Audi 2003 A8 Instruction manual

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Workshop Manual
Audi A8 2003 ➤
Brake system
Edition 03.2013
Service
Service Department. Technical Information

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
List of Workshop Manual Repair GroupsList of Workshop Manual
Repair GroupsList of Workshop Manual Repair Groups
Repair Group
00 - Technical data
45 - Anti-lock brake system
46 - Brakes - mechanism
47 - Brakes - hydraulics
Technical information should always be available to the foremen and mechanics, because their
careful and constant adherence to the instructions is essential to ensure vehicle road-worthiness and
safety. In addition, the normal basic safety precautions for working on motor vehicles must, as a
matter of course, be observed.
Service
All rights reserved.
No reproduction without prior agreement from publisher.
Copyright © 2013 Audi AG, Ingolstadt A0051005420

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Contents
00 - Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Brakes, wear limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Assessment of ceramic brake discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Visible features of ceramic brake discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Superficial cracks in cooling channel lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Cracks in area of bolted connection on ceramic brake discs . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4 Edge fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.5 Chipping on ceramic brake discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.6 Cracks extending into cooling channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Assessing degree of wear on ceramic brake discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Wear assessment by checking thickness of brake disc . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Wear assessment according to wear indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Wear assessment by weighing brake disc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4 Wear assessment by weighing brake disc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4 Brake test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1 General notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2 Vehicles with front-wheel drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Vehicles with four-wheel drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.4 EPB (Electronic Parking Brake) on brake dynamometer . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5 Brake fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1 General notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
45 - Anti-lock brake system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1 General information on the anti-lock brake system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.1 Notes for repair work on the ABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2 Connecting VAS 505x and selecting functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Electronic stabilisation program Bosch 5.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1 Overview of components - ESP Bosch 5.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2 Hydraulic unit and brake lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Removing and installing hydraulic control unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4 Renewing ABS control unit J104 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4 Removing and installing parts of ABS system on front and rear axles . . . . . . . . . . . . . . . . 31
4.1 Removing and installing parts of ABS system on front axle . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2 Removing and installing parts of ABS system on rear axle . . . . . . . . . . . . . . . . . . . . . . . . 32
5 Removing and installing parts of ESP system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.1 Removing and installing brake light switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.2 Removing and installing lateral acceleration sender G200 and yaw rate sender G202 . . 35
5.3 Removing and installing steering angle sender G85 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.4 Removing and installing parking brake switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.5 Removing and installing brake pressure sender G201 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
46 - Brakes - mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1 Front brakes (PR 1LG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.1 Servicing front brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.2 Removing and installing brake pads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
1.3 Renewing brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2 Front brakes (PR 1LJ, 1LL, 1LM, 1LK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.1 Servicing front brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.2 Removing and installing brake pads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.3 Renewing brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3 Ceramic front brakes (PR 1LW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Audi A8 2003 ➤
Brake system - Edition 03.2013
Contents i

