The rear brake pads on an Audi A6 use a caliper and rotor design for maximum clamping power. However, the downside to increased performance is increased wear and tear. You will need to check the brake pads on the A6 every six months for wear. When the pad material is down to 1/8 inch thick, you'll need to replace the pads.
Break loose the rear lug nuts on the A6. Turn them 1/4 turn counterclockwise with a tire wrench.
Raise the rear of the A6 onto jack stands. Use the rear jack point behind the boot to lift up on the car. Then, place jack stands on the rear jack supports in the rear of the vehicle. They are located on the side of the vehicle just behind the front doors on the bottom of the car. Then, lower the A6 onto the jack stands.
Remove the lug nuts, and pull the wheel off the rear hub.
Remove the upper and lower caliper mounting bolts with a socket wrench and 13mm socket. The rear calipers are unlike most calipers, because they have a nut that turns with the caliper bolts. To remove the mounting bolts, you'll need to hold this retaining nut still with a crescent wrench or open-end wrench while removing the mounting bolts.
Pull the caliper off the rotor. The pads should fall right off, because the A6 doesn't use a retainer on the rear caliper.
Retract the caliper piston with the caliper piston tool. Slide the tool over the grooves in the piston and turn the piston clockwise to retract the piston back into the caliper.
Slide the new pads into the caliper so that the curved end of the pad is facing inward toward the caliper.
Slide the caliper back over the rotor and put the brakes back together. Assembly is the reverse of disassembly.