I had a brake caliper fail to release on me shortly after getting my car back from the shop (long story condensed is: took months to get done due to rust and lack of available parts from a wheel bearing failure and hub overheating). It's the caliper on the corner involved in the "long story" event. I initially wrote off the failure to old age/sitting unused/damage from the overheating event.
I tested the caliper on the car (after experiencing high wheel heat and brake smell from that corner), and the piston pressed out fine under hydraulic pressure, but was extremely tough to push back in. Based on other vehicles I've done, that sounds like a bad caliper to me. So, I pulled it apart and rebuilt it. Cleaned up beautifully, old parts all match to spec. During reassembly with the brand new rebuild kit & bench testing, I found that it's just as hard to push back in post rebuild as it was before. Maybe that's normal? The whole thing is to spec and has all fresh seals (although, the seal looks a lot thicker than the one that came out, but that could be age?) and was lubed per instructions.
So, the next step is to throw it on the car and see how it performs real world (at this point if it doesn't work I'll write this one off and trade it in on a re-man). While doing the install, rather than blindly assume everything was correct, I confirmed everything with the factory manual. It turns out that the lock and guide pins were swapped/in the wrong places! Now I'm wondering if that could have caused the caliper to not function properly under driving conditions? How exactly do the guide and lock pins function?
1995 Mitsubishi Eclipse GSX, very early in the production run so it has the rare more powerful rear brake configuration.