ABS General System Description

Fig. 1 - Anti-lock Brake System Components:

The Delco-Moraine anti-lock brake system (DM ABS-III), Fig. 1, is designed to reduce the tendency of a wheel to lose traction (lock), while braking. In most instances, the base power brake system operates. Anti-lock braking occurs only when a combination of wheel speed sensors and a microprocessor determine a wheel is about to loose traction during braking. The DM ABS-III then adjusts brake pressure to both front wheels and/or both rear wheels to reduce the tendency of the wheels to lock-up. This system helps the driver maintain steering during braking, over a variety of road surfaces.

During ABS operation, the Delco-Moraine ABS-III system cycles (pulses), the brakes, adjusting line pressures, to obtain optimum stopping distance and vehicle control. During this cycling, the brake pedal will pulsate and clicking noises will be heard from the solenoids as they control the cycling. Clicking of the solenoids and pulsating of the brake pedal at this time and during a short period after vehicle starting is normal.
During ABS braking, to optimize stopping distance, the ABS will pump the brake pedal. The driver should press steadily and firmly on the brake pedal. The driver should never pump the brake pedal when ABS is activated.
During ABS operation, some tire noise may be heard. This noise is normal and results from slippage of the tire on the road surface. The amount of tire slippage will depend upon road and tire conditions. A tire will also seem to lock momentarily. This is a result of rapid changes in wheel speed and is also normal. A wheel that locks and stays locked for more than one second is not normal and should be serviced immediately.