AUDI A4 1997 B5 / 1.G Master Cylinder 23mm Workshop Manual

47-29


Brake master cylinder with
23.81 mm (0.937 in.) piston
diameter and brake servo,
component summary Note:

Brake master cylinders and brake servos can
be replaced separately.
Brake master cylinders can no longer be
disassembled, i.e. there is no provision for
servicing.
Use only fresh brake fluid. Pay attention to
information on the brake fluid reservoir.
Brake line connections to master cylinder,
Bosch 5.0 ABS system ( page 45
-6 ), Bosch
5.3 system ( page 45
-18
).
1 -
T45 Torx
25 Nm (18 ft lb)
2 -
Self-locking nut 49 Nm (36 ft lb)
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47-30


3 -
Brake master cylinder
Diameter: 23.81 mm (0.937 in.)Cannot be repaired. If malfunctioning,
replace as complete unit only. Removing and installing page 47
-34
4 -
Brake line
15 Nm (11 ft lb)Brake master cylinder/secondary piston
circuit to hydraulic control unit
5 -
Brake line 15 Nm (11 ft lb)Brake master cylinder/primary piston circuit
to hydraulic control unit
6 -
Seal Always replace
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47-31


7 -
Brake servo
On gasoline engines vacuum is supplied
from the intake manifold On Diesel engines vacuum is supplied from
the vacuum pump
Functional check:
- With engine switched off, depress brake
pedal firmly several times (to deplete
vacuum in brake servo).
- Depress and hold brake pedal with
average foot pressure and start engine. If
servo is working properly, pedal will be
felt to give slightly under foot (servo
assistance becomes effective).
If malfunctioning:
- Replace as complete unit only.Check valve in vacuum hose - 9 -Removing and installing page 47
-37
Adjusting ball head Fig. 1
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8 -
Gasket
9 -
Vacuum hose
Insert into brake servo
10 -
Brake fluid reservoir
11 -
Fluid reservoir cap
12 -
Sealing plugs
13 -
Supply hose Where applicableFrom brake fluid reservoir to clutch master
cylinder
14 -
Bulkhead
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ylinder with 23.81 mm
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Dimension -A- = 159 0.5 mm (6.26 0.020 in.)
Note: Fig. 1 Adjusting ball head
The ball head must be positioned at right angles to the mounting
surface of the brake servo unit when measuring. Measure up to end of ball head with no gasket installed.
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ylinder with 23.81 mm
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47-34

Brake master cylinder with 23.81 mm
(0.937 in.) diameter piston, removing
and installing


Special tools and equipment
Sealing plugs from repair kit, Part No. 1H0 698
311A

CAUTION!

Part numbers are listed here for reference
only. Always check with your Parts
department for the latest information.

Removing

- Attach bleeder hose and bleeder bottle to left-
front brake caliper bleeder screw and open
bleeder screw.

- Operate brake pedal to pump out as much brake
fluid as possible.

- Close left-front bleeder screw.

- Cover engine compartment to catch any spilled
brake fluid.

CAUTION!
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ylinder with 23.81 mm
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Brake fluid must not be allowed to come into
contact with paintwork because of its caustic
effect.
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ylinder with 23.81 mm
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- On vehicles with manual transmission, disconnect clutch master
cylinder supply hose -1- and seal with plug.
- Disconnect harness connector from brake fluid level warning switch -2-.

- Disconnect brake lines -1- on brake master cylinder and seal brake
lines and threaded holes using plugs from repair kit.
- Remove brake master cylinder mounting nuts -2-.
- Carefully remove brake master cylinder from brake servo.
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ylinder with 23.81 mm
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Installing
When installing, note the following points:

- When installing brake master cylinder onto
brake servo, make sure push rod is correctly
located in brake master cylinder.

- Apply slight pressure to brake pedal to move
push rod toward brake master cylinder; this
makes it easier to guide brake master cylinder
onto push rod.

Bleeding clutch hydraulics

- Connect US1116 brake bleeder but do not
switch on yet.

- Open bleeder screw on clutch slave cylinder.

- Attach collector bottle hose.

- Switch on bleeder unit and allow approx. 100 cc
(6 oz.) of brake fluid to flow out of clutch slave
cylinder.

- Close bleeder screw.

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ylinder with 23.81 mm
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- Bleed brake system page 47
-23
.
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ylinder with 23.81 mm
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) piston diameter and brake servo, com
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