2004 Grand Prix GT2 Brake changing question

[angus young]

I recently tried , and failed to change the rear disc brakes on my 2004 Pontiax Grand Prix GT2 sedan. I was unsuccesful in pushing the cylinder back into the caliper, on both sides of the car. Is there some kind of trick to this? I used a big C clamp and psuhed back with an old brake shoe but it wouldn't budge, I have a hard time believing they are both frozen, the brakes seem to work fine, so I'm thinking there must be something I'm overlooking, any help is appreciated.
Thanks

[Langning]

I don't know if GM use the different design on your car. When I helped my brother-in-law with his Honda Accord, his rear-calipers were pushed back by turning the piston with a giant screwdriver. The piston is slotted in the Honda. On all of my other GM/Ford cars, they are hollowed which I used c-clamp to push.

[khsb]

i had the same problem with my 2006 grand prix but i use a pair needle nose pliers and turn the piston back in. Just make sure to line up the notch in the piston with the pad