I've got a '98 4runner and I'm going to do a full rebuild of the brake calipers soon. I have the 199mm Tundra calipers to do the upgrade, got them from a junk yard some years ago and installed but I just put my regular 4runner calipers and rotors back on while I rebuild the Tundras and have them powder coated. Anyway, my question is with the pistons. I've removed them from the caliper and I was careful not to scratch or damage the outside surface where they fit against the inside cylinder of the caliper. Since these are older calipers with what I think are original pistons, there is some rust on the inside cup part of the pistons, some of it is flaking off a little and I'm wondering if I should do something about it? 1) Is it even worth worrying about this? 2) If I do try to address the rust and flaking what methods/products could I use? I think it could be cleaned out with a small wire wheel on a Dremel or drill, use a rust treatment, and then something on top to protect it from rusting more? I have the POR 15 products but I'm wondering since that stuff is a little thick, if it will somehow unbalance the pistons and cause problems when braking? Or would it be better to remove the loose stuff, hit it with some etch primer (or something with a rust preventer) and then some light coats of spray paint to seal it off?

Again, this is for the INSIDE of the pistons, not the mating surface. I'm just wondering if some rust and flaking on the inside of the pistons is something to take care of while they are out of the caliper, will leaving the rust eventually eat through the piston, and if refinishing is an option what methods/products can be used?

Thanks.

 

Rust on the inside of the pistons is nothing to worry about. That side is exposed to the weather and will rust. If you want you could clean them and paint them. It won't have any effect on the braking.

 

Thanks for the reply, I think while they are out I'll clean the rust the best I can and give it a couple coats of paint and hope for the best. Thanks again.