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

Fig 1: Exploded View Of Brake Booster/Master Brake Cylinder (Vacuum Brake Booster)

Courtesy of AUDI OF AMERICA, LLC

1. Nut
   • 23 Nm
2. Heat Shield
   • Not installed on all models
3. Brake Master Cylinder
   • Cannot be serviced. If malfunctioning, replace as complete unit.
   • The brake master cylinder and brake booster can be replaced independently of one another.
   • Before installing check if the actuator pin for the brake lamp switch as well as the piston are inserted. Refer to the appropriate Service Information .
   • Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING, VACUUM BRAKE BOOSTER 
4. Brake Line
   • 14 Nm
   • Brake master cylinder/primary piston circuit to hydraulic unit
5. Brake Line
   • 14 Nm
   • Brake master cylinder/secondary piston circuit to hydraulic unit
6. Bolt
   • 8 Nm
7. Brake Lamp Switch -F-
   • No function of the brake lamp due to missing actuator pin for the brake lamp switch. Refer to the appropriate Service Information .
   • Refer to BRAKE LAMP SWITCH, REMOVING AND INSTALLING
8. Brake Fluid Level Warning Switch -F34-
   • Refer to Brake Fluid Level Warning Switch -F34-, REMOVING AND INSTALLING, VACUUM BRAKE BOOSTER 
9. Brake Fluid Reservoir
   • Refer to BRAKE FLUID RESERVOIR, REMOVING AND INSTALLING, VACUUM BRAKE BOOSTER 
10. Locating Pin or Stud Bolt
    • Tighten the stud bolt to 5 Nm
    • Slide through the brake fluid reservoir and the master brake cylinder
    • The locking pin must be pushed into the brake fluid reservoir tab.
11. Cap
    • With gasket
    • Seal cannot be ordered
12. Vacuum Hose
    • With check valve
13. Seal
    • Replace after removing.
14. Plugs
    • To install, coat with brake fluid
15. Brake Booster
    • Function Test:

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

    • The brake master cylinder and brake booster can be replaced independently of one another.
    • Refer to BRAKE BOOSTER, REMOVING AND INSTALLING, VACUUM BRAKE BOOSTER 
16. Seal
    • Replace after removing.
17. Nut
    • Tightening specification and sequence. Refer to Fig 2.
    • Replace after removing.
    • Self-locking
18. Seal
    • Replace after removing.
19. Rubber Buffer

Brake Booster - Tightening Specification and Sequence 

Fig 2: Brake Booster - Tightening Sequence

Courtesy of AUDI OF AMERICA, LLC

-- Tighten the nuts to 25 Nm in the sequence -3 and 4-.