There are a number of issues that can cause overheating disc brakes. Disc brakes, when released, separate from the disc by the action of the rotor moving between them (since no rotor is perfectly true, there is a small about of wobble and it pushes the pads away from the rotor surface). Things that can cause this to go wrong are:
- Caliper pistons that have rust rings that cause sticking. This most often will happen right after or shortly after replacing old, work out pads with new ones. Because the caliper piston was extended out farther with the worn pads, its surface may get rusty. This rust can cause sticking when the piston is pushed back into the bore with the new, thicker pads.
- Caliper slide bolts will rust and get sticky, not allowing the caliper to release properly and re-center itself on the rotor. What you often see here is that one pad (inner or outer) is totally worn out and the other seems normal.
- Rusty brake lines/caliper internals can cause restrictions in the flow of brake fluid and hold pressure after the brake pedal is released.
It is highly recommended that whenever you change your brake pads, you replace the caliper slide bolts use a new brake hardware kit when reinstalling. The additional cost is almost always saved in longer brake pad life, and fewer complications.