Checking Brake Proportioning Valve

Checking Brake Proportioning Valve

Use 2 brake pressure gages to check the brake proportioning valves that are attached to the master cylinder on non-antilock brake system (ABS) braking systems. These valves limit the outlet pressure to the rear brakes after a predetermined master cylinder pressure has been reached. On ABS braking systems, the hydraulic modulator/motor pack assembly controls the hydraulic pressure to both the rear wheel cylinders or rear calipers, and the front calipers.

When checking the brake proportioning valves, be sure that the hydraulic line pressure is measured simultaneously and diagonally on the front and the rear axles.

To measure the pressure, use the following steps.

1. Remove the bleeder valve and install a pressure gage to one of the rear brake cylinders.
2. Install another bleeder valve and install another pressure gage to the diagonally opposite front brake.
3. Build pressure by pressing firmly on the brake pedal several times. The pressure indicated on the gage is not regulated and represents the actual brake system hydraulic pressure.
4. Build pressure until the test values in the following proportioning valve test chart are achieved.

Important: If the pressure exceeds 10 000 kPa (1,450 psi), the pressure reading on the rear gage will not be accurate.


5. Remove the gages from the tested brake circuit and repeat the test on the remaining circuit.