Genuine Audi 90 Brake Booster

Audi 90 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 90?

  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.
• Brake Booster
  4A0-612-107-A
  Q: How to remove and refit the Brake Booster servo unit on Audi 90?

  A:

  Take off the master cylinder and pull out the non-return valve and vacuum hose of the brake booster. Within the car, remove the brake booster pushrod cleavage of the brake pedal, the return spring, unhook it and remove the clip and cleavage pin. Unscrew the mounting nuts which hold the brake booster on the pedal bracket and bulkhead, and pull the brake booster out of the engine compartment. Take off the rubber O-ring of the unit and change it in case of need. Prior to refitting the brake booster, verify the pushrod dimension, as required, loosen the locknut, re-fit the clevis, and tighten the locknut. Refitting It is important to reverse the process when refitting but lubricate the clevis pin with a small amount of multi-purpose grease. Once this is completed, roll the rubber O-ring with the bulkhead to close the hole.