Disc Brakes Audi A8 D3

DESCRIPTION & OPERATION

All models have self-adjusting front and rear disc brakes. Cable actuated parking brake mechanically activates the rear calipers.

Hydraulic system uses a tandem master cylinder with vacuum assist. Hydraulic system is diagonally split, left front and right rear wheels form one circuit and right front and left rear wheels form the other circuit. The brake pressure regulator has been deleted, as it's function has been replaced by ABS control module programming.

Depending on model year, A8 and S8 can be equipped with one of three different front brake assemblies. These different assemblies are

1. ATE FN3 Single Piston Caliper
2. HP-2 Dual-Piston Caliper (Steel or Aluminum Body)
3. Brembo 4-Piston Caliper

BLEEDING PROCEDURES

Without Electronic Stability Program

1. Ensure brake master cylinder reservoir is full. Connect hose to brake caliper bleed screw and insert other end of hose in a clear container 1/4 full of clean brake fluid. Bleed brake calipers in sequence. See «BRAKELINE BLEEDING SEQUENCE (WITHOUT ESP)»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes) table. BRAKELINE BLEEDING SEQUENCE (WITHOUT ESP) Application Sequence A8 & S8 RR, LR, RF & LF
2. About 1/2 pt. (200 cc) of brake fluid is expelled from each wheel when bleeding entire system. Before driving vehicle, depress brake pedal several times to ensure brakes are working correctly.

With Electronic Stability Program

Note. Electronic Stability hydraulic unit must be bleed using VAG 1551 or VAG 1552 scan tool.

Note. A positive pressure of 29 psi must be maintained to bleed hydraulic pump. Before beginning bleeding procedure, verify pressure bleeder setting.

1. Connect pressure bleeder US1116 or equivalent, to master cylinder reservoir. Connect hose to brake caliper bleed screw and insert other end of hose in a clear container 1/4 full of clean brake fluid. Bleed air from brake system in order. See «BRAKELINE BLEEDING SEQUENCE (WITH ESP)»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes) table.
2. Turn ignition off. Connect scan tool to Data Link Connector (DLC). DLC is located in center console behind ash tray. Bleeding of hydraulic unit is accomplished with scan tool in BASIC SETTINGS mode. Following scan tool instructions, navigate to BASIC SETTINGS mode. Connect hose to left front caliper bleeder screw, and insert other end of hose in a clear container 1/4 full of clean brake fluid.
3. Using scan tool command hydraulic pump on. Pump should run for 10 seconds. Repeat procedure until brake fluid runs clear with no air bubbles.

BRAKELINE BLEEDING SEQUENCE (WITH ESP)

BRAKELIGHT SWITCH

Working under dash, disconnect brake light switch harness connector. Remove brake light switch by turning brake switch 90 degrees to left. Pull plunger out as far as possible by hand. (Scheme 1) With hand press down on brake pedal, and guide switch into mounting bracket. Turn switch 90 degrees to right. Brake switch adjusts automatically. Connect brake light switch harness connector.

Scheme 1

PARKING BRAKE

Note. Adjust parking brake only if parking brake cable, rear brake pads or rear caliper have been replaced.

1. Place parking brake lever in released position. Check basic setting of parking brake. Raise and support vehicle. Using flat-bladed tool, press parking brake lever at rear brake caliper as illustrated. (Scheme 2) While holding parking brake lever on one side, observe parking brake lever on opposite caliper. If lever is pulled away from stop, adjust parking brake.
2. Depress brake pedal firmly at least once. Parking brake lever in rest position.
3. Locate parking brake adjustment nut near exhaust shield.
4. Using Parking Brake Adjuster (3343) or equivalent, loosen adjustment nut on pull-lever until parking brake levers are at stops. (Scheme 3)
5. Tighten nut on pull-lever enough that both levers move noticeably at the brake caliper (second technician required). Engage parking brake firmly at least once.
6. Adjust the adjustment nut on the pull-lever so that one lever at the brake caliper rises just before impact. Check basic setting again.

