Replacement Brake Caliper Pistons?

[LSB4Me]

Hi Everyone:

I have an 04 M3 with standard brakes and recently purchased a preowned front and rear ZCP/CSL brake kit. Prior to installation, I would like to rebuild the calipers as there is a good amount of rust visible inside the outer cavity of each caliper piston. (Note: I plan to attempt to clean the pistons, but tend to prefer fresh/clean parts when it comes to safety).

My question: Does anyone know where rear ZCP/CSL caliper pistons can be purchased?

It looks like Bimmerworld sells the rebuild kits (boots and seals) and replacement front pistons. This is great news … except they don’t have rear pistons and I’m not able to find them elsewhere.

Thanks in advance!

[cobra]

It's normal for the inside of the pistons to rust and doesn't affect them at all. They are thick.

[LSB4Me]

It's normal for the inside of the pistons to rust and doesn't affect them at all. They are thick.

Thanks for putting me at ease, Cobra. Much appreciated.

Any suggestions on what to use to clean them up a bit? PB Blaster and white vinegar come to mind.

Secondarily, the leading edge of the pistons shows a bit of tarnish as well so I’d like to clean these up a little at a minimum, if possible.

[cobra]

I would buff off the rust with some scotch brite or a wire brush and then put a thin layer of silicone grease to keep water from pooling and rusting further.

The important part is that the outside chromed portion is rust-free and that the dust boot is properly seated in the caliper and piston.

I think it's normal that the edge that rubs against the pads gets some tarnish. Less so on pads that come with anti-squealing material pre-installed like the stock Textar pads.

In the past I have actually sand blasted and painted caliper pistons on the inside to keep them from rusting. It worked pretty well. I guess the manufacturers only chrome the outside properly and don't care about how the middle part looks.