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Old 08-09-2012, 07:32 AM   #1
CDN_bacon's Avatar
Join Date: Mar 2009
Location: West Houston
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Experience: 8 years

CRF 250X

Rear Master Cylinder Issues

see post over in Q&A section:

"Life is tough .... It's even tougher if you're stupid."
- John Wayne

"When I get sad, I stop being sad and be awesome instead. True Story" - Barney Stinson
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Old 08-10-2012, 10:39 PM   #2
Stunt Heavy
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Join Date: Jan 2012
Location: Houston
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Experience: 10+ years

'10 KTM 690 SMC
'03 Kawasaki 636
'01 Honda XR650R

Are you using the correct brake fluid? Some fluids will swell seals almost instantly. I saw a guy use cheapy no-name DOT 3 in a handbrake for a stuntbike one time and it almost immediately ruined the seals in the m/c.

What about crush washers, are they all good?

Another thing you could try would be to elevate the master cylinder far above the caliper, and bleed it that way. if you dont have a bike lift table you could always load it into your truck, then hang the caliper down past the tailgate.

Personally my method is this:

Fill m/c. pump vigorously with the cover off. 9 times of of 10 you can bleed off alot of air just through the m/c reservoir and pumping. Pump fast, then let it sit a few seconds....then pump slow. then fast again. (don't get excited...this is just bleeding brakes!)

Once I get some pedal/lever feel, I'll crack the bleeder, and put my finger over the bleed hole and pump away. this will stop relatively all air from getting back into the system, but fluid will seep out past your finger. Once this is pumping fluid well, I'll go back to traditional brake bleeding.

Oh, and by this time, i'm sure you've covered yourself and probably the pads and rotor and other goodies in brake fluid. Seal the system, and wash the bike down and your hands with water, nothing else. Brake fluid is extremely hygroscopic and will disperse from your brake pads/rotor/skin with just water. If you try and use the brakes and 'burn' the fluid out of the pads, you'll just ruin them.

Hope this helps. or if you're anywhere near missouri city I'd be glad to give you a hand if need be.
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