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MC piston not stuck... not coming out... Help?


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So I'm attempting to rebuild my master cylinder, and I'm having a bit of an odd issue. After removing the lever and piston set screw, the piston is refusing to pop out of the bore. It'll move in just fine, if pushed, but won't travel farther forward than flush with the end of the bore. There's quite a bit of dried brake fluid around, as the seals are well beyond "leaky" but there doesn't appear to be much in the way of junk in the actual bore itself. I'm currently trying to push the piston in and clean as well as I can, but between holding it in and the awkward angle I'm not accomplishing much.


EDIT: Despite the low amount of fluid from the leaky seals, the brakes worked fine before I began. There is no rubber gunked up on anything, and the reservoir is clean, so I'm fairly certain that there is no junk in the system causing any issues.


Thoughts on how to remove it? I've read some about people forcing grease and air (5k psi) through the bleeder hole, but I'm working in my driveway here, so those aren't options for me.


Any help would be greatly appreciated!

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Maybe a silly question, but have you removed the circlip?



Unless I'm totally nuts, there's no circlip on the R11 master cylinder piston. Went to check, in case I missed it, but I don't see one, and Haynes doesn't mention it.

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Not circlip but there is a set screw. Did you remove that?



Yep, sure did. But thanks!


Covered an allen key with a cloth and tried to pry it out but was unsuccessful. Don't want to completely mangle it, as it'd be nice to just change the gaskets and put the original piston back in.

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I've always used an air compressor. If thats not an option, maybe pick up a can of spray duster (canned air) and try that. You don't need much, but you have to build some sort of pressure up behind the piston to pop it out of there.......and I do mean POP. Make sure to have your hand and or a rag there to catch it or you will be looking for it in the grass.

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Morning JaySc


As mentioned above compressed air usually works good.


BUT!!!!!-- before using compressed air I usually remove the master cylinder from the bike.


Brake fluid is VERY damaging to plastic panels & especially dash plastic or RID plastic so ANY brake fluid that remains in the cylinder bore or fittings can blow around & damage the bike's paint or plastic.


Cover everything but even then compressed air can blow the fluid where you don't want it.


I'm not sure if there is enough of a depression in the 1100 piston but if there is I usually use a pair of duck-bill snap ring pliers to grab ahold of the piston then work it out.


Just remember there is a small hole in the bottom of the master cylinder reservoir (take-up port) that will allow leakage (blow-back) up through the reservoir if you use compressed air into the outlet fitting.


If you don't want to remove the master cylinder (removal IS the safest way to work on it) & can't get a good hold of the piston, & don't want to use compressed air due to possible fluid spraying out all over the bike then maybe try a little heat on the master cylinder (low heat) as maybe that will allow the crud to soften enough to get the piston out by just working it in & out.


Added: or possibly remove the end banjo fitting then (maybe) reach in with a long rod & see if you can PUSH the piston out the other side.

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Got it out. Thanks for the compressed air recommendation! I went over to a family member's garage, and between the air and a tiny screwdriver we were able to get it out.


The bore was as shiny as new, so that was nice. I was worried that it may be pitted what with all of the leakage lately.


Thanks for all of the help! Brakes feel great, but my rear rotor is warped. Looks like I have another project.

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