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Discussion Starter · #1 ·
I got my front brake caliper disassembled and cleaned. The piston took a lot of work to get out, but I finally did. I noticed two spots on the piston where there was some pretty deep rust. I just ordered a new piston. I did try to put the old piston in just a little bit to see how easy it would be. The rust is very close to the open end, so I was not attempting to put the piston in enough to get to the rust spot. I used brake fluid to lubricate the piston, then tried to push it in using my hands. It would not budge. I tried twisting, then I tried a little bit of pressure from some vice grips. I did not really go at it with the vice grips, because it seemed like it should not take that much force to get it in. So how much pressure should it take to get the piston back in? Has anyone else had this issue? Is it possible that my piston or the hole in my caliper has deformed somehow? I am pretty sure everything was very clean.
 

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Did you clean the rust off before trying to slip it back in the bore of the caliper?

If not, the rust is making the piston not a perfect circle like the bore of the caliper.

You don't want to score or scratch the caliper bore, so don't try to force it.

Forcing it you could score the bore and cause a problem.



Once you get it squarely started it should slip in pretty easily if you have it lubed up with brake fluid.

Your new piston should slide in pretty easily.

Just be patient and clean everything very well before you reassemble. Do you have a rebuild kit for the caliper?



David
 

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If you're going to the expense of fitting a new piston are you also fitting a new seal?



These seals get a buildup of hardened crud in the groove behind them which needs to be scraped out before the new seal is installed.



This build up behind the old seal along with possible age hardening of the seal are likely what gave you trouble on the test assembly
 

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Discussion Starter · #5 ·
I did order a rebuild kit as well last night. I figured I did not want to take a short cut on my front brake.




When I tried to reinstall the piston, I took the seal out of the caliper and cleaned behind it. Since I will have a few days before I get the piston and rebuild kit, I guess I can take my time and clean the caliper even better. It looks clean to the eye, but a bit more cleaning cannot hurt. Would it be bad to use some 000 steel wool on the inside of the bore of the caliper? I would not think that would hurt anything, but of all the parts on the bike, that is the last one I want to mess up!
 

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Discussion Starter · #7 ·
IMO, no, it is not okay to use 000 on the caliper bore. If it is scored or corroded, it needs to be replaced. If you have pulled the seal, the seal needs to be replaced. You can carefully clean the piston with 0000, but if the rusting / corrosion is in the area that "works" against the seal, then the piston needs to be replaced. The working area on the piston is relative to the thickness of the pads. Here is a pic of what I started with. I intend to rebuild without new parts. I've made a jig to spin the piston on a drill for a polishing with 0000. Aside from the corrosion on the front end of the caliper, the bore only needs a good wiping. The seal will not be removed, although the area's where the seal seats into the caliper will be gently cleaned with a very fine nylon toothbrush. I'm using PB Blaster as my cleaning agent. If all works, and the brake moves freely, it's a "go". If not, then it's replace with a aftermarket caliper. IMO





Thanks for the info. It has been very helpful. My old piston has one spot that is rusted, and the rust went deep. So I knew right away that it had to be replaced. I did not see any rust or corrosion in the bore, I just thought the 000 would help clean any little bits out that might be stuck that I cannot see. I will stay away from that now. Basically, I am in a holding pattern now until next week when the new parts arrive.
 
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