front brake drag

4 replies to this topic
  • 5valve

Posted May 03, 2005 - 08:42 AM


happened today, what could have gone wrong :D

brake lever gets stiff (after braking hard on some downhills), wheel gets quite blocked and after some standstill it loosens up
went on riding, blocked again, used water to cool down the brakes and fluid reservoair, I presumed the oil overheated, and voila, back to normal

the thing is, I changed original oil lines to braided ones and routed it CR style
had already done 2 rides- about 100 miles with a lot of front braking with no problems

of course I m using some no name DOT4 fluid, as said in the shop, DOT4 oils are all standard, seems not :naughty:

is it just oil weakened and finally broken down :naughty:

  • 5valve

Posted May 03, 2005 - 10:18 PM


I might have found the answer, still have to test it, not till friday

possible problem could be, since oil expands with heating and my reservoair level is (probably) too high, so the oil expands into lever and pads, forcing the lever to stiffen and pads to grab the disc
seems logic :) (now that I got partial answer on the web :D )

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  • RichBaker

Posted May 04, 2005 - 11:35 AM


Make sure the master cylinder piston is returning all the way. If it doesn't return all the way, the bleed hole will be blocked, resulting in a locked front brake....

  • Gadsen

Posted May 04, 2005 - 06:38 PM


Master cylinder must be at rest to release pressure from the replenishing port. If its not, the brakes being applied can create heat build up which can create pressure by heating up the fluid, which, in turn, applys more brake, which results in more heat, which means more pressure, which means more brake which means more heat... (see the snowball affect) and of course, your idea of the master being too full will give you the same results. Any contaminants in the fluid which can boil or expand at a greater rate than brake fluid will also do it.

  • 5valve

Posted May 05, 2005 - 06:49 AM


adjustment bolt on the brake lever was turned in to tight (no free play on the lever), of course It was my doing :) , so the expanding oil hit the bolt and applied constant brakes till it cooled down
that was the explanation i got from some mech, corrected the problem but didnt test it yet to confirm

(99 lever differs from past 2000 models wich are from 2 parts)

he also told me that oil level doesnt affect the expansion since the shrinking diaphraghm allows enough space for oil

hope thats it, and one tiny mystery more solved :D


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