Break caliper piston not screwing,

[GT54145]

I am putting new brake pads and rotors on and everything worked fine for the front. Then when i went to compress the piston for the back it seems to just turn and not compress. Plus the pads looked liked they were not even worn. Could the caliper be bad? I bought refurbished ones for the back about a year ago and thought everything worked all right but maybe only the front were working.

[maxhopper]

I would say the calipers are not working properly. The fronts will do the majority of the stopping, but the rears should be worn.