front brake caliper stuck...

I just changed the front brake pads on my 2001 yz250 because when I got it they were not working well. when I got the pads out they were in need of being changed, so I figured that was what was wrong. I pushed the calipers back to fit the new pads in, bled the lines and put the system back on the bike. now the brakes dont work at all, the calipers won't move. Is it broken or am I doing something wrong?

There was no need to bleed the brakes when you replaced pads. You have air in you brake system and it needs to be bled. You can pressure bleed or vacuum bleed the system. You can also bleed them by pumping the brake lever, holding it compressed and opening the bleeder screw on the caliper, but that method can be difficult due to the "slow fill master" cylinder. That method can also be difficult because the piston in the master cylinder is small, and one stroke of the lever will not move an entire brake line lengths worth of fluid and air down hill, and out at one time. You can remove the brake caliper with the brake line attached, and hold it above the master clyinder with the brake bleeder at 12 o'clock. Then bleed the brakes as you would with the lever pumping method. It's messy, but it will keep the air from traveling back up the brake line to the master cyliner with it mounted in the normal position.

If you are desperate, you could take the shortest piece of vacuum line possible, connect it to a vaccum nipple on a cars engine. Connect the other end to the bleeder on the caliper and open the bleeder. Start the car and let the vacuum do the bleeding for you. Of course you have to have the lid off of the master cylinder and keep it full as the car engine sucks it out. You can control the amount of fluid sucked out by shutting off the bleeder when you think it is bled.

I just tried the bleeding method you suggested. It didn’t work. I think the caliper must be shot. I may have pushed the pistons in too far when putting the new pads in. They just won’t move. Is there a possibility that I damaged them.

Your caliper is ok, your most likely not getting any fluid to move through the system. Another thing to check is the master cylinder reservoir. In the botom of it is the fluid feed hole that the brake fluid goes into the master cylinder bore. I have seen them clogged up with debris (deteriorated seals), and this can keep the master cylinder piston from getting any fluid when pumping the brakes. It's also possible you have a defective master cylider too. One other thing to check for is to make sure the piston in the master cyliner is returning all the way to the "rest" postion when you let go of the lever. I have seen dirt/sand build up behind it where the lever touches it, and it can't return all the way back. If this happens, the piston will not pull fluid into the bore of the master cylinder.


I'm having the exact same problem. I know for a fact that I bled all of the air out of the brake line. I have one piston that is stuck in the caliper and the other appears to work just fine.

I've tried pumping the break leaver to loosen the piston... no luck.

I tried compressed air in the line (air compressor)... no luck.

Whatever you do DO NOT tap ever so carefuly with a drift punch on the exterior of the piston. Don't ask me how I know but it will break the piston :banana:

I'll be following this thread very closely to see what people think will work to get the pistons un-stuck.

If he has a firm lever and the piston(s) won't move, then the piston(s) may be stuck/defective. I think he has no pressure on the lever. We need the o/p to chime in and let us know.

If indeed he did push the piston(s) in and they are stuck, then I think it would be from rust or debris built up on them or in the piston bores, and when he pushed them in they got stuck. Also if the pistons are made of some type of "bakelite", they may also be distorted and be out of round from age and heat and wedge themselves in tightly when they were pushed back in.

I tried compressed air in the line (air compressor)... no luck.

If you just stuck the nozzle in the hole, it might be worth rigging up a better sealed connection and trying again, maybe with some penetrating oil. I've had pistons come flying out like cannon shells, though, so be prepared (aim it at something deserving the impact!)

i have had a few brakes go weak and not work along with sticking. i had to blead the lines on one cuz a kid pulled the brake lever while the caliper was removed and brake stuck. i took a small water line and pushed the brake fluid back throught the brake to get all air out. it worked well might be something to try.

Damm i too getting this problem on my rear brake caliper on my little pit bike. First the pistons were stuck and fixed that and put them back , but they go on tight. So bled the brakes and nothing , and i got all the air out. !! Bought another whole rear brake assembly used and got the same problem. \

Any body think its worth it to just buy a new whole brake assembly ? its only $40 total.

Bumping this old thread

I have a rebuild kit for my 86 CR80 front brake. the piston is stuck. I was able to use a C-clamp to push the piston in but I need to get out out to put the seals in it. I can't get it to push out by pumping the brake up. I have the entire system off the bike now. (upper Master, brake line, Caliper)

How can I remove the piston from the caliper?

When a piston sitts in the same position for a long time and it is exposed to water and dirt a ring of rust appers right were the piston enters the seal or on the inside of the seal. Never push the piston into the caliper to make room for new pads without pushing them out one or two mm for inspection/cleaning. If it can be cleaned you may push it in. If a piston with a ring of rust that can not be wiped away are pushed into the caliper you are asking for a jam. A ring of rust I have suxsessfully sanded down with 1200 sandpaper on an old car, BUT I WOULD NEVER REUSE A PISTON WITH THAT PROBLEM ON MY BIKE!

As for getting the piston out airpressure is the way to go. I once made a sealed hose system with a oneway valve (from a tiretube) to blow a carpiston out. Watch out it will come like a bullit:)

It was jammed before I pulled it off the bike. I hoped that using a clamp to push it in would break it loose a bit so I could pump it back out, but no dice so far. Getting new parts for this bike isn't the easiest proposition. So I'll have to clean up/reuse it once it's apart.

+1 on the air compressor idea- and he's not kidding about the piston potentially firing out like a bullet. You're essentially making an air cannon and it'll blow out with a ton of energy. Make sure it's going to hit something it can't ricochet off of or destroy.

Otherwise, you're gonna be drilling and tapping the piston so you can use a puller.

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