Service manual

Group 59 Anti-Lock Brake System (Bendix) Design and Function

Design and Function

System Description

The Bendix Anti-Lock Braking System (ABS) is an elec-

tronically controlled system that continually monitors

wheel speed and controls wheel braking during extreme

braking situations, such as during hard braking or

slippery road conditions. The ABS is an important com-

ponent of the foundation brake system and works in

conjunction with the standard vehicle braking system. It

improves the vehicle’s stability and control by reducing

wheel lock during braking.

The ABS electronically monitors the rotational speed of

both front wheels and the wheels on the rear axle (for-

ward rear axle on tandem conﬁgurations). The wheel

rotation signals are sent to an Electronic Control Unit

(ECU) which sends signals to the ABS modulator valves

if it detects that a wheel has locked up or is about to lock

up. The modulator valves control the pressure in the

brake assembly air chambers.

Wheel rotation is determined by an electronic sensor

mounted in the brake spider. A signal is generated by

the sensor as high spots on a tooth wheel pass by the

sensor. The tooth wheel is either mounted on or is part

of the wheel hub.

W5000936

Note: Vehicle with spring suspension shown. Vehicle with air suspension has sensors on the rear axle.