Principles of Operation

Vehicles equipped with anti-lock brake system (ABS) and ABS/traction control do not use a proportioning valve. Hydraulic pressure to the brake assemblies is controlled by the hydraulic control unit (HCU) as directed by the electronic control unit (ECU). Non-ABS systems are equipped with a junction block in the engine compartment and a brake load sensing-proportioning valve in the rear. During braking, weight is shifted to the front of the vehicle, causing the rear to rise. The brake load sensing-proportioning valve is mounted on the body and is attached to the rear suspension lower control arm. As the body and suspension separate, the valve proportions pressure to the rear wheels to prevent premature rear brake lockup.