Checking Brake Proportioning Valve

Use 2 brake pressure gages to check the brake proportioning valves that are attached to the master cylinder on non-ABS braking systems. These valves limit the outlet pressure to the rear brakes after a predetermined master cylinder pressure has been reached. On vehicles equipped with ABS, the hydraulic modulator assembly controls the hydraulic pressure to both the rear wheel cylinders 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 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 wheel cylinders.
2. At the diagonally opposite front brake caliper, remove the bleeder valve and install another pressure gage.
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.
IMPORTANT: If the pressure exceeds 10,000 kPa (1450 psi), the pressure reading on the rear gage will not be accurate.
4. Build pressure until the test values in the following proportioning valve test chart are achieved.
5. Remove the gages from the tested brake circuit.
NOTE: Refer to Fastener Notice in Cautions and Notices.
6. Reinstall the bleeder valves.

   Tighten:  Tighten the bleeder valves to 6 N.m (53 lb in).

7. Repeat the test on the remaining front/rear brake circuit.
8. Reinstall the bleeder valves.

   Tighten:  Tighten the bleeder valves to 6 N.m (53 lb in).