Checking Brake Proportioning Valve
Use two brake pressure gauges to check brake proportioning valves that are attached to master cylinder on non-ABS braking systems. See Fig 1. These valves limit outlet pressure to rear brakes after a predetermined master cylinder pressure has been reached. (On ABS braking systems, hydraulic modulator/motor pack assembly controls hydraulic pressure to both rear wheel cylinders or rear calipers, and front calipers.).
When checking brake proportioning valves, be sure that hydraulic line pressure is measured simultaneously and diagonally on front and rear axles. To measure pressure, use following steps.
- Remove bleeder valve and install a pressure gauge to one of rear brake cylinders. Install another bleeder valve and install another pressure gauge to diagonally opposite front brake.
- Build pressure by pressing firmly on brake pedal several times. (The pressure indicated on gauge is not regulated and represents actual brake system hydraulic pressure.). Build pressure until test values in following proportioning valve test chart are achieved.