|Originally posted by Knight Rider:|
It could also be the brake hose that is collapsing. I would replace it along with the caliper.
To expand on this a little, a collapsed brake hose closes off the fluid inside and acts like a one-way valve. When you push the fluid to the caliper, the car stops......but when you let your foot up, the fluid can't get back through the hose, and the brake pads drag on the rotor. The hoses look normal from the outside, so if they are old, they are suspect.