Scheme 2

Scheme 3

POWER BOOSTER PUSH ROD

Measure push rod length whenever power booster or master cylinder is replaced. Push rod length is measured from master cylinder mounting flange to center mounting hole in fork head. Measure distance "a". (Scheme 4) Adjust push rod length if not as specified. See POWER BOOSTER PUSH ROD LENGTH table.

POWER BOOSTER PUSH ROD LENGTH

Scheme 4

BRAKE PAD INDICATOR LIGHT

Instrument cluster warning lamp lights when relevant wear limit (3 mm) has been reached. To turn off light, replace front brake pads.

REMOVAL & INSTALLATION

CALIPER (FRONT)

Note. Brembo front caliper mounting bolts must be replaced during installation.

1. Raise and support vehicle. Remove wheels.
2. If replacing calipers, disconnect brakeline from caliper, and plug openings. If not replacing calipers, do not disconnect brake hoses. Do NOT allow calipers to hang by brake hoses.
3. Remove caliper mounting bolts. Remove caliper assembly from wheel bearing housing. To install, reverse removal procedure. Use NEW mounting bolts on Brembo calipers. On all calipers, tighten mounting bolts to specification. See «TORQUE SPECIFICATIONS»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes__torque-specifications) .
4. If necessary, bleed hydraulic brake system. See «BLEEDING BRAKE SYSTEM»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes) under BLEEDING BRAKE SYSTEM.

Scheme 5

Scheme 6

Scheme 7

HP2 Steel Caliper Bracket Retrofit

As of implementation of the combination sport suspension (8J x 18 wheel), the brake caliper housing of the front brake is equipped with an additional bracket (for all vehicles). If the 8J x 18 wheel is retrofitted and there is no bracket at the brake caliper housing, retrofit according to illustration. (Scheme 8)

Scheme 8

1. Raise and support vehicle. Remove wheels.
2. If replacing calipers, disconnect brakeline from caliper, and plug openings. If not replacing calipers, do not disconnect brake line. Hang caliper from body.
3. If removing rear brake calipers, disconnect parking brake cables.
4. Remove caliper mounting hex bolts. (Scheme 9) Remove caliper assembly from caliper carrier.
5. To install, reverse removal procedure. Tighten NEW caliper mounting hex bolts to specification. See «TORQUE SPECIFICATIONS»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes__torque-specifications).
6. If necessary, bleed hydraulic brake system. See «BLEEDING BRAKE SYSTEM»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes) under BLEEDING BRAKE SYSTEM.

Scheme 9

FRONT PADS (FN3)

Note. If re-using brake pads, mark them so that they can be installed in their original positions to prevent uneven braking.

Removal (FN3)

1. Raise and support vehicle. Remove front wheels.
2. Remove guide pin protective caps. (Scheme 38) Pry brake pad retaining spring out from brake caliper housing with a screwdriver and remove. Disconnect brake pad wear indicator harness connector (if equipped).
3. Remove both guide pins from brake caliper. Remove brake caliper housing and secure with wire so that the weight of the brake caliper does not stress or damage brake hose. Remove brake pads from brake caliper housing.

Installation (FN3)

1. Before inserting new brake pads, press piston back into the cylinder with piston resetting tool. Before pressing the piston back, draw off brake fluid from the reservoir with a bleeder bottle. Otherwise if reservoir has been topped off, fluid will overflow and cause damage to finish.
2. Insert brake pad with retaining spring in brake caliper housing. Remove protective foil on backing plate of outer brake pad. Install outer brake pad on brake carrier.
3. Secure brake caliper to brake carrier with both guide pins and tighten to specification. See «TORQUE SPECIFICATIONS»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes__torque-specifications) .
4. Retaining spring must be pressed under brake carrier after it is inserted in both holes. If the spring is improperly installed, the brake caliper cannot adjust to compensate for wear on the outer brake pad. This will cause the brake pedal travel to increase.
5. Connect brake pad wear indicator harness connector (if equipped). After brake pad change, firmly depress brake pedal several times with vehicle stationary so that the brake pads are properly seated. Check brake fluid level, topping as necessary.

