Brake System: Overview Audi S8 D3 facelift

General information

Brake fluid is hygroscopic, i.e. it has the capability to absorb water and moisture from the air.

Scheme 1

If water has been absorbed, the boiling point will drop, i.e., during high braking temperatures the brake fluid may develop steam bubbles and cause the brakes to fail.

Over time, brake fluid will darken in color. Dark-colored brake fluid does not specify anything about its quality. The coloring occurs through chemical reactions and can occur after a short time (several weeks), especially in vehicles with ABS.

Even the smallest amount on a seal or boot can cause the part to change and thereby affect the function of the brake system. The results of an unclean brake system first show themselves months later, causing increased repair costs, especially on vehicles with ABS.

Scheme 2

A = Boot - Original size

B = Boot - Swollen through contact with mineral oil

It is implied by the previously mentioned points that

Keep containers of brake fluid closed securely. This is to make sure that no oil, dirt or cleaning materials and no air moisture can enter the container.

Store containers of brake fluid away from oil (even hydraulic oil) and cleaning fluids to prevent an accidental mixing of both fluids or even filling the brake system with the wrong fluid.

Brake pedal, assembly overview

1. Lubricate all bearing and contact surfaces with grease OT no. G 000 450 02.

Scheme 3

1 - Hex head bolt

2 - Brake pedal mounting bracket

3 - Hex nut

1. Torque specification, 25 Nm

4 - Bold, Torx socket T45

1. Torque specification, 25 Nm

5 - Sleeve

6 - Brake pedal

1. Removing and installing --> «Brake pedal, removing and installing»(ref-289218-S13374911642008062700000)

7 - Socket head bolt

1. Torque specification, 9 Nm
2. The 3 hex bolts secure accelerator pedal module from other side

8 - Accelerator pedal

9 - Bold, Torx socket T45

1. Torque specification, 40 Nm

10 - Spacer sleeve

1. With adhesive seal

11 - Mounting bracket for pedal assembly

1. Illustration for automatic transmission

12 - Wheel hub support

1. For ball head of brake servo push rod

13 - Ball socket

14 - Insulating shell

Brake booster/brake master cylinder, assembly overview

Note. Use only new brake fluid. Observe information on brake fluid reservoir!

Scheme 4

1 - Bolt, Torx T45

1. Torque specification, 23 Nm

2 - Self-locking hex nut

1. Torque specification, 49 Nm

3 - Dual master brake cylinder

1. Cannot be serviced. Replace as complete unit if malfunctioning.
2. Removing and installing --> «Brake master cylinder, removing and installing»(ref-289218-S01438670422008062700000)

4 - Sealing plugs

1. Moisten with brake fluid and press into brake fluid reservoir

5 - Cap

6 - Brake fluid reservoir

7 - Vacuum hose

1. Insert into brake booster

8 - Sealing plugs

1. Connection for vacuum hose

9 - Tandem brake booster

1. Adjusting ball head --> «Adjusting ball head»(ref-289218-S08589712942009020900000)
2. On gasoline engines, vacuum is supplied from intake manifold.
3. Vehicles with a V6 gasoline engine and automatic transmission are equipped with a brake vacuum pump.
4. Functional check

1. With engine switched off, depress brake pedal firmly several times (to deplete vacuum in tool).
2. Depress and hold brake pedal with average foot pressure and start engine. If brake booster is working properly, pedal will be felt to give noticeably under foot (booster assistance becomes effective).
3. If malfunctioning: replace as complete unit.
4. With adhesive seal

1. Removing and installing --> «Brake booster, removing and installing»(ref-289218-S30489530762008062700000)

10 - Sealing ring

1. Replace

11 - Brake line

1. Torque specification, 24 Nm
2. Master brake cylinder/primary piston circuit to hydraulic control unit

12 - Dowel bolt

1. Torque specification, 10 Nm

13 - Brake line

1. Torque specification, 24 Nm
2. Master brake cylinder/secondary piston circuit to hydraulic unit

14 - Mounting bracket for pedal assembly

1. Removing and installing --> «Mounting bracket»(ref-289218-S05405156042008062700000)

15 - Hex nut

1. Torque specification, 25 Nm

16 - Bold, Torx socket T45

1. Torque specification, 25 Nm

Scheme 5

Left-hand drive vehicles

a = 184.4 mm ± 0.5 mm

Note. Reference surface - 1 - for adjustment dimension When measuring the ball head, it must be set at right angles to the surface of the brake booster. Measure to end of ball head without gasket installed.