Audi 80 Quiz
Brake System

Checking the Brake Booster

In this manual: Brake System
Technical Description — 39Engines — 41Exhaust System — 13Cooling System — 28Fuel tank and fuel pump — 12Air Filter and Intake Ducts — 13Mono-Motronic Injection System — 18Digifant Injection System — 19KE-III-Jetronic Injection System — 35MPI and MPFI Injection Systems — 32Clutch — 11Transmission and Driveline — 21Suspension and Steering — 33Brake System — 41Anti-lock brake system — 8Wheels and Tires — 13Body Electrical System — 35Ignition System — 24Lighting — 14Signaling Devices — 7Instruments and Auxiliary Equipment — 54Heating and Ventilation — 7Body Components — 18Troubleshooting — 6Specifications — 13
~1min read

The engine must be switched off.

Depress the brake pedal 10 times.

Keep the brake pedal fully depressed and start the engine.

If the brake booster is working properly, the pedal should move slightly down at this moment. If this does not happen, the brake booster is faulty.

The fault is most likely in the vacuum system: a leaking vacuum hose from the intake manifold to the brake booster, a faulty check valve in the vacuum hose near the booster, a faulty rubber seal between the master brake cylinder and the booster, or a faulty booster diaphragm.

To check the check valve, disconnect the vacuum hose from the brake booster.

Air should be able to flow out, but not be drawn in.

The check valve is only available together with the corresponding vacuum hose.

To replace a damaged rubber seal between the master brake cylinder and the booster, the cylinder must be removed.

A faulty brake booster cannot be repaired. Replace.

Test yourself

A quick Audi 80 quiz: every answer comes with an explanation and a link to the manual page.