Overview - Brake Booster/Brake Master Cylinder

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

Courtesy of AUDI

1. Brake Line
   • Brake master cylinder/secondary piston circuit to hydraulic unit
   • 14 Nm
2. Brake Master Cylinder
   • Replace completely if faulty
   • Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING 
3. Bolt
   • 25 Nm
4. Nut
   • Replace after removing
   • 49 Nm
5. Plugs
   • To install, coat with brake fluid
6. Locking Pin
   • 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.
   • 8 Nm
7. Brake Fluid Reservoir
   • 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
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.
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-
    • The actuator pin only functions for the brake lamp, not for the brake system
    • If the pin is missing or is damaged, the brake lamp will not function
    • Must not fall in the brake booster when removing the brake master cylinder.
    • It must always be pushed into the hole in the brake master cylinder directly on the Brake Lamp Switch -F-
    • Do not bend it
    • Cannot be replaced separately
20. Brake Lamp Switch -F-
    • Refer to BRAKE LAMP SWITCH, REMOVING AND INSTALLING
21. Bolt
    • The brake lamp switch must be flush with the outer edge of the mount
    • 8 Nm
22. Brake Line
    • Brake master cylinder/primary piston circuit to hydraulic unit
    • 16 Nm

Brake Booster Ball Head, Adjusting

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI

• Dimension -a- = 164.7 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 gasket installed.

Tightening Specifications