Brake Proportioning/Combination Valve: Description and Operation

NOTE: Only vehicles without antilock brakes have proportioning valves. Vehicles with antilock brakes have electronic brake distribution that is built into the integrated control unit.

Proportioning valves balance front to rear braking by controlling the brake fluid hydraulic pressure to the rear brakes. Under light pedal application, the proportioning valve allows normal fluid flow to the rear brakes. Under higher pedal effort, the valve reduces fluid pressure to the rear brakes.
The non-antilock master cylinder is a four-outlet design with two screw-in proportioning valves attached directly to the master cylinder housing. One proportioning valve controls each rear brake.