ABS Description and Operation

When conventional brakes are applied in an emergency stop or on ice, one or more wheels may lock. This may result in loss of steering control and vehicle stability. The purpose of the Bendix Antilock-10 Brake system is to prevent wheel lockup under heavy braking conditions. The system offers the driver increased safety and control during braking. Antilock braking operates only at speeds above three miles per hour.

During normal braking the Controller - Antilock Brake (CAB) monitors the brake system, but does not control brake system operation. Fluid passes freely through the single unit master cylinder/hydraulic booster/modulator assembly to all brakes.

If a wheel locking tendency is sensed during a brake application, the system will enter antilock mode. During antilock braking, hydraulic pressure in the four wheel circuits is modulated to prevent any wheel from locking.

A wheel speed sensor (WSS) is located at each wheel to determine when antilock braking is required. The sensor sends wheel speed information to the CAB. If a sensor detects a wheel locking tendency at any wheel, the CAB signals the pressure modulator to modulate brake pressure.

Electrical valves control modulation. These are the isolation, build, and decay (reduce) valves. The front wheels each have these three valves and are controlled separately. The rear wheels have separate isolation valves, but for stability share one build valve and one decay valve.

The system can isolate, build, or decay pressure at each wheel, depending on the signals generated by the wheel speed sensor at each wheel and received at the CAB. The brake at each wheel where a wheel locking tendency is sensed is then modulated up to 15 times per second until the antilock incident is over.

Under normal braking conditions, the Bendix Antilock-10 functions with a diagonally split master cylinder much the same as a standard brake system. Antilock braking is different from conventional braking in that power assist is provided by hydraulic power instead of the conventional vacuum assist. As a result, there are several performance characteristics that may seem different from conventional braking, but should be considered normal for antilock braking. These are described below.

- In general, pedal feel during braking will be similar to that of a conventional vacuum-boosted brake system. If antilock operation occurs during hard braking, some pulsations may be felt in the brake pedal. These pulsations are caused by the isolation, building, and decaying of brake fluid pressure within the brake lines and master cylinder.

- Although the Bendix Antilock-10 system prevents complete wheel lock-up, some wheel slip is required for the best braking performance. This slip may result in some tire chirping, depending on the road surface.

^ This sound should not be interpreted as total wheel lock-up (although wheel lock-up may occur at the end of an antilock stop below 3 MPH).

^ Complete wheel lock-up normally leaves black tire marks on dry pavement, while antilock braking may leave only light patched marks.