Brake Booster and Master Cylinder Overview

Brake Booster and Master Cylinder Overview

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






1 Pedal Assembly

2 Nut

• 25 Nm

• Always replace if removed.

3 Gasket

• For the brake booster.

4 Brake Booster

• On gas engines, the required vacuum is supplied either by the intake manifold or by a mechanical vacuum pump.

• Some gas engines with a Direct Shift Gearbox (DSG(R)), but not having an hydraulic brake booster, have an electric brake system vacuum pump. Refer to => [ Brake System Vacuum Pump V192 ] Service and Repair.

• On diesel engines, a vacuum pump is installed, for vacuum creation. Refer to => [ Brake Booster Vacuum Pump ] Description and Operation.

• Functional Check:

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

- 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).

• Replace completely if there are malfunctions (check the vacuum system for the brake booster first; refer to => [ Brake Booster Vacuum System, Checking ] Testing and Inspection).

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

5 Seal

6 Brake Master Cylinder

• Allocation, refer to the Parts Catalog.

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

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

7 Brake Lamp Switch (F)

• Includes the brake pedal switch.

• Removing and installing, refer to => [ Brake Lamp Switch F ] Service and Repair.

8 Inner TORX(R) Bolt

• 5 Nm

9 Clip

10 Heat Shield

11 Nut

• 25 Nm

• Always replace if removed.

12 Brake Line

• 14 Nm

• Master cylinder secondary piston circuit to hydraulic unit.

13 Brake Line

• 14 Nm

• Master cylinder primary piston circuit to hydraulic unit.

14 Plug

• Lubricate with brake fluid and press into the brake fluid reservoir.

15 Brake Fluid Reservoir

16 Cap

17 Vacuum Hose

• Insert into the brake booster

18 Vacuum Sensor (G608)

• On vehicles with a hydraulic brake booster.

• Removing and installing, refer to => [ Vacuum Sensor G608 ] Vacuum Sensor G608.

• Some vehicles without a hydraulic brake booster have a brake booster pressure sensor.

• brake booster pressure sensor removing and installing. Refer to => [ Brake Booster Pressure Sensor G294 ] Brake Booster Pressure Sensor G294.

19 Grommet

• Connection for the vacuum hose.