Proportioning Valve: Notes

NOTE: Only vehicles without antilock brakes have proportioning valves. Vehicles with antilock brakes have Electronic Variable Brake Proportioning (EVBP) which is built into the ABS Integrated Control Unit (ICU).

Fig 1: Proportioning Valves

Courtesy of DAIMLERCHRYSLER CORP.

1 - PROPORTIONING VALVE IN SECONDARY PORT

2 - MASTER CYLINDER

3 - PROPORTIONING VALVE IN PRIMARY PORT

If premature rear wheel skid occurs on a hard brake application, it could be an indication that a malfunction has occurred with one of the proportioning valves (1, 3).

One proportioning valve controls the right rear brake and the other proportioning valve controls the left rear brake. Therefore, a road test to determine which rear brake skids first is essential.

Before testing the proportioning valve in question, inspect the rear brake linings for contamination or for replacement shoes not meeting the OEM brake lining material specifications.

The proportioning valve should always be tested prior to being replaced.

The in-line proportioning valves used on this vehicle require special pressure fittings to test the proportioning valves for proper proportioning valve function. The pressure fittings are installed before and after the proportioning valve being tested to verify proportioning valve is maintaining the required hydraulic pressure to the rear wheel brake which it controls.