Vacuum Brake Booster Check Valve: Testing and Inspection

CHECK VALVE OPERATION CHECK

1. Remove the check valve.

CAUTION
Replace the check valve when it is faulty.





2. Using a vacuum pump, check operation of the check valve.





PROPORTIONING VALVE FUNCTION TEST [VEHICLES WITHOUT ABS]

CAUTION
The proportioning valves are installed independently for the right and left brake lines. Always measure each valve.





1. Connect two pressure gauges to the output port of the master cylinder and output port of the proportioning valve.
2. Bleed the brake line and the pressure gauges.





3. Depress the brake pedal gradually. Then check that the split point, where the output fluid pressure begins to drop in proportion to the output fluid pressure, is at the standard value.

Standard value:
2.21 - 2.70 MPa (320 - 391 psi) [Vehicles with rear drum brake]
1.81 - 2.21 MPa (262 - 320 psi) [Vehicles with rear disc brake]

4. Depress the brake pedal more strongly than at the above step. Then check that the output fluid pressure is at the standard value when the input fluid pressure is 6.86 MPa (996 psi).

Standard value:
3.29 - 3.82 MPa (477 - 554 psi) [Vehicles with rear drum brake]
2.33 - 3.46 MPa (338 - 501 psi) [Vehicles with rear disc brake]

5. Measure each output fluid pressure at both valves, and check that the difference between the two is at the limit value or less.

Limit: 0.5 MPa (73 psi)

6. If the measured pressure exceeds the limit, replace the proportioning valve.