Audi Workshop Service and Repair Manuals

Note:

Brake master cylinder and brake servo assemblies can be replaced separately.

• Brake servo
• ◆ Checking operation
• ‒ Floor brake pedal firmly several times with engine stopped to dissipate vacuum in unit
• ‒ Then hold brake pedal in applied position employing moderate force and start engine; if brake servo is operating properly, brake pedal will be felt to sag (servo action)

• ◆ On petrol engines, vacuum required is tapped at intake manifold or generated by vacuum pump for brake
  
• ◆ TDI engines are fitted with vacuum pump/tandem pump for vacuum generation => Page 47-50
• ◆ In the event of loud suction noise on braking, check position of inner bellows => Fig.1
• ◆ Separating from brake pedal
  => Page 46-73
• ◆ Removing and installing
  => Page 47-84

• Cap
• ◆ With integrated float and warning contact for brake fluid level

• Brake fluid reservoir
• ◆ Can only be detached after removing brake master cylinder => Page 47-80
• ◆ Moisten with brake fluid and insert in sealing plug in brake master cylinder
• ◆ With integrated warning contact for brake fluid level (gradual introduction)
• ◆ Replacement of warning contact involves removing brake fluid reservoir
• Sealing plug
• Sealing plug
• ◆ Moisten with brake fluid and insert in brake master cylinder
• ◆ Press brake fluid reservoir into sealing plug
• Vacuum pipe
• ◆ With non-return valve
• ◆ Checking non-return valve => Fig.2

• Dust cap
• Bleed valve, 7 Nm
• Brake master cylinder
• ◆ Removing and installing
  => Page 47-80
• Locking bolt, 2 Nm
• ◆ For brake fluid reservoir
• ◆ Can only be screwed out after
  removing brake master cylinder
  => Page 47-81
• Nut, 20 Nm
• ◆ Self-locking
• ◆ Always replace after removing
• Sealing ring
• ◆ Replace
• Gasket
• ◆ For brake servo
• Nut, 28 Nm
• ◆ Self-locking
• ◆ Always replace after removing

→ Fig.1    Checking inner bellows at brake servo

• ‒ Remove driver's storage compartment.

=> General Body Repairs, Interior; Repair Group 68; Storage compartments/covers and trim panels; Removing driver's storage compartment

• ‒ Check that bellows have not slipped out of all-round groove as shown in Fig.
• ‒ Insertion of bellows involves removing brake pedal mounting bracket .

→ Fig.2    Checking non-return valve

• ◆ Non-return valve -A- must be open in direction of arrow and it must be possible to blow through it
• ◆ Non-return valve must remain closed in opposite direction and it must not be possible to blow through it

Note:

Pay attention to correct position on installation.