anyone have this problem? rear brake mc pulling apart

3 replies to this topic
  • vet45

Posted July 26, 2011 - 02:18 PM


2009 yz450f . i have had this happen three times now, twice in the same day. the plunger/washer/circlip come out of the rear master cylinder while riding (still attached and dangling from the rear brake pedal).
thew first time i thought it was a fluke, hit a rock or something but twice last sunday suggests a problem. circlip seemed normal as did the groove it sits in. does anyone know of an issue that would cause this?

  • grayracer513

Posted July 26, 2011 - 03:35 PM


The only thing that comes to mind is that your brake fluid is overfilled and/or contaminated with water, but heat expanding the fluid to the extent that it would pop the clip out should at least cause some noticeable brake drag before that happened, I would think.

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  • vet45

Posted July 26, 2011 - 04:17 PM


thank you Greyracer, I was hoping you would have an opinion. perhaps your right (still hard to understand that heat could cause that to blow out). i bleed these brakes frequently as my (pro level) son has a tendency to boil the fluid alot. i know that both times this happened Sunday, i had filled the MC to the point that it overflowed when i dropped the rubber in. I assumed the rubber would compress if needed , didnt think i was overfilling. your thoughts?

  • grayracer513

Posted July 26, 2011 - 05:41 PM


If the top seal/bellows was the right shape when it went in, what you did sounds right.

The rider's not yanking the lever with his foot or something, is he?

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