Caliper piston question

[matthugie]

This is actually for my e36, but I'm in the process of rebuilding my OEM calipers and one front caliper and piston looks significantly worse than the other, and I'm wondering if it's an issue. In the first picture you can see the piston with the corroded top has some marks on it in the direction of piston movement. However, those marks appear to only be cosmetic as I can't feel them with the end of my finger or nail, and also the bore of the caliper looks perfect. Can (or should) I reuse this piston? The corrosion on the pad mating surface is pretty bad as is the interior of the piston, but I'm not sure either of those things would cause it to be unsafe. More brake parts cleaner and time with a wire wheel will probably clean it up some, but I don't think any reasonable amount of work will make it as clean as the other one. Thanks.

[jeffnhiscars]

Hi Matt. the concern with the piston/bore is whether they seal. As long as the bores are good and you clean the groove so the oring seats properly they hold work. My concern would be the corrosion on the surface that mates to the pad. If it's bad enough to prevent them from being square to each other it could cause uneven pad/rotor pressure. I can't imagine that being significant but I'd take some fine wet/dry on a piece of glass and smooth that mating surface. If you do take a wire wheel to it I'd suggest a brass wheel as it's less likely to mar the piston.

Having said all that have you priced exchange rebuilds ? I pay under $40 for my e30 calipers.

[matthugie]

Thanks Jeff. Given that I can't feel the scratches and that the caliper didn't seem to be leaking beforehand I think it will seal fine, but you do bring up a good point about the mating surface. I'll just clean it up and go with it.