FRONT PADS (HP2, ALUMINUM CALIPER)

Note. If re-using brake pads, mark them so that they can be installed in their original positions to prevent uneven braking.

Note. Pads on both sides of axle must always be replaced together. Pads are different on left and right side.

Scheme 10

Scheme 11

Scheme 12

Scheme 13

1. Raise and support vehicle. Remove wheels. Install one wheel bolt to secure brake disc.
2. Disconnect connector for brake pad wear indicator. (Scheme 10) Disengage connector from bracket using a screwdriver and simultaneously turn connector 90 degrees. Lift connector up and out and disengage wire.
3. Press upper and lower spring tensioner out of locking mechanism using pliers. Slide spring to side. (Scheme 11)
4. Press piston back into brake caliper housing. To do this, insert floating frame using a screwdriver and press powerfully outward.
5. Use screwdriver to press outer brake pads off brake caliper. (Scheme 12)
6. Press floating frame in direction of arrow until stop. (Scheme 13) Carefully press brake pads out of piston and remove brake caliper housing.

Scheme 14

1. Clean brake caliper housing thoroughly before installing new brake pads. Be especially careful to remove any residual adhesive foil, left by outer brake pads.
2. Insert lower and upper brake pads in piston. Be sure protrusions on backing plates are securely installed in brake piston. Do not damage protective caps when installing brake pads. (Scheme 14)
3. Press floating frame caliper outward until it contacts stop. (Scheme 15)
4. Install upper and lower tension (anti-rattle) springs in correct position. (Scheme 7)and (Scheme 11).
5. Remove wheel bolt from wheel hub. When installing wheels, ensure rim flange does not rest on brake caliper. This could push pads out of position.
6. After replacing brake pads and before moving vehicle, depress brake pedal several times firmly to properly seat brake pads in their normal operating position.

FRONT PADS (HP2, STEEL CALIPER

Note. If re-using brake pads, mark them so that they can be installed in their original positions to prevent uneven braking.

Removal (HP2, Steel Caliper)

1. Raise and support vehicle. Remove front wheels. Secure brake disk using a wheel bolt. Remove Torx bolts for the outer brake pads. (Scheme 6)and (Scheme 16).
2. Using a flat-bladed tool, press outboard piston back into brake caliper housing. Remove outer brake pad first, press brake pads off brake caliper.
3. Disconnect brake pad wear indicator harness connector, press spring and disconnect connector. To remove wire for brake pad wear indicator from bracket at brake caliper, carefully lift alignment tab slightly at lower part of connector using a flat-bladed tool, then turn 90 degrees toward left or right and remove from bracket.
4. Press floating frame powerfully in direction of arrow until stop. (Scheme 17) Carefully press brake pads out of piston using a flat-bladed tool and remove pads brake caliper housing.

Scheme 15

Scheme 16

Installation (HP2, Steel Caliper)

Note. Clean brake caliper housing thoroughly before installing new brake pads. Be especially careful to remove any residual adhesive foil, left by outer brake pads.

1. Insert/press in brake pad with wire for wear indicator in upper piston. Be careful not to damage protective caps when installing brake pads.
2. Insert lower brake pads in piston. Clip wires for brake pad wear indicator into bracket at brake caliper. Insert lower part of connector for brake pad wear indicator into bracket at brake caliper.
3. Press floating frame outward until stop. Remove protective foil on backing plates of outer brake pads. Ensure arrows on the brake pads point toward front of vehicle and in direction of brake disk rotation when driving forward. The springs (1) must be engaged in the gaps at brake caliper. (Scheme 18)
4. Install the NEW Torx bolts included in the repair kit into the floating frame and secure brake pads. (Scheme 16) Torque bolts to 18 ft. lbs. (25 N.m). Install wheels. Torque lug bolts to specification. See «TORQUE SPECIFICATIONS»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes__torque-specifications).
5. After replacing brake pads and before moving vehicle, always depress brake pedal several times firmly to properly seat brake pads in their normal operating position. Check brake fluid level, topping as necessary.

