2), set the indicator to zero. 3 Ensuring that the dial indicator setting is not altered, remove the setting tool from the calibration tool.
Set trailing shoe first
4 Attach the setting tool to the hub, and turn the hub until indicator wheel (3) is in line with the second row of rivets at the abutment end of the trailing shoe. 5 Tap the shoe sideways until the indicator is at zero.
185
Z cam brakes 4
5
186
Z cam brakes
6 Turn the hub until the indicator wheel is in line with the second row of rivets at the expander end of the trailing shoe. 7 If the indicator is not at zero, turn the manual adjuster until the indicator is at zero. 8 Re-check the abutment end reading. Continue tapping the shoe and turning the adjuster until the indicator is at zero at both ends of the shoe.
Set leading shoe
9 Repeat the setting procedure on the leading shoe, starting at the abutment end, then moving to the adjuster end. If the indicator is not at zero at the adjuster end, remove cam housing cover (4) and cross-shaft (5).
187
Z cam brakes Set leading shoe - cont.
Note: If the cross-shaft is not removed, any adjustment of the leading shoe will alter the setting of the trailing shoe. Continue tapping the shoe and turning the adjuster until the indicator is at zero at both ends of the leading shoe. 10 Refit the cross-shaft - ensure correct tooth mesh - and cam housing cover.
188
Disc Brake 189
Disc brake
Info/illust reqʼd
190
191
192
