Brake problems

I am changing the back brakes on a 94 mustang. Easy enough to get off but I cannot seem to compress the caliper with my c-clamp. both sides are the same and I have put quite a bit of force to try and move it. I checked to make sure the e-brake is not engaged and seems to be functioning well. I have changed brakes before on trucks and am trying to do it the same way. Is there a trick to make the caliper compress. Thanks.

What I do, is with the caliper off, I put the old pad in front of the piston, and then put the c-clamp around the pad and the caliper and compress the piston. If this doesn't work (or you have already tried it) try taking the cap off of the master cylinder and then compressing the piston. Be careful to watch the fluid level (get a friend to watch it) so it doesn't overflow.

The piston screws back into the bore, not press. Most parts stores sell a tool to do this with, but it can be done just as easy with a pair of channel locks. It uses the rear calipers for the emergency brake, insted of hydrolic pressure it turns a screw which pushes the pad against the rotor.