08 450 front brake locked up

my son wrecked last night in a AMS arenacross. he got tangled with another rider. he got up and finished the race with a badly tweaked front end and a bent brake lever. I straightened out the front end and changed the brake lever. he went out for the heavyweight main and after one lap the the front brake started dragging locked up in the air over a triple. so he slowed down and tried to ride the bike off of the track but before he could get all the way through the whoops the wheel completely locked up. you could not move the lever at all. I took the bolt that holds the lever out and this released the brake. I put the lever back on and it seems to work fine. I checked the front rotor and it could be slightly bent but barely noticeable. the front wheel spins free. we are in Ohio so we really can't ride and he has another indoor race this weekend. and suggestions would be greatly appreciated

The adjuster at the front master cylinder that runs against the lever is set too tight. This will close off the fill port leading to the reservoir, and the heated fluid will be unable to back up into the reservoir as it expands.

Back off the adjuster until free travel is present, and reset according to the book.

08 450? Are you sure the rod that goes from the master cylinder to the lever is not put in backwards...I have seen this happen a couple times. The "ball" on the ends of the rod are different.

I only changed the lever, did not adjust or mess with in any way the plunger or any adjustment. I too have seen this happen before, it was on a 250f 08. we finally figured out the plunger was not fitting into the new oem brake lever. we drilled out the slot where the plunger fits in the new lever and it has worked right every since. but this is not the case with mine...

I took the bolt that holds the lever out and this released the brake.
This alone tells me that the fill port was closed off due to the M/C piston being pushed in too far. That can only be caused by incorrect adjustment or poor fit.

One thing that occurs to me is that you may have replaced the lever with one for an '07 or earlier model, which won't work correctly in the smaller '08 master.

thanks Gray,its the right lever for sure. but I think you are right I just have not had time to investigate today. at the very least I will take the lever apart and use the original part that attaches to the master cylinder. I even thought about taking the lever off our 08 250f and trying it.

Thanks Grayracer513 you are right. I bought an aftermarket lever for 08 YZ's if you hold it beside the oem lever you can not tell the difference. The cup or hole that the master cylinder plunger fits into was only half as deep as the oem lever. I drilled the hole deeper and this fixed the problem.

Thanks Grayracer513 you are right.
Basic hydraulic brakes, 101. :cool:

Whenever using replacement levers on an '08+ YZ450 or an '07+ YZ250F, be sure you use one appropriate for the year model.

People have this problem with ASV levers, and it stems from attempting to use the original Universal front brake lever (PN BLH01 for the C5 series) on an '07 or later YZ250F, '07 or later CRF250F/450F, or an '08 or later YZ450F master cylinder instead of the correct lever for that bike. The correct lever is BLH13 for the late YZ's and BLH15 for the late CRF's. Using the wrong lever can cause the master cylinder piston to be depressed far enough that it won't allow fluid to flow back up into the reservoir as it heats, resulting in a self locked brake.

Since the master cylinder is where the difference is, I would imagine this same thing would apply to any lever, including OEM.

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