I'm traying to instal the back brakes and I can't puch back the caliper rod I did it with the front ones but the back is diferent there both disk can some one help :dunno:

You didn't tell us what the car was, but I would guess you are dealing with a car that has ratcheting calipers - and requires a tool to SCREW the caliper piston back into the bore.

FORCING IT BACK IN WILL RUIN IT......$$$$$$