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front brake locking up???

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I went riding today with a buddy from work and had some issues with my front brake. I was in a field running around and doing wheelies and noticed my front end was sitting down low and wasn't coming up, well I did a small wheelie and as soon as the front tire came down I got thrown over the bars hard and fast. When I got up I picked up the bike and tried to roll it and the front brake was completely locked up and the lever was tight as hell. I had to crack the bleeder to relieve the pressure and then it was fine. After all that I rode it back to the truck to look the bike over and felt the brake caliper and it was super hot to the touch. It did it again a little later but I caught it before I endoed it again. When it locked up the second time I leaned it against a tree to cool off and it eventually freed up. I thought maybe the caliper piston was sticking which heated the shoes up till they just locked up but I'm not sure. Before it locked up the first time my buddy and I were flat tracking on an oval in the field and I was using the front brake pretty hard so i thought that had something to do with it but the second time it did it I was barely using the front brake. Anybody know what could be causing this and what I need to do to fix it?

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Maybe the brake fluid is boiling causing high pressure in the line which engages the brake? Just a guess. I don't really know a brake that well haha.

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Sounds like your have a pad hanging up. Check that the caliper can move around freely and that there is not a stuck piston. You might have debris in the caliper.

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I'm going to take it apart this week and see if I can figure out what is wrong with it. There was alot of mud in the caliper so it could have just not fully released. That doesn't explain why it released when it cooled down though so I don't know.

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was it hot out i have herd of stock lines warping in the heat and such and locking up the brakes.

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sounds like a front brake hose collapsed internally and causing the fluid to stay in the caliper. just a guess, but i'm pretty sure about it.

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sounds like a front brake hose collapsed internally and causing the fluid to stay in the caliper. just a guess, but i'm pretty sure about it.

And another cause for a brake to not release:The master cylinder piston is not returning all the way when you release the brake lever. The master cylinder piston must return far enough to uncover the port from the resorvoir. the adjustment between the lever and the piston could be adjusted wrong. Or a more likely cause on an older bike is what happened to me; pressure washing water got behind the master cylinder piston boot and caused corrossion that kept the piston from returning after releasing the lever.

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Does it get progressively worse as you ride? Chances are that means you've got air in teh line/slave cylinders that heats up and expands, locking up the brakes.

Personally I'd pull the calipers/MC off and get it on the bench. Clamp the MC in a vise and put the calipers in a catch pan and drain out all the old fluid. Clean everything up and flush/fill the thing with fresh brake fluid.

Took me about an hour to do it last time I did it, and mine needs it again.... Getting spongy :bonk:

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Old fluid will do this. One of my kids bikes locked up like that one time while were out in the middle of a trail. I adjusted the lever to get it to work and as soon as it cooled off he had no brakes, adjusted back and a little later it locked up again. I assumed it was the fluid, changed it as soon as i got home and it worked fine after that.

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I'm not sure what it is. I took it all apart and drained the fluid. The fluid in it seemed a little dark and the caliper pistons seemed really tight. Even with all the fluid out of the line and mc I still had to use a c-clamp to press the caliper pistons back in. I dont know how bikes are but I can usually press the caliper piston part of the way in with my fingers on my jeep. I am taking the whole thing to moto-x perts in Lafayette tomorrow to let them take a look at it. After doing a endo over the bars last weekend I want to make sure it's fixed right. http://moto-xperts.com/

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After Reading it all i just now see your an indiana rider !

Do any harescrambles ? Or participate in the Indiana riders Thread ?

And i dont think the caliper should be that stiff but i think that would just cause it to drag more than normal not really lock up as bad as you described.

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After Reading it all i just now see your an indiana rider !

Do any harescrambles ? Or participate in the Indiana riders Thread ?

I have never raced before but always kinda wanted to try it. I just got this bike about a month and a half ago and it's been about 8 years since I rode a dirt bike. I've had quads for the last 8 years so I'm still trying to get use to dirt bikes again. I think this bike is set up good for woods racing which is part of the reason why I got it but I still need alot of practice before I try racing it. I'm 30 years old too and tend to ride like I'm still 17 but my body doesn't recover like it use to!:bonk:

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... I still had to use a c-clamp to press the caliper pistons back in. I dont know how bikes are ...[/url]
I can't claim to have worked on all that many different makes/models but I've never done brakes on a car or m/c where the calipers wouldn't slide in easily when there wasn't fluid behind it. I suspect you've got either corrosion or deformation of some sort.

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Make sure the lever has freeplay.

If the adjuster is cranked in (or the lever bent), the master cylinder piston will close off the bleed port. As the fluid heats and expands, it has no place to bleed off to, therefore the caliper pistons move the pads to the disk.

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Well I took the brakes to Moto-Xperts (MXP) in Lafayette to have them take a look at them and they said that I probably had a bent rotor which caused the fluid to heat up and expand which caused the brakes to lock up. I didn't put much stock into what they were telling me because they havent even seen the bike to know for sure if that was the problem. When I was in the garage tonight trying to bleed the brakes I decided to jack up the bike and spin the front wheel and get a look at the rotor, and what do you know the rotor is wobbly as hell. I cant imagine that would be the reason the brakes would heat up but it makes sense to me now. When I was riding slower in the woods it must not have generated enough friction but as soon as I got out in the open field and was riding faster it heated up quickly even though I wasn't using the front brakes.

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doubt the rotor's causing the problem, that hydraulic system should soak that up, in other words, the pistons should retract when the wobble hits them, straighten the rotor out anyway, but, i'm still leaning towards the brake hose.

Edited by aakmetz

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Well I ordered a new rotor and pads, drained and flushed the fluid, pulled out the caliper pistons and cleaned them up real good. I bled the brakes but now I'm just waiting for the pads and rotor to come in so I can put them on and see how it does. I hope all that fixes the problem, I don't really feel like doing another endo over the bars!

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have you found the answer yet i am having the same problem with the same exact things that caused it

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Old fluid will do this. One of my kids bikes locked up like that one time while were out in the middle of a trail. I adjusted the lever to get it to work and as soon as it cooled off he had no brakes, adjusted back and a little later it locked up again. I assumed it was the fluid, changed it as soon as i got home and it worked fine after that.

There was probably a spec of crud in the master cylinder that was flushed out with the fluid change.

Dave

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