Scheme 17

FRONT PADS(BREMBO)

Note. If re-using brake pads, mark them so that they can be installed in their original positions to prevent uneven braking.

Removal (Brembo)

1. Raise and support vehicle. Remove front wheels. Secure brake disk using a wheel bolt.
2. Disconnect brake pad wear indicator harness connector, press spring for this and disconnect connector. (Scheme 19) To remove wire for brake pad wear indicator from bracket at brake caliper, carefully lift alignment tab slightly at lower part of connector using a screwdriver, then turn 90 degrees toward left or right and remove from bracket.
3. Remove circlips (1). (Scheme 20) Slide out locking pins (2) inward (arrow). Remove tension spring (3). Using a flat-bladed tool, carefully press inboard pistons back into caliper and remove pads brake caliper housing. Carefully remove inner brake pad. Repeat for outboard brake pad.

Scheme 18

Scheme 19

Installation (Brembo)

1. Before pushing back the piston, siphon some of the brake fluid out of the brake fluid reservoir. Otherwise, if reservoir has been topped off, fluid will overflow and cause damage.
2. Clean brake caliper housing thoroughly before installing new brake pads.
3. Carefully insert brake pads. Insert both circlips. Remove wheel bolt from wheel hub. Insert locking pins with tension spring. (Scheme 20)
4. Connect brake wear indicator harness connector. Connect connector to bracket.
5. When installing wheels, be sure rim flange does not rest on brake caliper.This could push brake pads out of position.
6. After brake pad change firmly depress brake pedal several times with vehicle stationary, so that the brake pads are properly seated. Check brake fluid level, topping as necessary.

Removal

1. Working under hood, remove plenum chamber cover. Attach bleeder hose of 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.
2. Remove mounting bolt (3) for brake fluid reservoir. (Scheme 21) Disconnect brake fluid level warning switch harness connector (2). Disconnect return hose (1) for clutch master cylinder (if equipped). On vehicles equipped with Electronic Stability Program (ESP), remove intake hose.
3. To remove brake fluid reservoir, press engagement strap downward and simultaneously pull brake fluid reservoir out of gasket.
4. Disconnect brake lines and seal with plugs. Remove mounting nuts for master cylinder. Carefully remove master cylinder from brake booster.

Scheme 20

Installation

To install, reverse removal procedure. Replace "O" ring between master cylinder and power booster. Before installing master cylinder, clean plenum chamber from any remaining brake fluid that may have escaped. Ensure push rod is properly centered in master cylinder. Lubricate rubber grommets between reservoir and master cylinder. Bleed brake system. See BLEEDING BRAKE SYSTEM .

PARKING BRAKE CABLES

Use following illustrations to aid in replacement of the parking brake cables. (Scheme 22)- (Scheme 24).

Scheme 21

Scheme 22

Scheme 23

PARKING BRAKE LEVER

Use following illustrations to aid in replacement of parking brake lever. (Scheme 25)- (Scheme 33).

