i'm changing the front brake pads and do the passenger side without any problems, then on the driver's side i get a surprise - the top piston on the inside is refusing to be pushed in. it moves a little, and i'm able to get it flush with the rotor and am able to push it in a bit, maybe a third of an inch or a little more, but at that point it locks and goes no further. so i can't put the new pad in.

i tried starting the engine to get power to the hydraulics, pumped the brake pedal a few times, nothing.

can anyone help?

get a c clamp and make it tight and it will push the piston in should work

Clamp and open the bleeder valve?

you can rent a tool from auto zone that opens them

got it to go with a screwdriver - not sure exactly how, but i spent 20 minutes at it, trying pushing in different combos of pistons, eventually it went, smooth like butter. i wish i knew what i did but i'm not really sure - wasn't about to experiment any further, i was just happy to get the pads in.