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
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with respect to the correctness of information in this document. Copyright by AUDI AG.
3.1 Servicing ceramic brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.2 Detaching and attaching damper spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.3 Removing and installing brake pads (ceramic brakes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.4 Removing and installing brake caliper (ceramic brakes) . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.5 Detaching and attaching front brake disc (ceramic brakes) . . . . . . . . . . . . . . . . . . . . . . . . 62
3.6 Renewing front brake disc (ceramic brakes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4 Rear brakes, electronic parking brake and handbrake (EPB) . . . . . . . . . . . . . . . . . . . . . . 65
4.1 Servicing rear brakes - all models including ceramic brakes . . . . . . . . . . . . . . . . . . . . . . 65
4.2 Removing and installing brake pads (rear brakes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5 Brake pedal (LHD) - exploded view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.1 Separating brake pedal from brake servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.2 Removing and installing brake pedal (LHD vehicles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
6 Removing and installing mounting bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.1 Removing and installing mounting bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7 Overview of components: electronic parking brake and handbrake (EPB) . . . . . . . . . . . . 78
7.1 Removing and installing control unit for electronic parking brake and handbrake . . . . . . . . 79
7.2 Removing and installing actuator motor for electronic parking brake and handbrake . . . . 79
47 - Brakes - hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
1 Pressurised leak test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
1.1 Pressurised leak test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
1.2 High-pressure and low-pressure tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
2 Brake calipers FNR G60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2.1 Servicing brake calipers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2.2 Removing and installing piston for front brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
3 Brake calipers 2FNR 42 AL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.1 Servicing brake calipers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.2 Removing and installing pistons for front brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4 Brembo brake calipers (18") . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.1 Servicing brake calipers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.2 Removing and installing pistons for front brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5 Brake caliper (ceramic brakes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1 Servicing brake caliper (ceramic brakes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.2 Removing and installing pistons for front brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6 Rear brake calipers for electronic parking brake and handbrake (EPB) . . . . . . . . . . . . . . 100
6.1 Servicing brake calipers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.2 Removing and installing piston for rear brake caliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7 Bleeding brake system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
7.1 Bleeding sequence for vehicles with Electronic Stabilisation Program (ESP) . . . . . . . . . . 110
7.2 Changing brake fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
8 Brake servo/ brake master cylinder - exploded view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
9 Removing and installing brake master cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
9.1 Removing and installing brake master cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
10 Removing and installing brake servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
10.1 Removing and installing brake servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
11 Vacuum pumps for brake servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
11.1 Vacuum pump - exploded view (3.0 ltr TDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
11.2 Removing and installing vacuum pump (3.0 ltr. TDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
11.3 Vacuum pump - exploded view (4.0 ltr TDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
11.4 Removing and installing vacuum pump (4.0 ltr. TDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
11.5 Vacuum pump - exploded view (4.2 ltr TDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
11.6 Removing and installing vacuum pump (4.2 ltr. TDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
11.7 Removing and installing vacuum pump (2.8 ltr. and 3.2 ltr. petrol engine) . . . . . . . . . . . . 131
Audi A8 2003 ➤
Brake system - Edition 03.2013
ii Contents

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
12 Electric vacuum pump for brakes V192 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
12.1 Vacuum pump for brakes V192 - exploded view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
12.2 Removing and installing vacuum pump for brakes V192 . . . . . . . . . . . . . . . . . . . . . . . . . . 133
12.3 Checking vacuum pump for brakes V192 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
12.4 Removing and installing brake servo pressure sensor G294 . . . . . . . . . . . . . . . . . . . . . . 136
12.5 Checking non-return valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
13 Brake hoses and brake lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
13.1 Routing of brake hoses/lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
13.2 Tightening torques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
14 Repairing brake lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
14.1 Flanging tool - exploded view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
14.2 Instructions for use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Audi A8 2003 ➤
Brake system - Edition 03.2013
Contents iii

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Audi A8 2003 ➤
Brake system - Edition 03.2013
iv Contents

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
00 – Technical data
1 Brakes, wear limits
(ARL003290; Edition 03.2013)
Brake system
Diagonally split dual-circuit braking system with ABS, EBPD, EDL, ASR, ESP, ECD and EPB
Front brakes
Brake caliper FNR
G60
(16”)
FNR G60
(16”) FNR 42 AL (17”) FNR 42 AL (18”) FNR 42 AL (18”)
Factory code (PR No.) 1LG 1LG 1LL, 1LM 1LJ, 1LK 1LJ,1)
Ventilated brake disc ∅ mm 321 323 360 385 385
Brake disc, thickness mm 30 30 34 36 36
Brake disc, wear limit mm 28 28 32 34 34
Brake caliper, piston ∅ mm 60 60 2 x 42 2 x 42 2 x 42
Brake pad thickness mm 20.3 20.3 20.43 20.43 20.43
Brake pad wear limit (in‐
cluding backplate and
damper plate)
mm 9 9 9 9 9
1) Special security vehicle
⇒ “1 Front brakes (PR 1LG) ”, page 38
⇒ “2 Front brakes (PR 1LJ, 1LL, 1LM, 1LK)”, page 46
Note
♦ When performing repair work on brakes, hairline cracks are
often found on the friction surface of the brake discs. Hairline
cracks up to a length of 10 mm do not present a technical
problem and do not justify a renewal of brake discs.
♦ Brake discs with cracks going all the way across the friction
surface must be renewed.
Ceramic front brakes
Brake caliper Brembo M6 Al
Factory code (PR
No.)
1LW
Ventilated brake
disc ∅ mm 380
Brake disc, thick‐
ness mm 38
Brake disc, wear
limit
The minimum thickness of the
brake disc is stamped onto the
brake disc hub as a wear limit
specification.
Brake caliper, 6
piston monoblock ∅ mm 2 x 32/ 36/ 38
Audi A8 2003 ➤
Brake system - Edition 03.2013
1. Brakes, wear limits 1

