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Right hand drive Audi ur-quattro
Clutch master cylinder replacement.

Audi parts required:

• 478 721 171 Master cylinder
• N 902 547 01 x2 Locking clevis pin retainer
• N 011 184 09 x10 Nut
• N 011 183 11 x2 Nut
• N 902 920 01 x4 Nut

Procedure:

• Open bonnet, locate small clutch fluid reservoir near wiper motor and unscrew from bracket.
• Remove lower panel from left footwell.
• Remove clevis pin from left end of brake actuator rod (N502 547 01 destroyed).
• Remove steering wheel (24mm at 40Nm).
• Remove stalks (optional - three small straight slot screws).
• Disconnect driver's seat heater, and seat belt switch if fitted.
• Remove seat locking bolt at front of runner (5mm Allen).
• Remove block and cover from seat runners - cross-head screws.
• Place newspaper in rear footwell - seat runners are greasy.
• Remove seat.
• Remove cladding from right footwell.
• Remove clevis pin from right end of brake actuator rod (N502 547 01 destroyed).
• Remove nuts and bolts securing lower section of steering column in splines - clamp bolt must be removed completely.
• Remove lower section of steering column.
• Unscrew accelerator cable holder from pedal frame.
• Remove accelerator pedal.
• Unbolt and lower pedal frame - note one nut on engine bay side of firewall hidden by loom.
• Disconnect lines from master cylinder.
• Unscrew master cylinder - see note below.
• Push master cylinder backwards and disengage actuator rod.
• Fit new master cylinder, adjusting so that full piston travel can be achieved - critical for bleeding.
• Clamp sections of steering column together during reassembly.
• Fit new locking nuts.
• Ensure indicator arm is centred when steering wheel is replaced.
• The clutch fluid reservoir frequently splits and can leak after remounting. Audi's replacement is very expensive - try motor cycle factors for replacements sold as brake fluid reservoirs, e.g., Kawasaki, BMW.

Unscrewing the clutch master cylinder is tricky. It is secured by two bolts inserted from the outside of the frame, with two 13mm non-captive nuts on the other end. There is insufficient room between the body of the master cylinder and the frame to get a 13mm wrench of any sort past the master cylinder and onto the lower nut. The trick is to slide a 13mm 1/4" drive socket on a short extension in from the rear (as viewed - actually from the front of the car). When replacing the nuts, a piece of Blu-Tack or even some thick grease will hold the nut in the socket so it can be placed.

Because the master cylinder is mounted at an angle, there is a chord of the cylinder that will not expell air up the fluid feed pipe naturally. For this reason it is vital that the piston travels the full length of the cylinder when the pedal is depressed - otherwise it will be impossible to bleed the system properly.

It is possible with care to remove the brake rod clevis pin retaining clips without apparent damage. However - this rod is a CRITICAL safety item and it is recommended that the old clips be destroyed during removal and new ones fitted.

This is a good time to check and grease the clutch pedal pivot and the over-centre spring.

There should be a long and fairly weak return spring on the brake pedal to ensure the brake lights switch off properly, but it is often missing and badly catalogued in ETKA. Part number is 322 721 191

A different procedure is required if the vehicle has factory air-conditioning fitted, because the evaporator blocks access to the left end of the brake actuator rod.

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Contact Phil Payne by email or use mobile/SMS 07833 654800