How to Replace a Rear Caliper on an Audi

1. Loosen the lug nuts for the wheel on the same corner as the caliper that is being replaced. Raise the rear of the vehicle with a floor jack and lower it securely onto jack stands. Finish removing the wheel and set it aside.
2. Remove the two bolts that hold the caliper on, using the appropriately sized socket. The size of the bolts will vary depending on the model. For example, the A4 uses a 13-mm bolt and a 15-mm nut to hold the caliper on.
3. Remove the brake line that goes to the caliper with a line wrench to avoid stripping the fitting. (A line wrench is an open ended wrench that goes further around the bolt than a standard open ended wrench, which minimizes the chances of stripping it.) Wipe up any brake fluid that was spilled when the brake line was removed.
4. Remove the caliper by sliding it off the rotor. The pads may stay on the rotor, fall off or stay with the caliper. Wipe off all the brake components and nearby components with brake cleaner and a clean rag before installing the new caliper.
5. Place the old pads (or new pads if you are installing new pads) into the new caliper. Slide the caliper onto the rotor. You may need to compress the caliper piston to allow enough clearance for the pads to go over the rotor. Use the special Audi piston retracting tool (see Resources 1) to retract the piston.
6. Install the new caliper with the caliper mounting bolts. Reinstall the brake line in the brake line hole. Bleed the brakes according the workshop manual for your specific Audi model. (This can be done with another person pressing on the brakes while you open the bleeder valve or using a vacuum bleeder.)