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

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

Courtesy of AUDI OF AMERICA, LLC

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, WITH VACUUM BRAKE MASTER CYLINDER 
3. Bolt
   • 23 Nm
4. Nut
   • 23 Nm
5. Plugs
   • To install, coat with brake fluid
6. Stud Bolt
   • 8 Nm
7. Brake Fluid Reservoir
   • Fill pressure maximum 6 bar (87.02 psi).
   • Refer to BRAKE FLUID RESERVOIR, REMOVING AND INSTALLING 
8. Seal
   • Replace if damaged
9. Cap
10. Cover
    • For the brake fluid reservoir
11. Bolt
    • 8 Nm
12. Brake Fluid Level Warning Switch -F34-
    • Refer to Brake Fluid Level Warning Switch -F34-, REMOVING AND INSTALLING 
13. Seal
    • Always replace after removing
14. 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.
15. Seal
    • Always replace after removing
16. Seal
    • Always replace after removing
17. 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

18. Actuator Pin
    • For the Brake Pedal Switch -FX2-
    • 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
19. Brake Pedal Switch -FX2-
    • with
      • Brake Lamp Switch -F-
      • Brake Pedal Position Sensor -G100-
    • Refer to Brake Pedal Position Sensor -G100-, REMOVING AND INSTALLING
20. Bolt
    • 8 Nm
21. Brake Line
    • Brake master cylinder/primary piston circuit to hydraulic unit
    • 14 Nm

Brake Booster Ball Head, Adjusting

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI OF AMERICA, LLC

• Dimension -a- = 164.7 mm ± 0.5 mm

TIP: 

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 Specification