14.1. Clean the caliper inner bore with Brake Clean and inspect the inner groove that the rubber brake seal sits in.
The inner bore is perfect with 90* edges and good tolerances.
The dust boot on this caliper was lifted and allowed moisture to corrode the inner bore and dust seal groove. This caused the caliper to ‘stick’ and bind, not allowing the caliper to release.
The hole in the piston was due to the corrosion in the caliper rubbing the piston and causing it to bind. This is an example of where the caliper and piston need to be replaced. The other caliper and piston are in great shape and can continue to be rebuilt.
A quick look shows the condition of the good caliper piston seal to the corroded piston and problematic caliper.
14.2. Coat the new seal with brake fluid and fill the caliper with new brake fluid. You do not have to fill the caliper all the way up, most of the fluid will drain out of it anyway. Make sure the entire inner bore is coated with fluid, especially where the seal fits. This will help lubricate the piston and allow it to slide in. Install the seal.
14.3. Install the dust boot on the piston so that the dust boot fits in the groove at the piston. Make sure the dust boot is put on and facing the correct way so that it will fit in the inner groove of the caliper. Lubricate the piston with brake fluid.
14.4. CAREFULLY press the piston back into the caliper BY HAND. Make sure the piston is straight as it will not go in if it is crooked. You can use a bar to SLOWLY and GENTLY press the piston in. Alternate 90* if the piston stops to alternate the angle of the piston so it does not jam. Eventually it will slide all the way in smoothly and nicely.
14.5 Tuck the dust boot back into the groove on the caliper. Use a flathead screwdriver and make sure the dust boot is all the way in the groove, otherwise it can corrode and cause problems in the future. The caliper is now rebuilt.