Hello,
I have a rear brake caliper for a 2008 Ninja 250R that will not push out the pistons so that the rear break will function. I cannot figure out if the pistons are stuck or if the master cylinder for the rear break is faulty. When I push down the foot brake I get nothing. No pressure, no resistance, and if I loosen the bleeder nut on the caliper no brake fluid comes through. Any help is much appreciated, thank you!

 

Fill your brake reservoir and bleed the brake. Fluid should come out the bleeder valve if there is any in the system.

That is a start... Look for leaks to figure out where the fluid went if none is in the reservoir. That is the first step. If something leaks fix it. If something is stuck, fix it.

 

Hello,
Thank you for your response. Upon receiving your post back I decided to check everything one last time to make absolutely sure it is the stuck piston and the brake fluid is not leaking anywhere. In fact, I was surprised to find that the master cylinder for the rear brake worked. I was between the issue either being the pistons or the master cylinder not pushing fluid through. That is not the case as the MC works great! So it is in fact the pistons in the caliper. Soooooooooo, I purchased piston pulling pliers from Amazon. They will hopefully help me to free the pistons, clean them, reinsert and accept fluid. Fingers crossed. Thank you for responding as it reminded me to triple check everything leading to that caliper to be 100% sure that the piston was the issue. Cheers!!

 

You can pop pistons by plugging the hose fitting hole, putting a grease fitting in the caliper bleed hole - if it fits right - then pumping grease into the caliper should the piston pliers not work. If it is twin piston you use a c-clamp to hold whichever piston starts moving first, to get the other going. I've done this with cars, forget if I've done it with bikes. Usually you can get enough pressure to push them out with the pedal or lever, but clearly yours wouldn't. I've heard of people using air pressure too, but the grease pump works slower, just barely popping them out when they go.

Yeah, the grease is a bit to clean up, but not that big a deal and you could put it in a small jar to use on stuff like axles.

 

So, here's a good question about that grease gun you mentioned. I saw that as an option in a few videos on youtube along with the compressed air option. My question is, let's say I can't get the pistons out with the removal tool, how do I clean the grease out of the caliper once I pop the pistons out. The video I saw didn't not mention that part of the clean-up process, and another video said that you don't want the grease and brake fluid to mix, because I'm sure that's bad. Thoughts? Thanks again for your assistance!!!

 

Wipe it out, then wash the part. You'll have to clean the part anyway before reassembling it. Brake cleaner will wash out any grease left. If your piston is stuck it is likely you will have to clean out some crud and probably scuff up the bore with some really fine sand paper or steel wool.

 

Sounds good! Thank you so much for the help. I will let you know how it goes! Cheers!

 

Well THAT WORKED!!! Thank you so much for the help. The grease popped them both right out and clean up was relatively easy. I appreciate your patience as I attempted to do this for the first time ever. Thanks again, and have a great weekend!!

 

No problem. I learned a lot of stuff from other riders in person and on line. I didn't realize it was a twin piston, if you ever have a problem where only one wants to come out you can put a C-clamp on the one that is moving to hold it while you break the other loose. Been there done that. I hope all goes well.