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Ceramic front brakes
Minimum pad
thickness (includ‐
ing backplate and
damper plate)
mm 9.5
⇒ “3 Ceramic front brakes (PR 1LW)”, page 54
Note
Depending on the version, the minimum weight of the brake disc
is stamped on the disc. The brake disc must then be additionally
weighed in order to assess the amount of wear. The disc must be
renewed when the minimum weight is reached. Brake discs
should always be renewed on both sides of the axle.
Note
Hairline cracks on the friction surfaces of ceramic brakes can be
caused during manufacturing and therefore already appear to
varying degrees when the brakes are new. Hairline cracks on the
friction surfaces do not justify a renewal of the ceramic brake
discs.
Rear brakes
Factory code (PR No.) 1KE
(16”) 1KW (17”) 1KY (18”) 1KY 2) 1KZ (18”)
Ventilated brake disc ∅
mm 280 310 335 356 335
Brake disc, thickness mm 22 22 22 28 22
Brake disc, wear limit mm 20 20 20 26 20
Brake caliper, piston ∅
mm 43 43 43 43 43
Brake pad thickness mm 17.45 17.45 17.45 17.45 17.45
Brake pad wear limit (in‐
cluding backplate) mm 8 8 8 8 8
2) Special security vehicle
⇒ “4 Rear brakes, electronic parking brake and handbrake
(EPB)”, page 65
Note
♦ When performing repair work on brakes, hairline cracks are
often found on the friction surface of the brake discs. Hairline
cracks up to a length of 10 mm do not present a technical
problem and do not justify a renewal of brake discs.
♦ Brake discs with cracks going all the way across the friction
surface must be renewed. ⇒ page 54
Ceramic rear brakes
Brake caliper TRW CII45 HE - DK
Factory code (PR
No.)
1KU
Audi A8 2003 ➤
Brake system - Edition 03.2013
2 Rep. gr.00 - Technical data

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Ceramic rear brakes
Ventilated brake
disc ∅ mm 356
Brake disc, thick‐
ness mm 28
Brake disc, wear
limit
The minimum thickness of the
brake disc is stamped onto the
brake disc hub as a wear limit
specification.
Brake caliper,
1 piston ∅ mm 45
Minimum pad
thickness (includ‐
ing backplate and
damper plate)
mm 9.0
⇒ “4 Rear brakes, electronic parking brake and handbrake
(EPB)”, page 65
Note
Depending on the version, the minimum weight of the brake disc
is stamped on the disc. The brake disc must then be additionally
weighed in order to assess the amount of wear. The disc must be
renewed when the minimum weight is reached. Brake discs
should always be renewed on both sides of the axle.
Note
Hairline cracks on the friction surfaces of ceramic brakes can be
caused during manufacturing and therefore already appear to
varying degrees when the brakes are new. Hairline cracks on the
friction surfaces do not justify a renewal of the ceramic brake
discs.
Audi A8 2003 ➤
Brake system - Edition 03.2013
1. Brakes, wear limits 3

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
2 Assessment of ceramic brake discs
1 - Cooling channel lands
2 - Friction layer
3 - Carrier material
2.1 Visible features of ceramic brake discs
Checking area of bolted connection on friction ring and brake disc
hub:
WARNING
The brake disc ring and the brake disc hub are bolted together
and must NOT be separated. Do NOT slacken the bolted con‐
nection on the brake disc hub.
Audi A8 2003 ➤
Brake system - Edition 03.2013
4 Rep. gr.00 - Technical data

