Genuine Audi 80 Brake Booster

Audi 80 Brake Booster Parts and Q&A

• Pressure Metering Valve
  443-614-151-H
  Q: What is the function and operation of the Brake Booster vacuum servo unit in brake systems on Audi 80?

  A:

  The brake booster, positioned between the brake pedal and the master cylinder, assists the driver when the brake pedal is pressed, drawing vacuum from the inlet manifold except in 1994 cc automatic transmission models, which utilize a Vacuum Pump on the cylinder head operated by a plunger in contact with the camshaft. In 1781 cc automatic transmission models, a vacuum booster is included in the hose connecting the inlet manifold to the brake booster. The unit consists of a diaphragm and non-return valve; when the brake pedal is released, vacuum is applied to both sides of the diaphragm, but when pressed, one side opens to the atmosphere, creating unequal pressures that help depress the master cylinder pistons. While the brake booster is generally reliable, it should be replaced if faulty, as a failure does not affect the hydraulic system, though higher pedal pressures will be required. To test the unit, the brake pedal should be depressed several times with the engine off to release the vacuum, then moderate pressure should be applied before starting the engine, with a slight downward movement of the pedal indicating proper operation.