Overview - Brake Booster/Brake Master Cylinder

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

Courtesy of AUDI OF AMERICA, LLC

1. Brake Line
   • 14 Nm
   • Brake master cylinder/secondary piston circuit to hydraulic unit
2. Brake Master Cylinder
   • Replace completely if faulty
   • Removing and installing. Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING 
     NOTE:

     Completely replace the brake master cylinder if it is malfunctioning.

3. Bolt
   • 25 Nm
4. Nut
   • 23 Nm
   • Always replace 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 (87 psi).
   • 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.
     NOTE:

     Tighten the bolt for the brake fluid reservoir steel cap to 8 Nm.

   • Removing and installing. Refer to BRAKE FLUID RESERVOIR, REMOVING AND INSTALLING 
8. Seal
   • Replace if damaged
9. Cap
   • 1.5 ± 0.5 Nm
   • For the brake fluid reservoir
10. Brake Fluid Level Warning Switch -F34-
    • After assembly, press on the hook for a secure fit.
    • Removing and installing. Refer to Brake Fluid Level Warning Switch -F34-, REMOVING AND INSTALLING 
11. Seal
    • Always replace after removing
12. 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).

    • Removing and installing. Refer to BRAKE BOOSTER, REMOVING AND INSTALLING 
    • Adjust the ball head. Refer to Fig 2.
      NOTE:

      Completely replace the brake booster if it is malfunctioning. Check the brake booster vacuum system beforehand.

13. Gasket
    • Always replace after removing
14. Push Rod

    The push rod is only loosely pressed in the brake master cylinder and can fall into the brake booster when removing.

15. 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 .
16. Brake Lamp Switch -F-
    • Removing and installing. Refer to BRAKE LAMP SWITCH, REMOVING AND INSTALLING
17. Bolt
    • 8 Nm
18. Brake Line
    • 14 Nm
    • Brake master cylinder/primary piston circuit to hydraulic unit

Adjusting the Brake Booster Ball Head

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI OF AMERICA, LLC

Dimension -a- = 164.7 mm ± 0.5 mm

Tightening Specification