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Old 12-19-2014, 11:46 PM   #1
Fireclimber OP
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Brembo brake lock up on my 525

I have had the front caliper lock up the last 2 rides after riding for several hours. Both times in wet conditions. The lever gets stiff and the front wheel starts to plow. I was able to back off the adjustment knob at the lever to free up the caliper and then the issue seemed to disipate and then return to normal. Pads do need to be changed so will get that done. Any idea what's going on?
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Old 12-19-2014, 11:53 PM   #2
Kai Ju
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You mentioned that adjusting the lever releases the locked brake.

Do you have any freeplay at the lever ?
If you don't, you might be covering up the compensating port hole that allows brake fluid to bleed back into the master cylinder reservoir once you release the brake. Which causes the brake to lock on due to the expanding brake fluid that is being heated up by the dragging brake.
The more it drags the hotter it gets. The hotter it gets, the more it expands. The more it expands, the more it drags.
You get the idea.
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Old 12-19-2014, 11:54 PM   #3
PeterW
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Quote:
Originally Posted by Fireclimber View Post
I have had the front caliper lock up the last 2 rides after riding for several hours. Both times in wet conditions. The lever gets stiff and the front wheel starts to plow. I was able to back off the adjustment knob at the lever to free up the caliper and then the issue seemed to disipate and then return to normal. Pads do need to be changed so will get that done. Any idea what's going on?
Changing the fluid won't hurt. Traces of water will do that, as will degrading brake lines. If you change the fluid, look at the old stuff, flecks of black in it, new lines.

It's also possible there's just not enough play at the master cylinder, there needs to be some slack there just to allow for expansion as the fluid heats up. Even without water in the system, it can be a bit of a juggle between enough slack, reach and good enough brakes on some bikes.

I'd suspect the reason it's happening in 'wet' conditions is that mud is building up on the brakes and the extra friction is heating things up - could be worse, if that is the reason it could also happen on the road on a long steep descent - that gets embarassing.

Pete
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Old 12-20-2014, 09:42 AM   #4
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Thanks gents. Brake line looks long enough. There is play in the lever. The bike is new to me and who knows when the last fluid change was so I will do that as well as look for degradation of the line. I have done brake bleeds before but nothing beyond that. Seems like I remember reading something about the cylinder can gum up. Should I look into that as well?
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Old 12-20-2014, 03:46 PM   #5
clapped_r6
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pull the caliper, take pads out and Very Carefully extend the pistons a little (TOO MUCH AND IT'S TROUBLE!!!)

you do NOT want them to pop out! just enough to remove the schmeg on the pistons. if there's funk there, they can't retract all the way and make too much heat, thus making the fluid hot.

then take an old toothbrush and remove and built up crud. push them back and reinstall.

it's also easy to overdo the amount of fluid in the master, make sure when they're bled that you can see a bubble in the master's window. Very easy to overdo the rear master, as there's not a lot of reserve fluid in there.
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Old 12-20-2014, 08:34 PM   #6
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It might be the wrong brake fluid that is causing the problem.
I believe the KTM should have DOT 3 or 4......if someone put DOT 5 in the system, it will not absorb moisture. The moisture will expand when the fluid is heated with use.
That can apply your brakes!

Change the fluid and start with the correct DOT rating.

Cheers
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