Scheme 24

Scheme 25

Scheme 26

Scheme 27

Scheme 28

Scheme 29

Scheme 30

Scheme 31

Scheme 32

Scheme 33

Scheme 34

1. Pry off gap cover below steering column (arrows). (Scheme 34) Unscrew cover. Remove lower insulation mat.
2. Remove spring clip or clevis pin and disconnect pushrod from brake pedal assembly. (Scheme 35)
3. Working under hood, remove plenum chamber cover. Attach bleeder hose of 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.
4. Remove mounting bolt (3) for brake fluid reservoir. (Scheme 21) Disconnect brake fluid level warning switch harness connector (2). Disconnect return hose (1) for clutch master cylinder (if equipped). On vehicles equipped with ESP, remove intake hose. To remove brake fluid reservoir, press engagement strap downward and simultaneously pull brake fluid reservoir out of gasket.
5. Disconnect brake lines from master cylinder. Seal brake lines and master cylinder openings.
6. Remove fasteners holding power booster and master cylinder to firewall. Remove power booster and master cylinder together.

Before installing master cylinder, clean residual brake fluid from power booster. Ensure push rod is properly centered in master cylinder. To install, reverse removal procedure. Tighten fasteners to specification. See TORQUE SPECIFICATIONS . Adjust brake light switch. See BRAKELIGHT SWITCH under ADJUSTMENTS. Bleed brake system. See BLEEDING BRAKE SYSTEM .

REAR PADS

Note. Manufacturer recommends using NEW rear caliper-to-caliper carrier bolts during installation.

Raise and support vehicle. Remove rear wheels. Hold guide pin using open-end wrench while removing self-locking mounting bolt. (Scheme 36) Remove caliper and wire aside. DO NOT disconnect or damage hydraulic line. Remove brake pads from carrier.

Scheme 35

Scheme 36

1. Use Resetting Tool (VW 3272) to seat caliper piston fully into cylinder bore. (Scheme 37) Before pressing the piston back, draw off brake fluid from the reservoir with a bleeder bottle. Otherwise if reservoir has been topped off, fluid will overflow and cause damage to finish. Seat piston by turning special tool until piston is bottomed out in bore.
2. Install brake pads, note positioning of pad to caliper (tab on pad must fit into groove on caliper piston). If reusing old pads, ensure that pads are installed in original positions or braking may be uneven. Position caliper.
3. Install NEW caliper mounting bolts. With engine off, depress brake pedal several times to allow pads to move into operating position. Top off master cylinder reservoir as necessary. Adjust parking brake as necessary. See «PARKING BRAKE»(/audi/a8/d3-2002-2005/remont/mechanical-hydraulic/#disc-brakes__parking-brake) under ADJUSTMENTS.

Scheme 37

Disassembly & Reassembly

To overhaul caliper (Scheme 39)- (Scheme 41).

Scheme 38

Note. Apply a thin coat of brake cylinder paste G 052 150 A2, or equivalent, to brake cylinders, pistons and seals before reassembly. Also apply to to threads of caliper bleeder valve.

Scheme 39

Scheme 40

FRONT CALIPER (HP2, ALUMINUM CALIPER)

Scheme 41

Scheme 42

Scheme 43

1. Insert brake pad (b) in piston. Place a wooden board (a) into the recess of the caliper housing to catch the pistons so they are not damaged. (Scheme 43) Use compressed air to remove pistons. Only one piston can be pressed out at a time. Hold the other piston securely in brake caliper housing using piston resetting tool.
2. Removing piston seals using Wedge (3409). When removing, make sure that surface of cylinder is not damaged. (Scheme 48)
3. Install piston dust seals on piston. Insert lip of piston dust seal using Wedge (3409). Hold piston in front of caliper housing for this procedure. (Scheme 44)
4. Insert piston in hole by hand. Insert brake pad (a) in piston before inserting in brake caliper housing. (Scheme 45) Outer sealing lip of protective cap will then engage in piston groove.

