Stuck rear caliper (16v disc brakes)

[nlowe79 at gmail.com (Nate Lowe)]

So I went out to replace the brake pads on my '79 today (full 16v brake
conversion) and I got the front pads on fine with no problems (except a
cheap ass 13mm socket that broke removing the first caliper).

The rear pads were a different story. Or to be more precise, the driver's
side rear pads (I didn't even try the passenger side since I couldn't get
the driver's side on). When I got the caliper bolts removed, the caliper was
still tight on the pads and was hard to pull off. Then, when I tried to push
the piston back into the caliper with a 4" C-clamp, it would not budge. I've
heard of the brake cable sticking on 16v's (I think) so I removed the spring
that holds tension on it and tried to manually push it back thinking that
would help. No dice.

So the question I have is if this is a common problem and what steps should
I take to fix it?

Oh, and a bit of info, all the pads seemed to still have about 1/2 life left
in them even though my braking performance has noticably decreased. The car
still stops reliably, but not with the "bite" it had before. Maybe the rear
calipers aren't working at all right now?