With Antilock Brakes

CAUTION: Proportioning valves should never be disassembled.

Proportioning Valve:

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.

Proportioning Valve Location In Vehicle:

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.


PROPORTIONING VALVE TEST
The test procedure is the same for both rear proportioning valves. After road testing the vehicle to determine which wheel skids first, follow the procedure below for testing the suspect proportioning valve.

Brake Pedal Holding Tool:

1. Using a brake pedal holding tool as shown, depress the brake pedal past its first one inch of travel and hold it in this position. This will isolate the master cylinder from the brake hydraulic system and will not allow the brake fluid to drain out of the master cylinder reservoir.
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 brake flex hose routing bracket from the frame to allow enough room for the pressure test equipment to be installed.

Pressure Test Fittings Installed On Proportioning Valve:

4. 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 (146 inch lbs.).

Proportioning Valve With Pressure Test Fittings Installed:

5. Reinstall the proportioning valve with the pressure test fittings attached in the vehicle. Attach Pressure Test Fitting, Special Tool 8187-2, to the chassis brake tube leading to the rear brake. Attach Pressure Test Fitting, Special Tool 6833-1, to the chassis brake tube coming from the HCU. Tighten the tube nuts to a torque of 17 Nm (145 inch lbs.).

Pressure Gauges Installed On Pressure Test Fittings:

6. Install a Pressure Gauge, Special Tool C-4007-A, into each pressure test fitting.
7. Remove the brake pedal holding tool from the brake pedal and bleed any air out of the gauge hoses at the pressure gauge.

Brake Proportioning Valve Applications And Pressure Specifications:

8. With the aid of a helper, apply pressure to the brake pedal until the reading on proportioning valve inlet gauge is at the inlet pressure in the BRAKE PROPORTIONING VALVE APPLICATIONS AND PRESSURE SPECIFICATIONS table following this procedure. Once inlet pressure has been achieved, check the pressure reading on the proportioning valve outlet gauge. If the proportioning valve outlet pressure does not agree with value in the table, replace the proportioning valve. If proportioning valve is within pressure specifications, the valve is good and does not require replacement.
9. Reinstall the brake holding tool on the brake pedal and remove the test equipment from the vehicle.
10. Install proportioning valve in chassis brake tube. Tighten the proportioning valve tube nuts to a torque of 17 Nm (145 inch lbs.).
11. Reattach the brake flex hose routing bracket to the frame.
12. Bleed the affected brake line. See Brake Bleeding.