Brake Booster/Master Cylinder Assembly Overview

Brake Booster/Master Cylinder Assembly Overview

• Use only new brake fluid. Observe information on the brake fluid reservoir!





1 Pedal assembly

• Various versions.

2 Nut, 25 Nm

• Self locking

• Always replace after removal

3 Gasket

• For the brake booster.

4 Brake booster

• On gas engines, vacuum is supplied from the intake manifold.

• Some vehicles with gas engine and automatic transmissions are equipped with a brake system vacuum pump. Refer to --> [ Brake System Vacuum Pump ] Brake System Vacuum Pump.

• On vehicles with a hydraulic brake booster, a vacuum sensor is installed. Refer to --> [ Brake Booster Vacuum Sensor ] Brake Booster Vacuum Sensor.

• On diesel engines, a vacuum pump is installed for vacuum creation. Refer to --> [ Brake Booster Vacuum Pump Overview ] Brake Booster Vacuum Pump Overview.

• Functional test:

- With the engine turned off, press the brake pedal firmly several times (to deplete vacuum in brake booster).

- Press and hold the brake pedal with average foot pressure and start the engine. If the brake booster is working properly, the pedal will be felt to give noticeably under foot (booster assistance becomes effective).

• If malfunctioning: replace as complete unit.

• Removing and installing, refer to --> [ Brake Booster ] Brake Booster.

5 Seal

6 Brake booster vacuum sensor (G483)

• Only on vehicles with the hydraulic brake booster.

• Removing and installing, refer to --> [ Brake Booster Vacuum Sensor ] Brake Booster Vacuum Sensor.

7 Master cylinder, without brake light switch

• Cannot be serviced. Replace as complete unit if malfunctioning.

• Removing and installing, refer to --> [ Master Cylinder ] Master Cylinder.

8 Master cylinder, with brake light switch

• Cannot be serviced. Replace as complete unit if malfunctioning.

• Removing and installing, refer to --> [ Master Cylinder ] Master Cylinder.

9 Brake light switch (F)

• Includes the brake pedal switch.

• On vehicles through 12.09.05, the brake light switch is located on the brake pedal. Refer to --> [ Brake Pedal Assembly Overview ] Brake Pedal Assembly Overview.

• Removing and installing, refer to --> [ Brake Light Switch, from 12.11.05 ] Brake Light Switch, from 12.11.05.

10 Torx bolt, 5 Nm

11 Heat shield

12 Nut, 25 Nm

• Self locking

• Always replace after removal

13 Brake line, 14 Nm

• Master cylinder/secondary piston circuit to hydraulic control unit.

14 Brake line, 14 Nm

• Master cylinder/primary piston circuit to hydraulic control unit

15 Sealing plugs

• Coat with brake fluid and press into the brake fluid reservoir

16 Brake fluid reservoir

17 Cap

18 Sealing plugs

• Connection for vacuum hose.

19 Vacuum hose

• Insert into the brake booster.

20 Brake booster pressure sensor (G294)

• On vehicles with Fuel Straight Injection (FSI) engines without hydraulic Brake vacuum booster.

• Removing and installing, refer to --> [ Brake Booster Pressure Sensor ] Brake Booster Pressure Sensor.