If your brake calipers have had multiple events where they’ve exceeded 450 degrees or any one event where they exceeded 500 degrees, many brake manufacturers recommend a rebuild. You also want to rebuild if you notice the dust boots have cracked or ripped like the ones in the photo above. Why take the risk of a caliper dragging because klag got past the boot or finding out too late that a seal has failed? It’s a relatively easy, but messy job. Have plenty of towels on hand to clean up. Remember: Brake fluid can ruin your paint. Do not grab a fender with a brake fluid soaked glove hand if working in a confined area. Instructions below are provided for illustration purposes only. As usual, refer to your workshop manual for guidance. Use at your own risk — no wagering.
Verify that you have all of the parts on hand before you begin. You will need a caliper rebuild kit and a bellows repair kit for each caliper. (On the first generation MINI, only the front calipers can be rebuilt.) You will also need replacement crush rings for the brake lines (2 per caliper), and since you will have to bleed the brakes, you might as well flush and replace all of the brake fluid. (Consider high temperature brake fluid if you track your car often.) It is critical that you not let the brake fluid reservoir run dry while you do this job. Modern brake systems are very difficult to purge if you allow air to get all the way to the reservoir. This would be an excellent time to change the brake pads and rotors as well. (This DIY only covers the caliper rebuild. See this old post for changing pads.) Expect this job to take 60-90 minutes the first time you do it.
1. Safely jack the car and remove the road wheels. Never work on a car supported only by a jack or one that is not fully supported by jack-stands.
2. Remove the caliper from the carrier. Note any cracking or damage to the bellows jackets of the caliper pins. This is a also sign the caliper has seen some serious heat cycling.
3. Note the type of brake pads in use. These Carbotech pads have a pin in the center that won’t allow the caliper to be slid off of the rotor until the piston is slightly retracted. If you pads are shot, just use a screw driver to carefully pry between the pad and the rotor to create clearance, but if you plan to reuse the pads, then carefully apply pressure directly to the piston to make room. Be careful to not damage the surface of the piston. Notice also the Brake Caliper Temperature Strips. This is a great way to keep track of the max temperature sustained by the caliper.
4. Hang the caliper so the weight is not supported solely by the brake line.
5. With the caliper off, inspect the rotor for excessive checking, cracking, or deep grooves. Replace as necessary.
6. With the pads removed, briefly reattach the caliper to the carrier. Wearing gloves, put down plenty of towels to absorb any spilled brake fluid and have a sandwich bag and zip-tie handy. Use a socket wrench to loosen the banjo bolt and catch dripping fluid into the sandwich bag. Place the bag over the end of the brake line and secure with the zip-tie. You have about 30 minutes before gravity will fill the bag. If you do not expose the fluid to air or grime, you can recycle it (well long enough to put it back and purge it when you do the pressure bleed later.)
7. Carefully empty any remaining fluid from the caliper and inspect the dust boot. If it looks like this one, replace and rebuild the caliper.
8. Once the boot is removed, check the piston for debris and damage before proceeding.
9. Place the caliper on a workbench and use an air pump to push out the piston. Place a towl under the piston to catch it as it comes out. Do not use excessive air-pressure or you will shoot the piston from the caliper. 20 lbs was enough to slowly release this one.
10. Inspect the piston and the chamber before proceeding. Remove the old seal and inspect it for damage. Ensure the new seal is the same size and thickness.
11. Once you’ve cleaned the piston and the caliper chamber, seat the new seal ring.
12. Push the new dust-boot so the end that fits into the groove on the caliper is exposed and can be fitted before the piston slides in to the chamber.
13. Engage the boot seat into the caliper and then slowly push the piston back into the caliper until the dust-boot engages in the slot at the far end.
14. Reattach the brake line using new crush rings. Use hangars to support the calipers again.
15. Reinstall/replace the brake pads.
16. If it hasn’t been contaminated, pour the brake fluid from the bag back into the brake reservoir, otherwise top off your reservoir with fresh fluid before bleeding. Be sure to top off before starting to work on the other side as you DO NOT want to allow air past the reservoir.
17. Bleed the brakes according to your workshop manual once booth calipers have been rebuilt.
18. Torque banjo bolts and caliper bolts according to workshop manual specs.
19. Once both calipers have been rebuilt and reattached, bleed the air from the brake system and replace fluid with new.