Brake Proportioning/Combination Valve: Testing and Inspection

DIAGNOSIS AND TESTING - PROPORTIONING VALVE
Both vehicles with Antilock Brakes and without Antilock Brakes have two proportioning valves. One proportioning valve controls the right rear brake, and the other proportioning valve controls the left rear brake. ABS and early production non-ABS applications have valves that are connected to each rear flex hose. Later production non-ABS applications have proportioning valves located in the junction block.
Although valve locations may differ, the valves have the same pressure specifications and are tested in the same way using Pressure Gauge, Special Tool C-4007-A with different adapters. Refer to the proper proportioning valve test below depending on application.
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.

PROPORTIONING VALVE TEST (ABS AND EARLY PRODUCTION NON-ABS APPLICATIONS)

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.

1. Raise the vehicle.
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 at the end of this procedure. 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 (once inlet pressure shown on chart is obtained), replace the proportioning valve. If pressure is within 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 cause premature rear wheel skid.

PROPORTIONING VALVE TEST (LATER PRODUCTION NON-ABS APPLICATIONS)
1. If the left rear proportioning valve is suspect, disconnect the tube nut fitting at the master cylinder primary port (port closest to power brake booster). Install Adapter, Special Tool 8494-2, in its place on the master cylinder.
2. If the right rear proportioning valve is suspect, disconnect the tube nut fitting at the master cylinder secondary port (port furthest from power brake booster). Install Adapter, Special Tool 8494-1, in its place on the master cylinder.
3. Connect primary brake tube to Adapter.
4. Install a Pressure Gauge, Special Tool C-4007-A, to the Adapter.
5. Tighten all tube nut fittings to 17 Nm (145 inch lbs.) torque.





6. Remove screw fastening the speed control servo to the upper radiator closure panel.
7. Remove screw fastening the washer filler tube to the upper radiator closure panel.





8. Remove nut and screw securing transmission control module to vehicle.
9. Lift the transmission control module (with speed control servo attached) from its mount leaving its wiring harness attached. Move it off to the side toward the engine making sure not to strain the wires and speed control servo cable.
10. Clean any debris away from the fittings on top of the junction block.





11. Using the following figure, remove the chassis brake tube leading to either the left rear or right rear brake at the junction block.
12. If the left rear proportioning valve is suspect, install Adapter, Special Tool 8494-3, in its place on the junction block.
13. If the right rear proportioning valve is suspect, install Adapter, Special Tool 8494-4, in its place on the junction block.
14. Install a Pressure Gauge, Special Tool C-4007-A, to the Adapter.
15. Tighten all tube nut fittings to 17 Nm (145 inch lbs.) torque.
16. 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.
17. With the aid of a helper, apply pressure to the brake pedal until reading on proportioning valve inlet gauge (at master cylinder) is at the pressure shown on the chart at the end of this procedure. Then check the pressure reading on the proportioning valve outlet gauge (at junction block outlet to rear brake). If proportioning valve outlet pressure does not agree with value shown on the chart (once inlet pressure shown on chart is obtained), replace the junction block (with internal proportioning valves). If pressure is within specifications, do not replace proportioning valve and perform the following steps.
18. Remove the Pressure Gauge and Adapter, Special Tool 8494-3 or 8494-4, from junction block.
19. Reinstall the chassis brake tube to the junction block port. Tighten tube nut fitting to 17 Nm (145 inch lbs.) torque.
20. Install the transmission control module (with speed control servo attached) in its normal position. Install the nut and screw securing it in place.
21. Install the transmission control module mounting nut and screw securing it in place. Tighten the screw to 6 Nm (45 inch lbs.). Tighten the nut to 12 Nm (107 inch lbs.) torque.
22. Install the screw attaching the washer filler tube to the upper radiator closure panel.
23. Install the screw attaching the speed control servo to the upper radiator closure panel.
24. Remove the Pressure Gauge and Adapter, Special Tool 8494-1 or 8494-2, from master cylinder.
25. Install the brake tube to the master cylinder primary or secondary port. Tighten the tube nut to a torque of 17 Nm (145 inch lbs.).
26. Bleed the affected brake line.
27. 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 cause premature rear wheel skid.





PROPORTIONING VALVE APPLICATIONS AND PRESSURE SPECIFICATIONS