back brake pads piston wont push in

kevin, July 2010

if calliper incoperates handbrake mechanism then piston has to be wound back! [but as you dont say make or model can't be more specific]

k, July 2010

front or rear? rear pistons need to be wound in with tool some are r/h thread some l/h.

wickham, July 2010

try using a G clamp over the sticking out piston,and caliper body undo the caliper bleed screw, a couple of flats(good luck because usually seized up ) now slowly wind up the clamp.fluid will ooze out
note
some newish car systems are now also threaded they can be right or left hand thread type basically this has been done to stop you messing .

wirecutterman, July 2010