Greasing a number of caliper contact points is a necessary part of a quality brake job, but this isn't what I was referring to. A ring of dirt or corrosion builds up on the sealing surface of the piston inside the caliper, and in contact with the fluid. As the linings wear,
the piston moves out to self adjust. Eventually that corrosion works under the seal preventing the piston from releasing. Years ago the fix was to rebuild the caliper and clean or replace the piston, but today, rebuilt calipers are so inexpensive, we just replace them.
A less common problem is a pinched rubber brake hose. If the mechanic can catch the locking brake problem while it's occurring, he will open a bleeder screw. If the caliper releases, pressurized fluid is being trapped by the brake hose.
Wednesday, April 8th, 2009 AT 9:27 PM