Proportioning Valve

PROPORTIONING VALVE TEST (WITH AND WITHOUT ANTILOCK BRAKES)

CAUTION: Not all components use the same type tubing flare. The tube leading into the proportioning valve has an ISO flare, while the flex hose coming out of the proportioning valve has a standard double-inverted flare. Use the correct adapters when installing gauges to test proportioning valves.

Both vehicles, with Antilock Brakes, and without Antilock Brakes, have two proportioning valves. One valve is connected to each rear flex hose. One proportioning valve controls the right rear brake, and the other proportioning valve controls the left rear brake.
On vehicles without ABS, if premature wheel skid occurs on a hard brake application, it could be an indication that a malfunction has occurred with one of the two rear brake proportioning valves. Test the valve that controls the side of the vehicle on which the skid occurs.
On vehicles with ABS, if premature rear wheel ABS cycling occurs on a hard brake application, it could be an indication that a malfunction has occurred with one of the two proportioning valves. Since ABS cycles both rear brakes together, both valves must be tested to isolate the suspect proportioning valve.
1. Raise the vehicle on jack stands or centered on a hoist.
2. Clean any debris away from the suspect proportioning valve, connections, and area.






3. Remove the chassis brake tube from the suspect proportioning valve.
4. Remove the proportioning valve from the rear flex hose which is held stationary by a bracket mounted on the back side of the crossmember.






5. Remove the retainer clip securing the rear flex hose from its bracket. This should be done to allow the proportioning valve pressure test fittings to be installed without bending the chassis brake tube.

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

6. Correctly install Pressure Test Fittings, Special Tool 6892-2 into the inlet port, and Special Tool 8187-2 into the outlet port, of the proportioning valve.
7. Install the proportioning valve and the Pressure Test Fittings, Special Tool 6892-2 and 8187-2, as an assembly back into the chassis brake tube. Connect Special Tool 6892-2 to the chassis brake tube, and Special Tool 8187-2 to the brake flex hose.







8. Install a Pressure Gauge, Special Tool C-4007-A into each pressure test fitting. Bleed any air out of the system. This includes bleeding the air from the hose between the pressure test fitting and pressure gauge, which is done at the pressure gauge.
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 chart. 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. Remove the pressure gauges from the pressure test fittings.
11. Remove the proportioning valve and the Pressure Test Fittings, Special Tool 6892-2, and 8187-2 from the chassis brake tube and rear flex hose. Remove the pressure test fittings from the proportioning valve.
12. Install the rear brake flex hose to its mounting bracket using a new retainer clip.
13. Install the proportioning valve to the rear brake flex hose. Tighten to a torque of 17 Nm (145 inch lbs.).
14. Install the chassis brake tube to the proportioning valve. Tighten the tube nut to a torque of 17 Nm (145 inch lbs.).
15. Bleed the affected brake line.
16. On vehicles with Antilock Brakes, repeat the above steps for the other proportioning valve.
17. If no problem is found with the proportioning valves, check the 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.





PROPORTIONING VALVE APPLICATIONS AND PRESSURE SPECIFICATIONS