The tools I rented to turn back the caliper wouldn't fit. Don't know why. So I was able to turn it back by hand with pliers. It was fine, then I thought I heard a spring release/snap.The piston started to move outwards. This is my first time with read disc brakes, I opened the brake resevior to allow for fluid to back up. I was checking that when I heard the noise. I can retract the piston, but it just come out again. The Haynes manual states I should open the brake bleeder when retracting. I didn't. Am i looking at a new rear caliper?