Front brake staying tight

What would cause the front brake to stay tight? My buddy has a '06 WR450f and while riding the other day the front brake started getting tight. We opened the bleed screw to relieve the pressure, but after awhile it would get tight again. Since then we took apart the caliper and cleaned it out, put everything back together, and bled the system. Still gets tight! Any ideas out there? Thanks in advance!

I would guess your problem is in the master cylinder end of the system. Relief valve (not familiar with the WR, but most are the same idea) in the MC isn't releasing pressure when the lever is released.

If he changed to an aftermarket lever that is not releasing the piston all the way, it could cause it to not allow the brakes to release all the way. Troy341

Will it get tight on it's own? I mean without using the brake. If it does you have water in it, could be the fluid has water, I even had a brake line (rubber) that had water soaked into the cloth fiber and would tighten the brake all on it's own.

Now if it only does it using the brake you most likely have a valving issue in the MC.

I guess there is one more thing, has this bike spent much time in the water? it is possible to have corrosion on the piston and it just doesn't release like it should at the caliper.

Edited by thumpharder

Probably contamination (air or water) in the brake fluid.

Pretty easy to take the whole front brake off the bike and on teh bench.... flush it out real well, inspect the fittings/hoses for any leaks, then top it off and bleed it with fresh brake fluid then reinstall it on the bike.

A few years ago mine locked up when I was coming down the mountain (from about 12k ft). Really becomes obvious when the brake fluid heats up (like coming downhill from 12k ft), air expands and water boils a lot more than brake fluid does, so the brakes bind up. Did what I said above, reinstalled, and haven't had a problem since.

might be a colapsed line also

Make sure the reservoir in not completely full, just to the top of the window.

Thanks for all the input. It started after he took it up to Bridgeport, Ca. (at about 7000'). We are going to inspect the master cylinder next. We'll get some new fluid also. Also, it was only getting tight after squeezing lever repeatedly. Could be water. Might also get a new brake line for it as well. Thank you for all the help and will post if we finally figure it out!

Well good luck and just really take your time clean it well, use only new fluid when putting it together,and let us know what you find.

Thanks. Talked to my buddy today and suggested we tear everything apart again, and clean the crap out of it!

Alright guys, we think we figured it out. Nothing special, just took apart the master cylinder and cleaned everything really good, put back together with new brake fluid, and it seems to be working fine. Bled the system like normal, and squeezed the lever about a 100 times (isn't sticking like it had been). Could have been some moisture in the system, who knows. Thanks for all the input!

Nice, always good when the simple works

Went out for a ride yesterday and no problems! Thanks for all the input and help guys!

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