2000 Mustang rear brakes need help!

I am pretty much a shade tree mechanic, and to save a few bucks I am replacing my wifes brakes on her 2000 Mustang (not the cobra). The front went great but I can not get the cylinder in the rear caliper to retract so that the new pads will fit. I have tried everything to my knowledge. If anyone can help I would greatly appreciate it.

Thank you
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Your rear calipers have ABS, you need to use a $10 tool that can be bought at most part stores that wil twist the caliper back in not push it in like the fronts.

i just redid my front and rear brakes totally, the piston twists in. it was so funny, me and my dad couldnt figure it out i was gettin soo pist off. we ended up not using the tool cuz it wouldnt fit in the grooves, i ended up using a pair of needle nose pliers

Thank all of you. I have never seen this type of piston system before! I appreciate the help, it was driving me crazy.

Mark