Front brake locked up

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gsa102
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Front brake locked up

Post by gsa102 »

So I was racing HS yesterday, and the front brakes got hot and locked up about 13 miles in (50 minutes). I smelled the brakes a couple miles before as I passed the pits. Luckily, It stopped near a group of people and someone had a wrench to let the pressure off. The pads were thin to begin with and were pretty much gone at this point.

After that, I started to avoid using the front brake. About 5 miles further they locked again, and someone was there with a multi-tool and I let the pressure off again. I got to the pits, checked for pressure, and duct-taped the wrench to the crossbar pad. On I went but avoided using the front brake. I didn't have to mess with it again for the last lap. It felt like it was dragging a little, but that might have been my butt dragging :mrgreen: .

Anyone have this issue before with the stock brakes?

I tightened up the lever before the race and might have had it too tight. The first time I stopped, I loosened the lever back up, but then the brakes locked up again later. I am thinking the relief hole in the master cylinder is plugged up, not letting the pressure off. As soon as I let the pressure off, the calipers released, so they shouldn't be hanging up.

Any thoughts?

I will be getting a tool bag to carry some tools if I am going to race a 15 year old bike. The motor/traction was awesome but the forks were lacking.
This is my rifle, this is my gun, the YZ to go fast, the KDX is for fun!

96 KDX 200, 09 YZ 250
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Julien D
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Post by Julien D »

Had the same thing happen last time out. Like yours, my pads were very thin. I'm inclined to think the caliper pistons over-extended and got stuck.
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Post by Fletch »

Air in the system? Otherwise what ^ said.
Fletch
89 kdx 200 with 99 rm125 forks
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rbates9
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Post by rbates9 »

I had an issue with a wrong brake lever that held the master cylinder just off it's neutral position and it made the brakes drag after just a few minuets of riding. It might be the plunger is sticking in the master cylinder and not moving out all the way.
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scheckaet
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Post by scheckaet »

worn pin?
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gsa102
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Post by gsa102 »

>|<>QBB<
juliend wrote:Had the same thing happen last time out. Like yours, my pads were very thin. I'm inclined to think the caliper pistons over-extended and got stuck.
Possible. Especially with the thin pads allowing the heat to get back to the caliper. But I wouldnt think the caliper should hold pressure unless the release path is blocked.

I'm with rbates9, thinking it is a lever/master cylinder issue. I noticed the brakes dragging a little right after I adjusted the lever up the day before the race, but didn't pay it any mind. But when I adjusted the lever back they still hung up. So it is likely the master cylinder piston.

I washed the bike last night and bled the brakes with fresh fluid. Promptly got air in them - doh. Time to get a turkey baster to reverse bleed. I am going to dissasemble them tonight and clean and push the pistons back in to make sure they are moving freely. And pads are on order.
This is my rifle, this is my gun, the YZ to go fast, the KDX is for fun!

96 KDX 200, 09 YZ 250
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