Brake System

Page 32

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Volvo Bus Service and Maintenance Manual

 Automatic slack adjusters
58 Check travel for the automatic slack adjusters and also the anchor bolt mounting.
 Anti-lock brakes (ABS)
59 Check during test driving that the system's function-check lamp lights when the starting key (switch) is switched to Drive and goes out at approx. 7-8 km/h.

Automatic slack adjusters, travel in mm

NOTE! When checking the travel, also check-tighten the anchor bolts and check for damage.
Front wheels30-4035-4535-4530-4025-35
Rear wheels35-4530-4030-40135-4530-401
Articulated wheels
Articulated wheels
1 The fig on previous page is for lever length of 133 to 152 mm. For lever lengths of 165 mm the travel is 35-45 mm.

All the above values apply to automatic slack adjusters with S-cam wheel brakes. Other instructions apply concerning automatic adjustment of wedge brakes or Z-cam brakes.

Note: Using a brake tester is the simplest way to check the brake power, for binding, pulsation, smoothness, brake application and release. The brake power is assessed when the amount of force used on the brake pedal and in comparison to another bus of the same type.

For a wheel brake on an axle with a load-sensing valve Wabco 475 711..., the brake power for a 2-axle bus is reduced by 25% and with a non-steered trailing unit 20%. For buses with Wabco 475 700... the brake power is reduced by 30% for the axle on which a load-sensing valve is mounted.

Anti-lock brakes

In the event of system voltage feed failure or a fault in the electronic control unit, the function-check lamp will continue to light at speeds above 7-8 km/h. The system is diagonally connected so that, if one of the circuits fail, the ABS-system automatically cuts out this circuit.

At the same moment the starting key (switch) is turned (applies to starting engine with early type ABS-system), the ABS-system control valves perform a self-check by emitting a chattering sound that indicates that they do not bind. Each control valve must be listened to separately.

This means that the starting key (switch) must be switched on and off for each and every one of the control valves.

ABS control valves

If the control valves are not binding, their movement can be felt on the outside.

The inductive sender on the inside of each wheel is held in position by a spring retainer. Max. permitted distance between the inductive sender and the toothed gear is 0.3 mm. The distance is adjusted by manually pressing the inductive sender towards the toothed gear. The correct distance sets automatically when the gear starts to rotate. Tightening torque for the sensor retainer tensioning band is 20 Nm (2 kgf m).

ABS inductive sender