Overview - Brake Booster/Brake Master Cylinder

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

Courtesy of AUDI OF AMERICA, LLC

1. Brake Fluid Reservoir
   • Refer to BRAKE FLUID RESERVOIR, REMOVING AND INSTALLING 
2. Seal
   • Replace if damaged
   • Not available separately.
3. Cap
4. Brake Fluid Level Warning Switch -F34-
   • Refer to Brake Fluid Level Warning Switch -F34-, REMOVING AND INSTALLING 
5. Seal
   • Replace after removing.
6. Seal
   • Replace after removing.
7. 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.

     TIP:

     Clean all sealing surfaces before installing the brake booster.

     The brake booster contact surface on the bulkhead must not be damaged or deformed.

     The ball head on the brake booster must be properly positioned and tightened. Adjust the ball head. Refer to Fig 2.

     Check the boot on the brake booster for damage.

     The boot on the brake booster must not be damaged.

8. Seal
   • Replace after removing.
9. Push Rod
   • Not available separately.
   • The pushrod is only loosely inserted into the brake master cylinder and can fall into the brake booster when removing
10. Actuator Pin
    • For the Brake Lamp Switch -F-
    • The actuator pin must be inserted, otherwise the brake lamp will not work. Refer to Installing - Make sure that the actuator pin -2- for the brake lamp is inserted in the brake master cylinder -1-. .
    • The actuator pin cannot be replaced separately
11. Brake Lamp Switch -F-
    • Refer to BRAKE LAMP SWITCH, REMOVING AND INSTALLING 
12. Bolt
    • 8 Nm
13. Brake Line
    • 14 Nm
    • Brake master cylinder/primary piston circuit to hydraulic unit
14. Brake Line
    • 14 Nm
    • Brake master cylinder/secondary piston circuit to hydraulic unit
15. Brake Master Cylinder
    • Replace completely if faulty
    • Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING 
16. Bolt
    • 25 Nm
17. Nut
    • 23 Nm
18. Plugs
    • To install, coat with brake fluid
19. Bolt
    • 8 Nm

Adjusting the Brake Booster Ball Head 

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI OF AMERICA, LLC

Refer to BRAKE BOOSTER, REMOVING AND INSTALLING 

• Dimension -a- = 164.7 mm ± 0.5 mm

Tightening Specification