Safest way to clean Caliper Piston and Cylinder Bore Corrosion off?

Hi everyone,

I'm working on rebuilding a set of calipers on my own for the first time and I have some corrosion on the caliper piston and the cylinder bore. They were seized up so I pumped them out with a grease gun to free them up. I wouldn't even call it rust per say, it looks as if the brake fluid either dried up or got hot on the piston and this is kind of baked on by the looks of it. Here's a pic of one of the pistons:

Otherwise the pistons are in good shape and scratch, pitting, and nick free so I think these are definitely savable.

My concern is getting this glazed fluid off of the pistons and inside the bores. You can feel that it is a raised surface.

Obviously I don't want to do use anything abrasive that could scratch them so I'm looking for some tips here.

I've read that most people say a fine grit wet sandpaper is safe. What's the coarsest grit that I would want to use? 1000?

What about trying to heat them up and wipe down with brake cleaner? Could that help to "cook" the crud off?

Any other tips?

I would try brake cleaner, followed by fine metal polish. I would try to avoid sandpaper, at least at first.

Another option, if you think this is really caked on brake fluid residue, would be to soak both the piston and the caliper in cheapo brake fluid for a few days.

BoxheadTim wrote: I would try brake cleaner, followed by fine metal polish. I would try to avoid sandpaper, at least at first. Another option, if you think this is really caked on brake fluid residue, would be to soak both the piston and the caliper in cheapo brake fluid for a few days.

Yeah I think I'm going to get them started on a soak tonight.

I hadn't thought of metal polish but that's a good idea.

I've used this stuff on wheels before with good results and it says that it's non abrasive, would this be a good one to try?

Blue Magic Metal Polish

Looks to me like it'd be worth a try.

Aluminum or iron calipers? Boiling water might do it, brake fluid being miscible with water.

Do not heat brake cleaner is can be deadly in small amounts. Brake Cleaner=Phosgene Gas http://www.brewracingframes.com/id75.htm

Note--it states that a concentration of 4 parts/million can be sufficient to kill or harm-permanently. That's not very much. Yes, on occasion I'll use brake cleaner---but from now on, make damn sure there's no wet residual before welding. Bad thing is it can and will soak into castings.

Acetone and 1200 grit or finer paper

To clean off the old fluid I would use some paint remover. Safe for aluminum. Then some metal polish on the pistons. The cylinders are not that important as the piston rides on the rubber "O" ring for sealing so cylinder finish is not critical.

44Dwarf wrote: Do not heat brake cleaner is can be deadly in small amounts. Brake Cleaner=Phosgene Gas http://www.brewracingframes.com/id75.htm Note--it states that a concentration of 4 parts/million can be sufficient to kill or harm-permanently. That's not very much. Yes, on occasion I'll use brake cleaner---but from now on, make damn sure there's no wet residual before welding. Bad thing is it can and will soak into castings.

depends on the brake cleaner … if it's non-chlorinated, you're fine … if it's chlorine based and you weld after using and before it's 100% evaporated … you could easily die … Phosgene gas is the bi-product (hint: it's one of the gases that the Nazi's used in their extermination camps) … at best you'll create chlorine gas … which is also a killer

while the chlorine based brake cleaners seem to do a better job of cleaning, you should know what you're getting into before making the decision of which to buy

Hit it with every chemical you can find before you try anything abrasive - acetone is a good bet, if that won't remove it, what will?

When it comes time to use something abrasive, you'll want to use the finest sandpaper/emery cloth you have the patience for. 1200 grit is a good minimum.

I always used Emery Cloth (sp). Is it available any more ?

44Dwarf wrote: Do not heat brake cleaner is can be deadly in small amounts. Brake Cleaner=Phosgene Gas http://www.brewracingframes.com/id75.htm Note--it states that a concentration of 4 parts/million can be sufficient to kill or harm-permanently. That's not very much. Yes, on occasion I'll use brake cleaner---but from now on, make damn sure there's no wet residual before welding. Bad thing is it can and will soak into castings.

Thanks for the warning on this! I would have definitely wiped them down before applying heat, but you never know if all the residue would have been gone.

Since I didn't mention it before the calipers are aluminum.

I like the Acetone idea or paint remover too.

Would aircraft stripper be safe on the metal?

If that can't take it off I don't know what will.

In the past, I've used scotchbrite pads + brake cleaner to remove build-up from the pistons and bores. I've never had a problem with the results, but someone feel free to chime in if this is a bad idea for any reason.

I've always just used a wire wheel. The piston should be chromed or otherwise hardened. If a wire wheel hurts it, you got other problems.

0000 steel wool.

Lacquer thinner is my go to solvent.

I usually hit them on a spiral-sewn cottom buffing wheel charged with white rouge. They come out looking like they've been freshly chrome plated. Lacquer thinner and a soft brass brush on the calipers castings. New rubber and the correct grease, sparingly applied.

Thanks everyone. Between Acetone and a brass wire brush and some 0000 Steel Wool for good measure I got them cleaned up nicely and they are getting dropped off at the powdercoaters tomorrow.

Would you guys recommend just lubing the piston with some brake fluid, or should I lightly grease the pistons?

If greasing them is appropriate then what type of grease is safe on the seals?

No grease, brake fluid only.

Rebuild kits normally come with a packet of special grease. I believe its Kytox grease.

According to Wilwood

Link

"Using a very fine grit scratch pad, the insides of the bores can be smoothed out. If they appear to be in good condition just wipe them with lacquer thinner on a clean, lint-free rag."

Permatex makes a brake grease rated for pistons, comes in a little green tube at most parts stores. http://www.oreillyauto.com/site/c/detail/PER0/85188/N0448.oap?ck=Search_permatex+brake+grease_-1_4813&keyword=permatex+brake+grease