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.