The proportioning valve is also known as a pressure differential warning valve.
Each of the brake circuits has a proportioning (relief) valve located inline between the rear wheels. The purpose of this valve is to ensure that brake pressure on all four wheels compensates for the change in weight distribution under varied braking conditions.
The harder the brakes are applied, the more weight there is on the front wheels. The valve regulates hydraulic pressure to the rear wheels, so that under hard braking conditions they receive a smaller percentage of the total braking effort. This prevents premature rear wheel lockup and possible skidding or loss of control.
- Disconnect the plug contact and screw out the warning switch so the pistons inside the valve may return to their normal position.
- Repair and bleed the faulty hydraulic circuit.
- Screw in the warning switch and tighten it to 10-14 ft. lbs. (14-19 Nm).
- Connect the plug contact.
REMOVAL & INSTALLATION
- Place a rag under the valve to catch the brake fluid.
- Detach the electrical connector from the switch and slacken the brake pipe connections.
- Unfasten the bolt(s) which retain the valve to the underbody and unscrew the brake pipe connections.
- Remove the differential warning valve.
- Place a new seal on it, then screw the valve onto the rear brake hose and hand-tighten.
- Secure the valve to the underbody with the retaining bolt(s).
- Connect the brake pipe and tighten both connections, making sure there is no tension on the flexible rear hose.
- Bleed the brake system.