Audi 80 Quiz
Brake System

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

Disc brake assemblies do not have a self-energizing effect like drum brakes, so a considerably higher braking force is required. For this reason, the Audi 80 is equipped with a pneumatic brake booster that adds approximately 60% of the braking force. Nevertheless, the brake pedal is directly connected to the brake piston in the master brake cylinder, so braking is still possible if the booster fails. However, the pedal pressure required in this case must be increased several times.


Additional force is provided by reduced pressure from the intake manifold. The brake booster is connected by a hose to the intake manifold. When braking, the pressure difference between the outside air pressure and the reduced pressure in the intake manifold moves the large flexible diaphragm and additionally presses on the piston in the master brake cylinder. If the engine is not running, the booster cannot develop any additional braking force. If the engine suddenly stalls, a small reserve remains for a few brake applications; after that, only leg force is available.


Vacuum Pump
To improve brake force retention, the 5-cylinder engine is equipped with an additional vacuum pump mounted on the left side of the cylinder head and driven by the camshaft. It increases the reduced pressure in the hoses to the brake booster.

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