2013 yz250f front brake locking up

So was at a track yesterday and after doing a step up I went up off the track to talk to my buddies and randomly my front brake wouldn't release. So after I make it off the track and start heading back to my truck and had embarrassing wipe out when it completely locked up luckily the track owner came over and we bled the pressure off it through the bleeder and after that it worked great for quite a while and rode the smaller track they have. So I go back out on the big track and did a few laps I hit the same step up again and go up off the track and it locks up again. Ended up just taking the whole system off and riding without a front brake but has anyone else ever had this issue? Plan on getting rebuild kits for the master cylinder and the caliper and cleaning everything up really good, and the bike is completely stock still. Any help appreciated!!!

I'm no brake expert, but my rear brake is doing the same thing. I rebuilt the caliper, but it made no difference. It still drags a lot. I'm going to rebuild the master cylinder next. I'm suspicious that maybe the spring inside, has gotten weak and not pulling the fluid back as much as it should. Like I said, I'm not sure about this but the master cylinder is what I'm going to check next. Good luck.

Im definitely rebuilding both either way I don't risk anything when it comes to brakes especially the front one don't need to be mid air and it decide to lock up lol thanks man good luck let me know how it works!

Before you do all the rebuilding, completely flush your brake fluid and ride it.

Brake fluid can and will absorb moisture from the air. This moisture expands when hot (steam) and in a small closed system it will lock up your brakes when it expands. It cools down and seems to work fine until it reaches boiling point again

You must also have free play at the lever where it touches the master cylinder piston and the piston must fully extend to the snap ring. If there is no play or the piston fails to extend, the port in the master will not be open and as the fluid heats, it expands and applies the brake.

Before you do all the rebuilding, completely flush your brake fluid and ride it.

Brake fluid can and will absorb moisture from the air. This moisture expands when hot (steam) and in a small closed system it will lock up your brakes when it expands. It cools down and seems to work fine until it reaches boiling point again

 

 

Never ever known this

When the brake fluid has absorbed mositure, the moisture boils when the fluid gets hot and causes a spongy lever due to the pockets of gas compressing, but never causes the brake to lock on

 

Brakes locking on are caused by

 Pistons seized in caliper and so dont retract when lever released (note it is the seals which distort when the brake is applied, which pull the pistons back in, not the spring in the m/cyl lifting the fluid back up)

 No free play at the lever (as described by William1 above)

 The return port blocked in the m/cyl by a foreign object (have had this myself) resulting in the same issue as William1 describes above

Or an over full master cylinder.

Guygraham, would you want to wager that boiling brake fluid won't lock up a brake?

thanks everyone for the help I didn't get to post till now but I did rebuild both the other day and it fixed it thanks though for all the help!

I haven't rebuilt the master cylinder yet, but after your post, I'm motivated to do it. Thanks for the feedback

For like only 30 bucks to do it it's worth it

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