Overview - Brake Booster/Brake Master Cylinder

Tip:

• Always replace the self-locking nuts and bolts.
• Replace damaged bolts and nuts.
• Clean the bolts and nuts before reusing.

Fig 1: Exploded View Of Brake Booster/Brake Master Cylinder

Courtesy of AUDI OF AMERICA, LLC

1. Brake Line
   • 16 Nm
   • Brake master cylinder/secondary piston circuit to hydraulic unit
     CAUTION:

     Risk of destroying the brake lines by bending.

     - Never change the shape of the brake lines.

     - A damaged or bent brake line must be replaced.

2. Master Brake Cylinder
   • Replace completely if faulty
   • Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING 

     Tip:

     • Always replace the gasket between the master brake cylinder and the brake booster.
3. Bolt
   • 25 Nm
4. Nut
   • 49 Nm
   • Always replace after removing
5. Plugs
   • To install, coat with brake fluid
6. Bolt
   • 8 Nm
     • Replace if damaged
     • The locking bolt must go through the brake fluid reservoir tabs.
     • The locking bolt must go through the brake master cylinder.
     • The locking bolt must be tightened.
7. Brake Fluid Reservoir
   • The locking bolt must go through the brake fluid reservoir tabs.
   • The locking bolt must go through the brake master cylinder.
   • The locking bolt must be tightened.
   • Refer to BRAKE FLUID RESERVOIR, REMOVING AND INSTALLING 
8. Seal
   • Cannot be replaced as a separate part
9. Cap
   • With seal
10. Rubber Buffer
11. Protective Plate
    • Not installed on all models
12. Rubber Buffer
13. Bolt
    • 8 Nm
14. Brake Fluid Level Warning Switch -F34-
    • Refer to Brake Fluid Level Warning Switch -F34-, REMOVING AND INSTALLING 
15. Seal
    • Replace after removing.
16. Brake Booster
    • Function Test:

      -- With the engine switched off, press the brake pedal firmly several times (to reduce the vacuum in the device).

      -- Hold the brake pedal with average foot pressure and start the engine. If the brake booster is working properly, the brake pedal will be felt to give noticeably under foot (booster becomes effective).

    • Refer to BRAKE BOOSTER, REMOVING AND INSTALLING 
    • Adjust the ball head. Refer to Fig 2.
    • Always replace the seal between the bulkhead and the brake booster
    • Remove all sealant residue from the bulkhead and brake booster.

      Tip:

      • Always replace the gasket between the master brake cylinder and the brake booster.
17. Seal
    • Always replace after removing
18. Primary piston
    • The primary piston is only loosely inserted into the brake master cylinder and can fall into the brake booster when removing
19. Brake Pedal Position Sensor -G100- Actuator Rod
    • Must not fall in the brake booster when removing the brake master cylinder.
    • Must remain inserted when installing the brake master cylinder
    • Refer to NOTE ABOUT Brake Pedal Position Sensor -G100- ACTUATOR ROD 
20. Brake Pedal Position Sensor -G100-
    • Brake Lamp Switch
    • Refer to Brake Pedal Position Sensor -G100-, REMOVING AND INSTALLING
      • Make sure the installation position of the Brake Pedal Position Sensor -G100- is correct.
      • After each removal and installation, the Brake Pedal Position Sensor -G100- must be recalibrated.
      • To do this, go into "Guided Functions  , Basic Setting, Brake Pedal Position Sensor G100".
21. Bolt
    • 8 Nm
    • The Brake Pedal Position Sensor -G100- must be flush with the outer edge of the mount
22. Brake Line
    • 16 Nm
    • Brake master cylinder/primary piston circuit to hydraulic unit
      CAUTION:

      Risk of destroying the brake lines by bending.

      - Never change the shape of the brake lines.

      - A damaged or bent brake line must be replaced.

Adjusting the Brake Booster Ball Head

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI OF AMERICA, LLC

• Dimension -a- = 167.2 mm ± 0.5 mm

• When measuring, the ball head must be aligned at a right angle to the brake booster surface.
• Measure to end of ball head without the seal.

Tightening Specification