If the rear breaks are disc brakes, you'll need a caliper rewind tool as the piston is on a thread. You can get a draper tool that has the various pins, check amazon for brake caliper rewind tool. There are pins that locate in the piston to lock in place and the tool has a brake pad shaped backplate to allow pressure and rotation to return the piston into the caliper, also you will need to loosen the resivoir lid to allow the fluid to flow back into the tank and relieve some of the pressure
Hope this Helps!
Graeme, January 2010