Brake Proportioning/Combination Valve: Testing and Inspection

NOTE: A vehicle that is equipped as a Transitional Low Emission Vehicle (TLEV) having two front catalytic converters, uses unique proportioning valve applications. Refer to the test procedures below to determine which should be used if testing a proportioning valve on a TLEV equipped vehicle.

GENERAL INFORMATION
If premature rear wheel skid occurs on hard brake application, it could be an indication that a malfunction has occurred with the proportioning valve unit. The proportioning valve is designed with two separate systems. One half controls the right rear brake, and the other half controls the left rear brake. Therefore, a road test to determine which rear brake slides first is essential.

CAUTION: All brake line fittings used on this vehicle use ISO style tubing flares. Ensure that when fabricating adapter tubes required to test proportioning valve operation. That only ISO style tubing flares are used at proportioning valve connections. Failure to use ISO style tubing flares at the proportioning valve connections, will destroy the tubing seats in the proportioning valve.

Tube Connection For Right Rear Skidding:

RIGHT REAR WHEEL SLIDES FIRST
To test the proportioning valve when the right rear wheel slides first, leave the front brakes connected to the valve, and proceed as follows:

1. Install one gauge and (TEE) of set C-4007-A, or equivalent between the brake line from the master cylinder secondary port and the brake valve assembly.
2. Install the second gauge of set C-4007-A, or equivalent to the right rear brake outlet port. Gauge to be attached using an adapter tube, made from a short piece of brake tube and (1) 3/8 x 24 tube nut, and (1) M1Ox1 tube nut. Connect the hose to the valve. Bleed the hose and gauge.
3. Have a helper exert pressure on the brake pedal (holding pressure) to get a reading on the valve inlet gauge and check the reading on the outlet gauge. If the inlet and outlet pressures do not agree with the values on the following chart, replace the valve.

Tube Connection For Left Rear Skidding:

LEFT REAR WHEEL SLIDES FIRST
To test the proportioning valve when the left rear wheel slides first, leave the front brakes connected to the valve, and proceed as follows:

1. Install one gauge and (TEE) of set C-4007-A, or equivalent between brake line from master cylinder primary port and brake valve assembly.
2. Install the second gauge of set C-4007-A, or equivalent to the left rear brake outlet port. An adapter tube, made up from a M12x1 tube nut, a short piece of brake tube and 3/8 x 24 tube nut, will be required to connect hose to valve. Bleed the gauge and hose.
3. Have a helper exert pressure on the brake pedal. Hold pressure steady to get a reading on the valve inlet gauge and check the reading on the outlet gauge. If the inlet and outlet pressures do not agree with the values on the following chart, replace the valve.