rear brake master cylinder help?

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9/27/2017 2:11 PM

I have a rear brake master cylinder that seems to be having a problem that ive never had in my life before. When depressing the pedal the brake will stiffen up and work like normal 95% of the time, yet the other 5% it will stiffen up like normal, but then completely blow through the stroke and the pedal hits the floor and there is absolutely no brake. It just started happening suddenly while riding. No signs of a problem before. Ive bled the system through and through and replaced the fluid and have adjusted the brake play all to no avail. It feels to me like the master cylinder piston is broken or the o-rings inside are bad, and not causing a perfect seal every time the lever is depressed. but im not sure? what does this sound like to you guys, new master cylinder the fix, or maybe just a rebuild kit? Thanks for the help

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9/27/2017 2:37 PM

Is the rotor bent?

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9/27/2017 3:18 PM

CarlinoJoeVideo wrote:

Is the rotor bent?

no and neither is rim, there is no rubbing. that would be an obvious problem. this literally happens randomly and only like 5% of the time. so frustrating

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9/27/2017 3:43 PM

Do you notice more after you have been riding for a while? Or is truly just super random?

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9/27/2017 4:07 PM

you can get master rebuild kits for fairly cheap. I'd rebuild the master. like you said, sounds like a bad seal.

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9/27/2017 5:37 PM

It's the seals in the master cylinder. Rebuild it

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9/27/2017 5:47 PM

eilers434 wrote:

Do you notice more after you have been riding for a while? Or is truly just super random?

no super random. even occurs when the bike hasnt been ridden for hours so it cant just be the brakes getting ridden and hot or the fluid heating up. sounds like my suspicions of a blown seal and rebuild kit are what i need

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