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Audi ur-quattro - Rear Brake Calipers and Handbrake

The calipers fitted to the rear of the ur-quattro - except the very early two-part caliper - are self-adjusting. But it is necessary to assemble and fit them in a specific way in order to have a fully functional handbrake - the process is not intuitive.

The procedure described here is for removal of the calipers, partial dismantling, cleaning, replacement of the seals and finally refitting. Depending on the situation, only part of it may be required.

Note that a seal kit will rebuild both calipers but a guide pin boot kit (recommended) only rebuilds one side. One reason for recommending guide pin boot kits is that replacement bolts (one use only) come with the kits - they do not come in seal kits, though they do come with new pads - at least from Audi. New seals should be soaked in brake fluid for at least 24 hours before starting.

Procedure:

• Use DoT 4 specification brake fluid
• Loosen the rear wheel bolts
• Jack up the rear of the car and place it on axle stands with the handbrake on
• Remove the roadwheels
• Release the handbrake - IT MUST NOT BE TOUCHED AGAIN UNTIL THE PROCEDURE IS COMPLETE.
• Loosen the handbrake adjustment. This is located above the exhaust and prop shaft under the centre of the car. A long extension with a deep 10mm socket is essential. There may be a locknut fitted to hold the adjustment in place - this has to be removed before the adjustment is disturbed. Because of rust, this may be difficult to discern. Shearing the actuator rod requires expen$ive repairs.
• Remove the handbrake cables from the caliper levers. A large screwdriver and heavy pliers are usually required.
• Remove the spring clip holding the outer of the handbrake Bowden cable to the caliper, noting its orientation.
• Remove the cable from the caliper. The boot stays on the cable. If the outer of the Bowden cable is rusted to the caliper, a gentle tap with a small hammer on a very fine (ca. 2mm) pin drift inserted from the caliper side will loosen it.
• Remove the caliper from the frame. This usually requires a thin 15mm or 17mm spanner to hold the guide pin and a 13mm ring to remove the guide pin bolt. The weight of the caliper should not be carried by the flexible hose - use stiff wire to hook it to the strut spring.
• Clamp the flexible hose close to the caliper. Halfords sell an excellent brake line clamp.
• Using a wide-jawed (large adjustable) or 14mm flare nut spanner, loosen the flexible hose at the caliper end and rotate the caliper off the vehicle - beware brake fluid spillage.
• Roughly clean the caliper and clamp it in a Black and Decker Workmate or workshop vice with wooden packing pieces.
• Wind out the piston anticlockwise. Most calipers have two recesses in the piston's rim - a Draper 179 or ground-down Sealey cube are available from motor factors. Some calipers have a recessed 12mm Allen socket instead - this must be thoroughly cleaned out before use. Large waterpump pliers can be used in an emergency - take care to grip only the very end of the piston.
• Pull the piston out of the bore. It may be necessary to pull the boot out of the recess at the outer end of the piston and slide it down a little.
• Pull out and discard the old boot.
• Using a seal pick, pull out the seal located a little way down the bore.
• Clean the bore throughly using paper towels or kitchen roll.
• Clean the piston thoroughly. It may be necessary to use mild abrasives - plastic pan scourers or very fine glasspaper. Make all cleaning motions around the circumference of the piston, not linearly up and down it. If the cleaned piston has rust pits, it and the caliper must be discarded.
• Take the new seal out of the brake fluid it has soaked in and place it in position in the bore.
• Lubricate the bore and new seal with brake fluid.
• Fit the small end of the boot over the inner end of the piston and push it about 1cm up.
• Locate the other end of the boot in the recess around the rim of the bore, paying special attention to the rear of the caliper - it is hard to see the difference between success and failure.
• The piston is now more or less located in the mouth of the bore. Align it accurately and try to insert it - which traps the large end of the boot in the recess.
• Once the piston is located, rotate it gently clockwise while pushing. Do not use tools at this stage.
• The piston should now rotate easily to a fully home position - practically flush with the end of the bore. Wind it out again about 10mm.
• If fitting new guide pin boots (recommended), pull the guide pins out of the caliper carrier, clean them and their bores, regrease and replace with the new boots. Caliper guide pins are not available separately - if they are seriously worn (perhaps because an old boot has split and the grease has gone) then the caliper carrier must be replaced as a unit.
• Wind the caliper back onto the flexible hose and tighten it.
• Replace the handbrake cable, taking care to move the handbrake lever on the caliper as little as possible.
• Replace the spring clip.
• Open the bleed nipple.
• Wind the piston back to its fully retracted position and refit it to the carrier frame.
• Remove the brake hose clamp and bleed the brakes. This can only be done with both calipers fully assembled - either after both have been done, or completely one before the other.
• Using the footbrake, fully seat the pistons against the pads to the point where a gentle depression prevents the brake disc from being turned.
• Once both sides have been bled and seated, the handbrake adjuster should be turned to a point where one handbrake actuating lever just moves off its stop. Pushing it back to the stop should cause the other side to move off. Wind the adjustment back three turns and check that normal operation of the handbrake lever allows it to come up three clicks on the ratchet. Otherwise release and adjust.
• Replace the locknut, if fitted.
• Replace and loosely tighten the roadwheels.
• Lower the vehicle.
• Tighten the roadwheels
• Carefully road test the vehicle.

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