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Due to the production process there already are relaxation cracks
(varying degrees) on the friction surface of the brake disc when it
is new.
Note
Relaxation cracks on a ceramic brake disc do not constitute a
technical problem.
The relaxation cracks may be clearly visible and vary in size.
2.2 Superficial cracks in cooling channel
lands
Superficial cracks in the cooling channel lands -arrow- are caused
during manufacturing.
Note
Superficial cracks in the cooling channel lands do not constitute
a technical problem on the ceramic brake discs.
2.3 Cracks in area of bolted connection on
ceramic brake discs
Checking area of bolted connection on friction ring and brake disc
hub:
WARNING
The brake disc ring and the brake disc hub are bolted together
and must NOT be separated. Do NOT slacken the bolted con‐
nection on the brake disc hub.
Ceramic brake discs must be renewed if there are cracks in the
area of the bolted connection of the brake disc hub extending into
the friction surface of the brake disc -arrows-. ⇒ page 54
The brake discs must be renewed on both sides of the axle if:
♦ renewal is necessary because of brake disc wear
♦ there has been a technical modification to the replacement
brake disc (indicated by changed part number).
Always renew brake discs on both sides of axle. ⇒ page 63
When doing so, always renew the brake pads on both sides of
the axle. ⇒ page 57
Audi A8 2003 ➤
Brake system - Edition 03.2013
2. Assessment of ceramic brake discs 5

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
2.4 Edge fractures
Edge fractures -arrow- are caused by mechanical damage to the
edges.
Permissible:
♦ max. width / depth = 2 mm
♦ max. length = 10 mm
♦ max. 3 edge fractures per brake disc
If any of the criteria listed above are exceeded, the brake disc
must be renewed. ⇒ page 54
Always renew brake discs on both sides of axle if:
♦ renewal is necessary because of brake disc wear
♦ there has been a technical modification to the replacement
brake disc (indicated by changed part number).
Always renew brake discs on both sides of axle. ⇒ page 63
When doing so, always renew the brake pads on both sides of
the axle. ⇒ page 57
2.5 Chipping on ceramic brake discs
Always renew ceramic brake discs if there is chipping (larger than
1 cm² -arrow-) on the friction surface.
Always renew brake discs on both sides of axle ⇒ page 54 if:
♦ renewal is necessary because of brake disc wear
♦ there has been a technical modification to the replacement
brake disc (indicated by changed part number).
Always renew brake discs on both sides of axle ⇒ page 63 .
When doing so, always renew the brake pads on both sides of
the vehicle ⇒ page 57 .
2.6 Cracks extending into cooling channels
Always renew ceramic brake discs if there is a crack extending
from the friction surface of the brake disc to the cooling channel
or through the cooling channel -arrow-. ⇒ page 54
Audi A8 2003 ➤
Brake system - Edition 03.2013
6 Rep. gr.00 - Technical data

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
3 Assessing degree of wear on ceramic
brake discs
⇒ “3.1 Wear assessment by checking thickness of brake disc”,
page 11
⇒ “3.2 Wear assessment according to wear indicators”,
page 11
⇒ “3.3 Wear assessment by weighing brake disc”, page 12
When minimum weight is stamped on hub of brake disc:
⇒ “3.4 Wear assessment by weighing brake disc”, page 13
WARNING
The brake disc ring and the brake disc hub are bolted together
and must NOT be separated. Do NOT slacken the bolted con‐
nection on the brake disc hub.
Checking area of bolted connection on friction ring and brake disc
hub:
Designation of ceramic brake disc on brake disc hub
Audi A8 2003 ➤
Brake system - Edition 03.2013
3. Assessing degree of wear on ceramic brake discs 7

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
1 - Direction of rotation
2 - Supplier
3 - Serial production number of
brake disc
4 - Audi part number
Note
The Audi part number of the brake
disc is an example and can vary de‐
pending on the vehicle type and
model
5 - Production date of brake
disc
6 - Permissible minimum thick‐
ness of brake disc
Note
The minimum permissible thickness
of the brake disc differs depending
on the type of vehicle.
7 - Weight of new brake disc
with brake disc hub
Checking area of bolted con‐
nection on friction ring and
brake disc hub:
WARNING
The brake disc ring and
the brake disc hub are
bolted together and must
NOT be separated. Do
NOT slacken the bolted
connection on the brake
disc hub.
Note
Depending on the version, the min‐
imum permissible weight for a used
brake disc is stamped on the brake
disc hub. The disc must be renewed
when the weight of the disc is less
than or equal to the indicated mini‐
mum weight. Always renew brake
discs on both sides of the axle.
Caution
If the minimum permissi‐
ble weight of the disc is
indicated on the hub of
the disc (“min. weight”),
the disc must be addi‐
tionally weighed to as‐
sess the amount of wear.
Audi A8 2003 ➤
Brake system - Edition 03.2013
8 Rep. gr.00 - Technical data

