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

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

Courtesy of AUDI

Brake Line
- 14 Nm
- Replace a damaged or bent brake line
- Brake master cylinder/secondary piston circuit to hydraulic unit
- Do not change the bending shape.
Brake Master Cylinder
- There are different versions. Refer to the appropriate Electronic Parts Information for the allocation.
- Replace completely if faulty
- Refer to BRAKE MASTER CYLINDER, REMOVING AND INSTALLING
Bolt
- 25 Nm
Nut
- Tightening Specification
  - 49 Nm for the brake booster / brake master cylinder, ZF-Girling
  - 55 Nm for the brake booster / brake master cylinder, Bosch
- Replace after removing
Plugs
- To install, coat with brake fluid
Locking Pin
- 8 Nm
Brake Fluid Reservoir
- There are different versions. Refer to the appropriate Electronic Parts Information for the allocation.
Seal
- Not available separately.
Cap
Rubber Buffer
Protective Plate
- Equipped on some models
Rubber Buffer
Bolt
- 8 Nm
Brake Fluid Level Warning Switch -F34-
- Refer to Brake Fluid Level Warning Switch -F34-, REMOVING AND INSTALLING
Seal
- Replace after removing
Brake Booster
- There are different versions. Refer to the appropriate Electronic Parts Information for the allocation.
- 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
- Refer to BRAKE PEDAL, DISCONNECTING FROM BRAKE BOOSTER
- Refer to Fig 2
Seal
- Replace after removing
Push Rod
- The pushrod is only loosely inserted into the brake master cylinder and can fall into the brake booster when removing
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
Brake Lamp Switch -F-
- Refer to BRAKE LAMP SWITCH, REMOVING AND INSTALLING
- Must be flush with the outer edge of the mount
Bolt
- 8 Nm
Brake Line
- 16 Nm
- Replace a damaged or bent brake line
- Brake master cylinder/primary piston circuit to hydraulic unit
- Do not change the bending shape.

Vacuum Brake Booster Ball Head, Adjusting

Fig 2: Adjusting the Brake Booster Ball Head

Courtesy of AUDI

CAUTION:

Risk of overheating the brakes due to the incorrect positioning of the actuator rod.

- Before installing the brake booster, adjust the actuator rod length with the ball head to the correct dimension.

Depending on the version, the ball head may already be set to the right dimension.

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

Component		Nm
Ball head to brake booster		30