the caliper piston is not suppose to 'retract' it presses on the pad/rotor when you apply pressure and then that pressure stops when you take your foot off the pedal. the pads come off the rotor when there is no pressure.

 

the driver's side rear compresses when i step on the brake, but it doesnt go back down. i changed the caliper and its still happening. any ideas?

 

same thing happened to me..i had to expletive with it forever...it may seem like its locked on there..once u start drivin it its fine..hope this helps you