Proportioning Valve

NOTE: The following procedure is for the diagnosis and testing of the proportioning valve(s) on a vehicle equipped with ABS. For diagnosis and testing of proportioning valves on a vehicle without ABS, Refer to Brakes, Testing and Inspection, Procedures.

If a condition of premature rear wheel skid occurs on a vehicle, the proportioning valve should always be tested prior to it being replaced. This is due to the fact that there are conditions other then a faulty proportioning valve which can cause a premature rear wheel skid.






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 slides first is essential. Once the wheel which is skidding first is determined, use the following procedure to diagnose the proportioning valve.
The test procedure is the same for both rear wheel proportioning valves. After road testing vehicle to determine which wheel skids first, follow the procedure below for testing the required proportioning valve.






1. Remove the cover securing the chassis brake tubes and the fuel lines to the vehicle floor pan.
2. Remove the chassis brake tubes from the proportioning valve controlling the rear wheel of the vehicle which has premature wheel skid.
3. Remove the proportioning valve from the rear brake chassis tube.
4. Remove the routing clips for the chassis brake tubes and fuel lines from the floor pan.

CAUTION: The chassis brake tube must be removed from the routing clips. This is to prevent the chassis brake tube from having to be bent when installing the proportioning valve with the pressure test fittings.

5. Remove the chassis brake tube that requires testing of its proportioning valve from the routing clips.

CAUTION: Be sure the pressure test fittings being installed into the proportioning valve have the correct thread sizes and flares for installation into the proportioning valve and for installation of the chassis brake tubes.






6. Install Pressure Test Fitting, Special Tool 6833-1 in the inlet port of the proportioning valve. Install Pressure Test Fitting, Special Tool 8187-2 in the outlet port of the proportioning valve. Tighten tube nuts to a torque of 17 Nm (145 inch lbs.).






7. Install the proportioning valve with the pressure test fittings installed, in the chassis brake tube. Tighten both tube nuts to a torque of 17 Nm (145 inch lbs.).






8. Install a Pressure Gauge, Special Tool C-4007-A into each pressure test fitting. Bleed air out of hose from pressure test fitting to pressure gauge, at pressure gauge to remove all trapped air.






9. With the aid of a helper, apply pressure to the brake pedal until reading on proportioning valve inlet gauge, is at the pressure shown on the following chart, PROPORTIONING VALVE APPLICATIONS AND PRESSURE SPECIFICATIONS. Then check the pressure reading on the proportioning valve outlet gauge. If proportioning valve outlet pressure does not agree with value shown on the following chart, when inlet pressure shown on chart is obtained, replace the proportioning valve. If proportioning valve is within pressure specifications do not replace proportioning valve.
10. Check rear wheel brake shoe linings for contamination or for replacement brake shoes not meeting OEM brake lining material specifications. These conditions can also be a possible cause for a premature rear wheel skid.
11. Install proportioning valve on end of brake flex hose. Tighten the proportioning valve to a torque of 17 Nm (145 inch lbs.).
12. Install brake tube on proportioning valve. Torque tube nut to 17 Nm (145 inch lbs.) torque.
13. Bleed the affected brake line. Refer to Brakes and Traction Control, Brakes, Brake Bleeding Service and Repair for procedures.