Removing and installing brake master cylinder/hydraulic servo unit — AUDI

Notes:

Brake master cylinders cannot be dismantled any further, i.e. no provision is made for servicing.
Use only fresh brake fluid. Refer to information on brake fluid reservoir.

Brake fluid reservoir with float indicator
Fill up with brake fluid to "Max" mark

Functional check of indicator:

With ignition on, press firmly on centre of cap (membrane). Warning lamp in instrument cluster lights and acoustic alarm sounds.

Diaphragm was discontinued as of 07/92. To check indicator, unscrew yellow cap with brake symbol and press by hand on visible strainer with ignition switched on.
Connection for hydraulic coupling is located on side

Sealing plug
Moisten with brake fluid and insert into brake master cylinder
Press brake fluid reservoir into sealing plugs

Brake master cylinder
ø 25.4 mm
Replace as complete unit if necessary.

Double-ended bolts, 25 Nm
For attachment of brake line bracket, screw M8 nut onto right end

Brake lines
Unscrew

Warning switch, 20 Nm
For monitoring pressure of hydraulic servo unit; if pressure drops to a value between 127 and 87 bar, warning lamp in dash insert lights and buzzer sounds
Screw into servo unit

Oil seal
Always replace

Hexagon nut, 20 Nm

Mounting
Oil seal
Oil seal
Always replace
Attach to adapter before installing servo unit
Roll onto bulkhead after attaching servo unit

Hexagon nut, 20 Nm
Pressure pipe
Pressure accumulator/servo unit

Before removing, dissipate operating pressure by pressing brake pedal roughly 20 times with engine switched off

Return pipe
Servo unit - reservoir

Hydraulic servo unit
Do not press brake pedal with brake master cylinder removed

Lock nut
Circlip
Always replace
Fit onto pin

Clevis
Adjusting:

Vehicles with hydraulic brake servo: => Fig.
1

Pin
Grease slightly before inserting

Bulkhead
Self-locking nut, 25 Nm
Always replace

Pedal bracket

Fig.1
Adjusting clevis, vehicles with hydraulic brake servo

LHD vehicles:

a = 225.0 ± 0.5 mm

RHD vehicles

a = 202.0 ± 0.5 mm

Notes:

Pull out of servo as far as stop prior to measurement
When measuring, the ball head should be aligned at right angles to the surface of the brake servo unit.