Warning: On models equipped with ABS, disconnect the battery before opening the hydraulic system and do not reconnect it until bleeding and filling the reserve tank with fluid is complete. If this is not done, air may enter the ABS hydraulic system, which will require specialized diagnostic equipment to remove - you will have to contact your dealer for help.
Note: Before starting the procedure, please read the warnings contained in the paragraphs 2 and 5 about the harmfulness of asbestos dust and brake fluid.
Removal
Note: New guide pin mounting bolts are required for installation.
1. Place chocks under the front wheels, engage the rear shift (or "P" in the case of an automatic transmission), raise the rear of the car and install safety supports (see Jacking up a car and installing safety supports). Remove the corresponding wheel. When removing the wheels, tighten one bolt into each hub so that the brake discs do not mix with the hub.
2. As described in paragraph 15, release the handbrake, then release the handbrake cable adjustment so as to obtain maximum slack in the cables.
3. Disconnect the handbrake cable end from the caliper operating lever, pull the cable casing out of the caliper housing.
4. To minimize fluid loss, place a polyethylene circle under the reserve tank cap, creating a hermetic seal (be careful not to damage the sensor). You can use a clamp to clamp the brake hose closer to the caliper.
5. Remove any dirt around the brake pipe connection to the caliper and unscrew the union nut. Carefully remove the pipe and tape the end to prevent dirt from getting into the system. Clean up any spilled fluid immediately.
6. Unscrew the caliper guide pin mounting bolts, holding the pins with a thin open-end wrench. Throw away the bolts - new ones are required for installation.
7. Remove the caliper from the mounting bracket and unscrew it from the brake hose tip. Plug the hose and the hole in the caliper to prevent dirt from getting in and fluid from spilling in vain. Immediately rinse off any soaked fluid with cold water. Remove the brake pads. Unscrew the bolts and remove the caliper mounting bracket.
Repair
Note: The handbrake mechanism of the caliper cannot be repaired. If the mechanism is faulty or fluid leaks through the seal of its lever, the entire caliper must be replaced.
8. After installing the support on the workbench, clean it, but do not inhale the dust, as it is harmful to health.
9. Remove the piston by turning it counterclockwise from the caliper with a screwdriver or a square bar, inserting it into the cutouts on the piston. If the piston rotates freely, but does not come out of the caliper anymore, it can be pulled out further by hand, since it is held in place only by the seal.
10. Using a blunt tool such as a plastic knife, remove the piston seal from the groove in the cylinder, being careful not to damage the cylinder itself.
11. Remove the guide bushings with covers from the caliper struts.
12. Inspect the caliper components as described in paragraph 10replace defective components with new ones (handbrake mechanism - disassemblable).
13. Make sure all components are clean and dry.
Fig. 9.13. Components of the rear brake caliper: 1. Self-locking bolt; 2. Support; 3. Bleeding nipple; 4. Cap; 5. Piston seal; 6. Piston; 7. Guide pin; 8. Dust cover; 9. Dust cover; 10. Caliper mounting bracket
14. Dip the piston and new piston seal into clean brake fluid. Lubricate the cylinder surface with it. Install the new piston seal into the cylinder groove and install the piston.
15. Install the new dust boot into the caliper groove. Carefully and evenly insert the piston into the cylinder with rotating movements. Screw the piston into the cylinder clockwise until it stops and install the dust boot into the piston groove.
16. Apply the grease supplied with the repair kit or a good quality high temperature brake grease or non-stick compound to the guide bushings. Install the bushings onto the caliper and install the new boots, fitting them into the groove on the caliper and bushings.
17. Before installation, fill the caliper with fresh brake fluid by loosening the bleed nipple and bleeding the cylinder until bubbles stop coming out of the nipple.
Installation
18. Install the caliper bracket and secure with new bolts, tightening them to the specified torque (Fig. 9.18). Install the brake pads as described in paragraph 5.
19. Wipe the brake pipe joint clean. Install the caliper onto the brake hose joint, screw it on and install the caliper onto the disc. Install the new guide pin mounting bolts, tightening them to the specified torque.
20. Remove the clamp from the brake hose or remove the plastic from under the reservoir cap.
21. Bleed the hydraulic system as described in paragraph 2. It may be enough to pump only one disturbed circuit.
22. Attach the cable end to the operating lever, securing it with the clamp and adjust the cable as described in paragraph 16.
23. Install the wheel, lower the vehicle and tighten the wheel bolts to the specified torque as described in Chapter 1A or 1B.
(The text is based on materials from the website: AudiManual.ru)