Hey guys,

I just spent a lot of time cleaning, repainting, and rebuilding my front calipers (4-pot aluminum) ... when I took the pistons out to rebuild them, I noticed that while the pistons themselves were smooth around the edges, a number of the piston bores were pitted. However, I've not experienced any leak problems or noticable braking issues with this car except a very slight rear lockup bias, which I was assuming proper lubrication on the sliding pins and a rebuild all round would probably fix. But before I put these front calipers back on the car, I'd like to know about this pitting. It looks fairly random and even, all the way around, and almost looks like it was in the casting. I don't know what would have caused it since the pistons were not themselves scored or pitted - and the calipers are aluminum so it couldn't have been rust. A few (one or two) caliper bores did not look pitted, just a dull, non-glossy smoothness, but all the rest looked very similar.

The pitting is not very deep, but its visible. There was nothing I'd call scoring (deep lines, scratch marks, etc..) to indicate it was caused by particles or scratched from piston motion, either. I'd take a pic but they are reassembled already and that was a bitch (and messy) to do.

Anyways, since I just replaced the piston seals, the pistons all slid out easily, I've had no leaking problems, and I know the seals are good, is it safe to re-use these calipers? I really don't want to get a rebuild set, first of all since I just painted these and cleaning them to get them painted was a bitch, and second of all since I just spent a fair amount of money on the mazda rebuild kit for them anyway.

 

^^ bump

 

Go ahead and use them. If it's just minor, that shouldn't present a problem. The worst you could have is a slight leak, which I doubt, but they won't be unsafe and allow the fluid to blow out. Maybe the ptting is behind the seal area which wouldn't create any problems at all.
FYI-They will corrode from condensation, especially the lower pistons/bores.

 

Ok. Yeah I thought if the seal area wasn't messed up then mild pitting, as long as it was not harsh, deep, or sharp edged, should be fine since the piston seal is what retains the fluid anyway... the piston should technically not ever contact the bore -- at least in the fronts from what I understand. But yeah the pistons themselves were fine. A little rusty outside the seal edge, but perfectly clean behind it. I took a brass brush to it and cleaned it up a lot.

And yeah, the pitting is almost entirely behind the seal area, none where the seal actually fits. And I think it was more predominant on the lower ones, yeah. Makes sense.

Cool they should be going back on this week.