I have been doing my own brakes on cars for years now, but on my Max it has like 4 grooves on the piston in the caliper on the rear. The front went back fine with a "C" clamp and then the rear seemed to need to be turned. Is this true? If so, does anyone have the tool needed for that?

 

Yes, it needs to be turned. I don't have the tool, but the 2x I've had to mess with it, I use needle nose pliers. stick it in perpendicular, slightly open, grip it in two opposite grooves, and twist.

 

yes, just like triple8sol said, just use a pair of needle nose pliers and twist, that's it.