Overview - Brake Booster/Brake Master Cylinder, Vacuum Brake Booster

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
2. Brake Master Cylinder
   • Replace completely if faulty
   • Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING, WITH VACUUM BRAKE MASTER CYLINDER 
3. Bolt
   • 25 Nm
     CAUTION:

     Clean the bolts and nuts before reusing.

     Replace the bolts and nuts if damaged.

     Replace the self-locking bolts and nuts after removing

4. Nut
   • 55 Nm
   • Replace after removing.
     CAUTION:

     Clean the bolts and nuts before reusing.

     Replace the bolts and nuts if damaged.

     Replace the self-locking bolts and nuts after removing

5. Plugs
   • To install, coat with brake fluid
6. Locking Pin
   • 8 Nm
     • The locking pin must go through the brake fluid reservoir tabs.
     • The locking pin must go through the brake master cylinder.
     • The locking pin must be tightened.
7. Brake Fluid Reservoir
   • Fill pressure maximum 6 bar.
     • The locking pin must go through the brake fluid reservoir tabs.
     • The locking pin must go through the brake master cylinder.
     • The locking pin must be tightened.
   • Refer to BRAKE FLUID RESERVOIR, REMOVING AND INSTALLING 
8. Seal
   • Replace if damaged
9. Cap
10. Rubber Buffer
11. Protective Plate
    • Equipped on some models
      CAUTION:

      The protective plate is only installed depending on the model.

12. Rubber Buffer
13. Bolt
    • 8 Nm
      CAUTION:

      Clean the bolts and nuts before reusing.

      Replace the bolts and nuts if damaged.

      Replace the self-locking bolts and nuts after removing

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).

      CAUTION:

      Deformation increases the risk of damage.

      - Do not hold the brake booster on the actuator rod.

    • Refer to BRAKE BOOSTER, REMOVING AND INSTALLING, VACUUM BRAKE BOOSTER 
17. Seal
    • Replace after removing.
18. Push Rod
    • The pushrod is only loosely inserted into the brake master cylinder and can fall into the brake booster when removing
19. Actuator Pin
    • For the Brake Lamp Switch -F-
    • 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, BRAKE LAMP ACTUATOR ROD 
20. Brake Lamp Switch -F-
    • Refer to BRAKE LAMP SWITCH, REMOVING AND INSTALLING
21. Bolt
    • 8 Nm
    • The brake lamp switch must be flush with the outer edge of the mount
      CAUTION:

      Clean the bolts and nuts before reusing.

      Replace the bolts and nuts if damaged.

      Replace the self-locking bolts and nuts after removing

22. Brake Line
    • 16 Nm
    • Brake master cylinder/primary piston circuit to hydraulic unit

Brake Booster Ball Head, Adjusting

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI OF AMERICA, LLC

• Dimension -a- = 164.8 mm ± 0.6 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