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Caution
Always install brake
discs of the same type on
both sides of one axle.
The brake disc must first be cleaned before assessing the degree
of wear as described below.
WARNING
Do NOT clean the brake disc with water or other fluids as this
will falsify the results.
Note
♦ The brake disc ventilation drillings must be completely free of
brake dust and dirt. Clear out carefully with a suitable tool if
necessary. Do not use force.
♦ Thoroughly blow out the brake discs with compressed air (in‐
cluding the area between the cooling channels and ventilation
drillings).
Caution
Always observe respiratory protection requirements when
cleaning brake discs or other parts of the brake system using
compressed air.
To assess the brake disc wear, proceed as follows:
♦ 1. Wear assessment by checking thickness of brake disc
♦ 2. Wear assessment according to wear indicators
1. Wear assessment by checking thickness of brake disc
⇒ page 11
Thickness of brake discs in permissible range → brake disc OK
Brake disc thickness in critical
range min. Th + 0.2 mm Value at or below limit
↓↓ ↓↓
Further wear assessment ac‐
cording to wear indicators Renew brake disc
↓↓ ----------
2. Wear assessment according to wear indicators
⇒ page 11
None of the six wear indicators fully worn out → brake disc OK
---------- One of the six wear indicators
fully worn out
--------- ↓↓
---------- Renew brake disc
Audi A8 2003 ➤
Brake system - Edition 03.2013
3. Assessing degree of wear on ceramic brake discs 9

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Note
Depending on the version, the minimum permissible weight for a
used brake disc is stamped on the brake disc hub. The disc must
be renewed when the weight of the disc is less than or equal to
the indicated minimum weight. Always renew brake discs on both
sides of the axle.
Caution
If the minimum permissible weight of the disc is indicated on
the hub of the disc (“min. weight”), the disc must be additionally
weighed to assess the amount of wear. The disc must be re‐
newed when the weight of the disc is less than or equal to the
indicated minimum weight.
Brake disc with minimum weight stamped on hub:
1. Wear assessment by checking thickness of brake disc (if
minimum weight is stamped on hub) ⇒ page 11
Thickness of brake discs in permissible range → brake disc OK
Brake disc thickness in critical
range min. Th + 0.05 mm Value at or below limit
↓↓ ↓↓
Further wear assessment ac‐
cording to wear indicators Renew brake disc
↓↓ ----------
2. Wear assessment according to wear indicators
⇒ page 11
None of the six wear indicators fully worn out → brake disc OK
---------- One of the six wear indicators
fully worn out
--------- ↓↓
---------- Weigh brake disc ⇒ page 13
---------- Minimum weight not reached
---------- ↓↓
---------- Brake disc OK
---------- Minimum weight reached
---------- ↓↓
---------- Renew brake disc
Always renew brake discs on both sides of axle if:
♦ the brake discs have to be renewed because of wear.
♦ there has been a technical modification to the replacement
brake disc (indicated by changed part number).
Audi A8 2003 ➤
Brake system - Edition 03.2013
10 Rep. gr.00 - Technical data

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
If one of the three wear limits defined below has been reached,
do NOT continue using the brake disc. The brake disc must be
renewed.
In this case, always renew the brake discs on both sides of the
axle.
When doing so, always renew the brake pads on both sides of
the axle.
3.1 Wear assessment by checking thick‐
ness of brake disc
Special tools and workshop equipment required
♦ Use a commercially available caliper gauge or micrometer
gauge.
The minimum permissible thickness of the brake disc is engraved
as “min.Th.” on the brake disc hub.
– Measure the brake disc thickness at three points round the
outside of the disc next to the individual wear indicators -x-.
Note
If the thickness is x = min. Th. + 0.2 mm, additionally check the
wear of the brake disc by inspecting the wear indicators
⇒ page 11 .
When minimum weight is stamped on hub of brake disc:
Note
♦ When minimum weight is stamped on hub of brake disc:
♦ If the thickness is x = min. Th. + 0.05 mm, additionally check
the wear of the brake disc by inspecting the wear indicators
⇒ page 11 .
All types of ceramic brake discs (continued):
If the thickness of the brake disc is less than or equal to the min‐
imum permissible thickness “min.Th.”, do NOT continue using the
brake disc. The brake disc must be renewed.
In this case, always renew the brake discs on both sides of the
axle.
When doing so, always renew the brake pads on both sides of
the axle.
3.2 Wear assessment according to wear in‐
dicators
Wear indicators are positioned at intervals of 120 degrees on the
friction surface of the brake disc.
Audi A8 2003 ➤
Brake system - Edition 03.2013
3. Assessing degree of wear on ceramic brake discs 11

