Master Cylinder and Brake Booster Assembly Overview

Master Cylinder and Brake Booster Assembly Overview






1 ABS Control Module (w/EDL) (J104)

• Removal and installation, refer to => [ Control Module and Hydraulic Unit ] Control Module and Hydraulic Unit.

2 ABS Hydraulic Unit (N55)

• Removal and installation, refer to => [ Control Module and Hydraulic Unit ] Control Module and Hydraulic Unit.

3 Brake Line, 14 Nm

• Master brake cylinder/primary piston circuit to hydraulic control unit.

• Identification: Identification: tube fitting with M10 x 1 or M12 x 1 thread.


During production, the thread was changed from M10 x 1 to M12 x 1.

4 Brake Line, 14 Nm

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

• Identification: Pipe bolt with thread M12 x 1.

5 Brake Line, 14 Nm

• To left front brake caliper.

• Identification: Identification: tube fitting with M12 x 1 or M10 x 1 thread.


During production, the thread was changed from M10 x 1 to M12 x 1.

6 Brake Line, 14 Nm

• To right front brake caliper.

• Identification: Identification: tube fitting with M10 x 1 or M12 x 1 thread.


During production, the thread was changed from M10 x 1 to M12 x 1.

7 Brake Line, 14 Nm

• To left rear brake caliper.

• Identification: Pipe bolt with thread M12 x 1.

8 Brake Line, 14 Nm

• To right rear brake caliper.

• Identification: Pipe bolt with thread M10 x 1.

9 Bolt, 5.5 Nm

• Use new bolts.

10 Bracket

11 Bolt, 8 Nm

12 Gasket

• For brake booster.

13 Brake Booster

• On gasoline engines, vacuum is supplied from intake manifold.

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

• Function test:

- Forcefully press brake pedal several times with engine switched off. This dissipates any vacuum present in the unit.

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

• If malfunctioning: replace as complete unit.

• Removal and installation, refer to => [ Brake Booster ] Brake Booster.

14 Seal

15 Dual Master Brake Cylinder

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

• Removal and installation, refer to => [ Master Cylinder ] Master Cylinder.

16 Nut, 25 Nm

• Always replace after removal.

17 Sealing Plugs

• Moisten with brake fluid and press into brake fluid reservoir.

18 Brake Fluid Reservoir

19 Cap

20 Sealing Plugs

• Connection for vacuum hose.

21 Vacuum Hose

• Insert into brake booster.

22 Brake Booster Pressure Sensor (G294)

• On vehicles with FSI engine, without Hydraulic Brake Vacuum Booster.

• Removal and installation, refer to => [ Brake Booster Pressure Sensor ] Brake Booster Pressure Sensor.