Power Brake Assist: Testing and Inspection

Fig. 1 Fabricated Brake Unit Adapter:

1. Use fabricated adapter, Fig. 1, connect vacuum gauge tool No. 201 589 13 21 00 or equivalent, to vacuum line between brake booster and check valve.
2. Connect Teves pressure tester tool No. 3 9305-1020.4 or equivalent, to brake caliper at vent screw, then bleed pressure tester.
3. Connect Bosch pedal force meter tool No. 0 681 148 EFSV 57 B or equivalent, to brake pedal.
4. Start and operate engine until 11-11.5 psi vacuum (.75-.8 bar) is present by accelerating, then quickly releasing accelerator pedal.
5. If low vacuum or decreasing vacuum is indicated, check the following:
a. Vacuum line leak.
b. Faulty check valve.
c. Faulty seal between booster and master cylinder.
d. Faulty brake unit control housing seal, if seal is faulty brake unit must be replaced.

Fig. 2 Power Brake Unit Test Specifications:

6. Measure line pressure at specified brake pedal force, Fig. 2.
7. If line pressure is ±140 psi (10 bar) from specifications, replace brake unit.
8. Remove test equipment, then bleed brake system at which pressure tester was connected.