Brake master cylinder — VW

Version

The brake master cylinder consists out of one cast part as well as the flange to fit the cylinder. To which the brake fluid reservoir line is connected with an elbow. The elbow is fitted with a sealing plug. A protective cap, fitted on the flange side, protects the brake cylinder against dust and humidity.

Function

Brake master cylinder version

1 -
Piston
2 -
Filling hole
3 -
Intermediate washer
4 -
Primary boot
5 -
Floor valve
6 -
Spring
7 -
Compensating hole
8 -
Secondary boot
9 -
Thrust washer
10 -
Circlip

The piston (1) produces the pressure needed to operate the brakes in the master cylinder. The brake fluid flows via the filling hole (2) into the filling chamber, then crosses the piston holes, the intermediate washer (3) and the primary boot (4), and finally into the pressure chamber. The brake fluid must be able to flow constantly into the filling chamber to avoid air coming into the pressure chamber, caused by a higher volume produced when resetting the piston. The brake fluid can flow back in the brake circuit via the floor valve (5) fitted by the spring (6) when the piston is activated, and flows after a braking procedure in the master cylinder again. The flow valve maintains a constant pressure of 0.5 to 1.5 kg/cm2 to reduce the reaction time when applying the brakes.

After the braking procedure excessive brake fluid flows into the expansion tank again via the hole (7). Therefore the primary boot must never close the hole when the brake is in rest position. The brake cylinder is closed via the secondary boot (8), the thrust washer (9) and the safety ring (10).

Removing and installing brake master cylinder

1.- Evacuate brake fluid out of the expansion tank with an aspirator.

Brake fluid is poisonous. Also due to its corrosive nature it must not come into contact with paintwork.
2.- Take elbows out of the seals and unscrew brake lines on brake master cylinder.

3.- Unscrew brake master cylinder from chassis.

Note:

Spacer sleeves are fitted on the cross member. When loosening the bolts take care that the sleeves do not fall into the workshop pit.

4.- Fit brake master cylinder to chassis.

5.- Lubricate elbows and seals with brake fluid and install elbows.

6.- Fit brake lines.

7.- Adjust push rod =>Page
46-24

8.- Bleed brake system =>pages
47-12

To avoid brake lines securing nuts being damaged and to facilitate removing and fitting it should be used key with Part No. VW 000 220.