rear brake caliper

I was trying to push the piston back into the caliper to make clearance for my new rotor and pads, but it won't budge. I used the clamp and broke it. I also drain the brake fluid out. That didn't help. I had no trouble with the front calipers.
What should I do?
Could the piston be rusted or dirty?
Is there a way I can take the piston out and clean it?
Buying a new caliper is the last thing I want to do

your doin it wrong bro. i had that same problem.
heres how its done:
see the top of the piston on the caliper, it has those 4 notches. get a set of needle nose plyers and hold two of those notches that are across from each other and turn. the rear caliper on a 240sx is threaded so it needs to be turned down like a nut and bolt set-up. don't worry about the preasure you put on it earlier with that clamp, i proably did nothing to those threads.

Damn Grn, never heard of that before, I've never done the rear brakes on a 240 before.
By the way Per151, I did a five lug conv on my S14 and I have the I think right side caliper sitting somewhere in my shelves, that and tons of other OEM stuff like seat belts, rear seats, whole wiring harness and ECU, etc. All these I pulled out cuz I can't use them with my project so might put them on e-bay soon.

haha yeah when i was changing my brake pads I was using a c-clamp to try and push the piston back in. i tightened that thing as much as i could and the piston wasn't budging. i finally checked the fsm and found out that it was threaded. this was the first caliper i had ever seen set up like that. when you are gripping the notches with the plyers, make sure you have a good grip on it when turning because the plyers can slip off and scratch the piston.... i did it a couple times. it also requires a bit of force to turn the piston, but it will turn.

Screwed brake pistons, thats a first, good thing I've swapped the Z32 calipers, will never have that problem, now if I can only finish the damn project before Sept.