FRONT CALIPER (HP2, STEEL CALIPER)

Scheme 44

Scheme 45

Scheme 46

Scheme 47

1. Insert brake pad (b) in piston. (Scheme 47) Place a wooden board (a) into the recess of the caliper housing to catch the pistons so they are not damaged. Only one piston can be pressed out at a time. Hold the other piston securely in brake caliper housing using piston resetting tool.
2. Remove sealing rings using Wedge (3409). (Scheme 48) NOTE: Apply a thin coat of brake cylinder paste G 052 150 A2, or equivalent, to brake cylinders, pistons and seals before reassembly. Also apply to to threads of caliper bleeder valve.
3. Install piston dust seal onto piston. (Scheme 46)
4. Insert inner sealing lip of piston dust seal using Wedge (3409). (Scheme 49) Hold piston in front of caliper housing for this procedure.
5. Insert piston in caliper bore by hand. Insert brake pad in piston before inserting in brake caliper housing. Outer sealing lip of protective cap will then engage in piston groove.

FRONT CALIPER (BREMBO)

Scheme 48

Scheme 49

Scheme 50

Scheme 51

1. Remove pads, and clean exterior surfaces.
2. Use air pressure to force piston from cylinder. Insert brake piston resetting tools (b) and (c) in piston. (Scheme 51) Place a wooden board (a) into the recess of the caliper housing to catch the pistons so they are not damaged. Only one piston can be pressed out at a time. Hold the other piston securely in brake caliper housing using piston resetting tool.
3. Remove piston dust seals using Wedge (3409). (Scheme 52) When removing, make sure that surface of brake caliper is not damaged.
4. Remove piston seals using Wedge (3409). (Scheme 53) When removing, make sure that surface of brake caliper is not damaged.

Cleaning & Inspection

Use alcohol or brake cleaning fluid to clean hydraulic chambers. Check cylinder bore and piston for corrosion and damage. Replace defective parts as necessary.

Note. Apply a thin coat of brake cylinder paste G 052 150 A2, or equivalent, to brake cylinders, pistons and seals before reassembly. Also apply to to threads of caliper bleeder valve.

Scheme 52

Scheme 53

Scheme 54

1. Install piston dust seal (1) on piston (2). Insert piston seal (3) in brake caliper. (Scheme 54)
2. Insert piston into hole by hand.Press brake piston past inner seal by hand.
3. Press protective cap 1.73" (44 mm) into brake caliper housing using piston resetting tool and Special Tool (3294/1). (Scheme 55)
4. Press protective cap 1.57" (40 mm) into brake caliper housing using piston resetting tool and Special Tool (3350/2). (Scheme 56)

Scheme 55

Scheme 56

1. Unscrew piston from brake caliper housing. (Scheme 58)
2. Remove dust seal from piston. Remove piston seal from rear caliper bore.

Use alcohol or brake parts cleaning fluid for cleaning purposes. Check cylinder bore and piston for wear and corrosion.

Note. Apply a thin coat of brake cylinder paste G 052 150 A2, or equivalent, to brake cylinders, pistons and seals before reassembly. Also apply to to threads of caliper bleeder valve.

Scheme 57

Scheme 58

1. Insert inner sealing lip of dust seal using Wedge (3409). Hold piston in front of caliper housing for this procedure. see scheme 59
2. Screw piston into brake caliper housing up to stop. (Scheme 58) Press powerfully on piston while screwing. Outer sealing lip of protective cap will then engage in piston groove.
3. Pre-bleeding brake caliper. Open bleeder valve and fill with brake fluid using standard bleeder bottle until brake fluid flows out of threaded hole (end of brake hose) without bubbles. see scheme 60 Close bleeder screw. Position brake caliper as shown during pre-bleed procedure.

MASTER CYLINDER

Manufacturer recommends replacement of master cylinder if defective.

VACUUM POWER BOOSTERS

Manufacturer recommends replacement of vacuum power booster if defective.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

DISC BRAKE SPECIFICATIONS

DISC BRAKE SPECIFICATIONS

See also:
• BRAKELINE BLEEDING SEQUENCE (WITHOUT ESP)
• TORQUE SPECIFICATIONS
• BRAKELIGHT SWITCH
• PARKING BRAKE