Facts:

Had a rear passenger stuck caliper on my 245 which I only discovered after wearing the outer pad down to metal and scoring the rotor.

Replaced both rear rotors with NOS ATEs. Driver's rear caliper was perfect. Pistons slid nice and easy when installing new pads, which set well and have a strong bite after.

Front brakes are perfect. Nice and even pad wear with a ton of life left across all 4 pads.

Issue is only the rear passenger caliper.

This car has the "anti-spin" differential.

I bled using a motive bleeder and have a firm pedal. MC was always full. Got all the air out as far as I can tell. Brakes overall are very responsive so I don't think it's a bleeding issue.


Problem:

I bought a rebuilt caliper from Advance Auto. The "Whatever" Brand as it turns out. Installation was fine, but silly me I didn't test piston travel before installation. After installing the "new" caliper, I had good brake operation above 20mph. As I would decelerate below that speed I would get a pronounced shuddering from the rear. I thought it might be the differential doing it's thing if there was a problem with the new caliper. Sure enough, when I went to check operation with the wheels off the driver's side bites great, but the new caliper has stuck pistons right out of the box. Then, I came here to read all about the problems with rebuilt calipers - particularly the rear - that I am now experiencing first hand.

Plan was to throw the new one on and rebuild the old one. But this is my daily driver and I need it for work day to day. So upon learning of the problem, I ordered another rebuilt caliper from AutoZone as there is an outlet next door to my office. It was actually more convenient for me than to go back to Advance on the warranty. And I figured I might get the Advance one unstuck and have a second spare (I have a few 240s).

This time I check the AutoZone caliper before install - which looked to be better quality - and it too has a stuck piston. I want to take the thing and throw it through the lobby window of AZ corporate headquarters. But, can't do that.

Question:

What can I do here? I got the Advance caliper pistons working somewhat with a few light bursts of compressed air and started working them back and forth. But they're SO tight and keep getting stuck! Same with the AZ one now.

I don't see the point of claiming under the warranty only to get yet another useless POS.

What can I do to rehabilitate these supposedly rebuilt calipers? Both have pistons that are easy enough to get to move with air, but pushing them back in is very hard and requires a c-clamp for part of the way. With new pads installed, I know I'll have to recess the pistons as far as possible to get a good fit, and I'm concerned this will only serve to stick the pistons again once back on the car.

The driver's side piston travel in comparison can be manipulated with mere hand pressure.

Thanks in advance for the help.