AUDI A4 1999 B5 / 1.G Master Cylinder 25mm Workshop Manual

47-41


Brake master cylinder with 25.4
mm (0.999 in.) diameter piston
and brake servo, component
summary Note:

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 -
Brake master cylinder
Diameter: 25.4 mm (0.999 in.)Cannot be repaired. If malfunctioning,
replace as complete unit only. Must be removed and installed together
with the brake servo Removing and installing page 47
-46
2 -
T45 Torx
25 Nm (18 ft lb)
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ylinder with 25.4 mm
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3 -
Flange nut
Always replace50 Nm (37 ft lb)
4 -
Sealing plug Moisten with brake fluid and insert into
brake master cylinder Press brake fluid reservoir into sealing
plugs
5 -
Brake fluid reservoir with brake fluid level
warning switch
Functional check:
- Remove brake fluid reservoir cap and
with the ignition switched on push on
strainer in reservoir.
- The warning light in the instrument panel
insert comes on and an audible warning
signal sounds. Removing and installing page 47
-46
Fluid couplings are on the side of the
reservoir Pay attention to information found on the
label on the reservoir before adding fluid
6 -
Seal
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7 -
Brake fluid reservoir cap
8 -
Fluid supply hose
From brake fluid reservoir to clutch master
cylinder
9 -
Seal Install in groove in brake master cylinderReplace after removing brake master
cylinder
10 -
Brake servo Removing and installing page 47
-46
Adjusting ball head Fig. 1
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 unit is working properly, pedal will
be felt to give slightly under foot (servo
assistance becomes effective).
If malfunctioning:
- Replace as complete unit only.
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ylinder with 25.4 mm
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11 -
Gasket
Brake servo supplied with gasket glued onReplace only if damaged
12 -
Vacuum hose
- Install into brake servoOn gasoline engines vacuum is supplied
from intake manifold
13 -
Bulkhead
14 -
Brake line 15 Nm (11 ft lb)Brake master cylinder/primary piston circuit
to hydraulic control unit
15 -
Brake line 15 Nm (11 ft lb)Brake master cylinder/secondary piston
circuit to hydraulic control unit
16 -
Bolt Screw in as far as stopAttaches brake fluid reservoir
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ylinder with 25.4 mm
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piston and brake servo, com
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a = 159 mm 0.5 mm (6.26 in. 0.02 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 25.4 mm
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piston and brake servo, com
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47-46

Brake master cylinder with 25.4 mm
(0.999 in.) diameter piston and brake
servo, removing and installing as a unit


Special tools and equipment

Repair Manual, Body-Exterior
Repair Manual, Body-Interior
Sealing plugs from repair kit, Part No. 1H0 698
311A
T10006 Brake pedal release tool

CAUTION!

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

Removing

- Remove driver's side storage compartment.

Repair Manual, Body
-Interior, Repair Group
68

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ylinder with 25.4 mm
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) diameter
piston and brake servo, com
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Releasing brake pedal
- Remove brake light switch.
1 -
Inserting T10006 brake pedal release tool
Insert the tool from below
2 -
Release procedures
- Tightly hold brake pedal.
- Lift catches off ball head using a slight
pull on tool (arrow -A-).
- Tension tool so catches do not re-
engage ball head.
- Pull brake pedal from ball head (arrow -
B-).
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ylinder with 25.4 mm
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- 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.

- Remove bolt -3- attaching brake fluid reservoir -4-.
- Disconnect harness connector -2- to brake fluid level warning switch.

Note: - On vehicles with manual transmissions, disconnect clutch master
cylinder supply hose -1- and seal with plug.
Cover plenum to catch any spilled brake fluid.The brake fluid reservoir is attached to the master cylinder on the
bottom side.
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ylinder with 25.4 mm
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piston and brake servo, com
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CAUTION!
Brake fluid must not be allowed to come into contact with paintwork
because of its caustic effect.
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ylinder with 25.4 mm
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) diameter
piston and brake servo, com
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- Remove brake fluid reservoir by pressing locking
catch down and pulling reservoir out of sealing
plugs.

- Disconnect brake lines -3- on brake master cylinder and seal brake
lines and threaded holes using plugs from repair kit.
- Disconnect vacuum hose -2- from brake servo.
-
Remove T45 Torx bolts -1- from brake servo.- Remove brake servo together with brake master cylinder as a unit.

Note:
Pay particular attention to the following when installing: - Remove nuts -1- attaching brake master cylinder to brake servo.
- Carefully separate brake master cylinder from brake servo.
Clean any spilled brake fluid from the plenum before installing brake
servo and master cylinder. When bolting the brake master cylinder to the brake servo make sure
pushrod is correctly located in the master cylinder.
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ylinder with 25.4 mm
(0.999 in.
) diameter
piston and brake servo, com
ponent summar
y
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU03.47.7