The Anti-lock Brake System (ABS) functions by releasing and applying fluid pressure to either the front disc brake calipers or the rear drum brake wheel cylinders during certain braking conditions. The ABS only actuates when one or more wheels approach a slip condition. The ABS automatically senses the slip and activates the fluid pressure control function.
The anti-lock actuator assembly is not used under normal braking conditions. Under normal conditions, fluid from the master cylinder enters the two inlet ports located on top of the actuator assembly. The fluid then flows through the normally open solenoid valves to each respective wheel location.
The anti-lock wheel speed sensors operate on the magnetic induction principle. As the teeth on the sensor indicator rotate past the stationary sensor, a signal proportional to the speed of rotation is generated and sent via a cable to the control module. The front sensors are attached to the wheel knuckles and the sensor indicators are pressed onto the outer ends of the halfshaft. The rear wheel sensors are attached to the brake backing plate and the sensor indicators are pressed onto the inner hubs of the drums.
The anti-lock relay is actuated by the control module. The relay is grounded by the control module to power up the system. The control module consists of the fail-safe and motor relays. The fail-safe relay inhibits solenoid operation and turns the anti-lock brake warning indicator on and off. The motor relay controls pump and motor operation.
The ABS system is operated and monitored by a control module. The module receives readings from the two rear and two front wheel speed sensors and uses this information to compare wheel speeds. Once the control module senses wheel lock-up under a severe braking condition, it signals the anti-lock actuator assembly, which closes the flow control valve of the affected circuit. This regulates the fluid entering the circuit, thus preventing wheel lock-up. When the control module senses that the wheel is decelerating, it sends a signal to open the flow control valve, thus reducing any pressure between the control valve and the affected brake actuator. The fluid is then returned to the master cylinder.