brake fluid 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)
Pa
ge 1 of 11 Brake master c
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

47-42


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
Pa
ge 2 of 11 Brake master c
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

47-43


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.
Pa
ge 3 of 11 Brake master c
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

47-44


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
Pa
ge 4 of 11 Brake master c
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

47-48

- 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.
Pa
ge 8 of 11 Brake master c
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

CAUTION!
Brake fluid must not be allowed to come into contact with paintwork
because of its caustic effect.
Pa
ge 9 of 11 Brake master c
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

47-49

- 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.
Pa
ge 10 of 11 Brake master c
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

47-50

Installing
Note the following points:

- Adjust brake light switch page 46
-50
.

- Adjust vent valve for cruise control system
page 46
-54
.
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.

- Bleed brake system page 47
-23
.
Pa
ge 11 of 11 Brake master c
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