So I'm trying to force the caliper piston into the side of the caliper with a C-Clamp, but it's being a pain in the ***. It's super hard to push it back in. I managed to push the driver side piston back into place and that was super easy, but the passenger side is super tough. I even bent the C-Clamp trying to do it. Any suggestions on how to push it back easier?

 

loosen the bleeder screw or the banjo bolt. Of course youll have to bleed the brakes after you get the piston pushed back in.

 

Did you remove the cap off brake fluid reservoir? If not follow what boosted said.