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
The wear indicators -arrow- appear in a different colour.
There are three indicators on each side of the brake disc (front
and reverse side).
The wear of the indicators is visible as a dark, burnt out recess.
Do NOT continue using the brake disc if one of the six indicators
is completely burnt out. The brake disc must be renewed.
In this case, always renew the brake discs on both sides of the
axle.
When doing so, always renew the brake pads on both sides of
the axle.
Checking area of bolted connection on friction ring and brake disc
hub:
WARNING
The brake disc ring and the brake disc hub are bolted together
and must NOT be separated. Do NOT slacken the bolted con‐
nection on the brake disc hub.
3.3 Wear assessment by weighing brake
disc
Special tools and workshop equipment required
♦ Commercially available scales with a tolerance of ± 1 g
Procedure
– Remove front brake disc for weighing.
– Remove rear brake disc for weighing.
• The brake disc must be cleaned and dry before it is weighed.
Caution
Do NOT clean the brake disc with water or other fluids as this
will falsify the results.
Note
♦ The brake disc ventilation drillings must be completely free of
dirt. Clear out carefully with a suitable tool if necessary.
♦ Thoroughly blow out the brake discs with compressed air (in‐
cluding the area between the cooling channels and ventilation
drillings).
– Carefully place the clean brake disc on the scales.
The initial weight of the brake disc with disc brake hub is engraved
on the disc brake hub.
For this model, the following maximum values are specified for
brake disc weight loss:
♦ Front brake disc: Up to 120 g weight loss from initial weight of
new brake disc.
Audi A8 2003 ➤
Brake system - Edition 03.2013
12 Rep. gr.00 - Technical data

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
♦ Rear brake disc: Up to 120 g weight loss from initial weight of
new brake disc.
Note
If the weight loss is only 20 g within these limits, additionally check
the wear of the brake disc according to the wear indicators.
If the weight loss has reached or exceeded these limits, the brake
discs must be renewed. It is no longer permissible to use these
brake discs. The brake disc must be renewed.
Always renew brake discs on both sides of axle if:
♦ the brake discs have to be renewed because of wear.
♦ there has been a technical modification to the replacement
brake disc (indicated by changed part number).
In this case, always renew the brake discs on both sides of the
axle.
When doing so, always renew the brake pads on both sides of
the axle.
3.4 Wear assessment by weighing brake
disc
Brake disc with minimum weight stamped on hub:
Special tools and workshop equipment required
♦ Commercially available scales with a tolerance of ± 1 g
Procedure
– Remove front brake disc for weighing.
– Remove rear brake disc for weighing.
Note
Depending on the version, the minimum permissible weight for a
used brake disc is stamped on the brake disc hub. The disc must
be renewed when the weight of the disc is less than or equal to
the indicated minimum weight. Always renew brake discs on both
sides of the axle.
• The brake disc must be cleaned and dry before it is weighed.
Caution
Do NOT clean the brake disc with water or other fluids as this
will falsify the results.
Note
♦ The brake disc ventilation drillings must be completely free of
dirt. Clear out carefully with a suitable tool if necessary.
♦ Thoroughly blow out the brake discs with compressed air (in‐
cluding the area between the cooling channels and ventilation
drillings).
Audi A8 2003 ➤
Brake system - Edition 03.2013
3. Assessing degree of wear on ceramic brake discs 13

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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
– Carefully place the clean brake disc on the scales.
The disc must be renewed when the weight of the disc is less than
or equal to the indicated minimum weight. Always renew brake
discs on both sides of the axle.
Always renew brake discs on both sides of axle if:
♦ the brake discs have to be renewed because of wear.
♦ there has been a technical modification to the replacement
brake disc (indicated by changed part number).
In this case, always renew the brake discs on both sides of the
axle.
When doing so, always renew the brake pads on both sides of
the axle.
Audi A8 2003 ➤
Brake system - Edition 03.2013
14 Rep. gr.00 - Technical data