I cannot get the cylinder to retract on the rear . Tried c clamp will not move. Didn't have any problem on front.

 

If it is the rear, it would be easier to use the brake tool to rotate and push at the same time. You can also use a needle nose plier.

 

You MUST rotate the piston as it's compressed.

 

correct, you must rotate the caliber as you retract the rears; this is a part of the e-brake system. This is not unique to MINI but one of the systems used for e-brake on rear disks. You can do it 'by hand' but is usually easier if you have a tool.

Harbor freight sells a $6 tool and a $80 set
http://www.harborfreight.com/automot...kit-69053.html
http://www.harborfreight.com/automot...ool-68972.html

Outmotoring has something similar

Larger 'chain' auto part stores may loan you a tool as they often have tool loan programs.

B4 you break something you may want to review
https://www.northamericanmotoring.co...beginners.html

 

The $5 one from HF works great. Put the tool on a short 3/8 inch extension with a T handle or short ratchet. Hold the caliper in your left hand, push in on the piston (after you line up the right pins) and rotate clockwise....piece of cake.