ok,these calipers require a specail c clamp tool to compress the pistons in the rear calipers,this c clamp tool will actually turn and compress the piston at the same time,you should be able to purchase this tool at a parts store or a tool store like sears to do this repair.Below is some pictures of the caliper and tool,let me know if you need anything else Thanks Pete.
ASE Certified Technician
12 years GM diagnostic Technician/Mercedes Benz Technician