Is there a trick to getting to piston to go back into the caliper?? I tried my old reliable C-clamp and cant seem to budge it...

 

The piston rides on a threaded stud that it uses for rapid expansion when the emergency brake is applied. To get it back into the caliper, you need to apply pressure to it's face while turning it clockwise. Several specialty tool vendors (Lisle, K-D) make a small tool for that purpose that fits a 3/8" extension. The tool has a variety of faces -- one of which will fit the grooves in your piston. Resist the urge to use pump pliers or the like to thread the piston back in. You don't want to scar the piston.