If I said reman calipers eat E36 M3, would I get an amen? Calipers arrived this AM, so I swapped the RH since that one was hanging up. Out of the box, the piston dust boot isn't seated to the caliper body.
Ok, I'll give 'em a little grace on that. Bleeds fine, no leaks, maybe it's all good. Except the park brake does not engage. The lever moves with the cable, but the piston does not clamp. berkeley you, caliper. Right where you eat. Oh well, mama's got somewhere to go, so it's staying on til next weekend.
So instead of happily boxing up my core, I started cleaning and disassembling the OE caliper to see what I was up against there. Torn dust boot on piston let some crud build up inside, and there was a good bit of aluminum oxide built up on the housing. A bit of careful scraping and a light hit with a soft wire cup got the housing cleaned up, so I moved on to getting the piston to retract.
Pro tip: instead of potentially damaging something by muscle-berkeleying the piston to retract, it's a better move to operate the park brake lever and push the piston out a little from where it's stuck. This gives you a little room to clean the piston, and reduces the chances of damaging the seal when you do run it in. I got everything working smoothly and ran the piston through full travel a few times before thinking I should take the piston out and inspect the internals.
bore and seal groove:
park brake side of piston:
sealing surface of piston (that's just discoloration, not pitting, I promise):
and piston seal:
If you look closely you can tell which way the seal was oriented in the bore.
I will buy new piston seal and dust boot, put it all back together, and R&R it next weekend so I can return the POS reman.