Proportioning Valve

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

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 slides first is determined, use the following procedure to diagnose the proportioning valve.
The test procedure for a premature rear wheel skid is the same for both rear wheel proportioning valves. After road testing vehicle to determine which wheel skids first, the proper test fittings required will have to be determined. Then follow the procedure below for testing the required proportioning valve.
1. Road test the vehicle. Determine which rear wheel exhibits premature rear wheel skid, then refer to the figure to determine which proportioning valve needs to be tested.
2. Remove hydraulic brake line from 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.

CAUTION: Be sure the pressure test fittings being installed into proportioning valve, have the correct thread sizes for installation into the proportioning valve and installation of rear brake line tube nut.






4. Install Pressure Test Fitting, Special Tool 8187 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.).






5. 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.).







6. 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. hose.






7. 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.
8. 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.
9. Install proportioning valve in rear brake line and hand tighten both tube nuts until they are fully seated in proportioning valve.
10. Tighten both brake line tube nuts at the proportioning valve to a torque of 17 Nm (145 inch lbs.).
11. Bleed the affected brake line. Refer to Brakes and Traction Control, Brakes, Brake Bleeding for procedures.