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Thread: Front Brake Master Cylinder

  1. #1
    Baby Twin
    Join Date
    Mar 2011
    Posts
    6

    Front Brake Master Cylinder

    I recently had a problem with my front brake feeling soft, eventually the lever could touch the bar.

    I have bled the front brake on two seperate occasions, but within a day of riding it feels soft again.

    Just a note, when bleeding via the master cylinder bleed valve I can never seem to get all the bubbles out. Its like there is an endless supply of tiny bubbles.

    I have checked for leaks but couldn't find any.

    Put simply do I need a new Master Cylinder?

    Cheers Guys

  2. #2
    One Liter Duc Eater apriliamoto's Avatar
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    Jan 2009
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    Co. Durham
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    772
    Hi mate, are these still on the standard lines? Just curious

    Also what is your bleeding method?

  3. #3
    Baby Twin
    Join Date
    Mar 2011
    Posts
    6
    I believe so, its an 02 plate. They are braided hoses with a clear plastic tube covering them. I'm not sure if this is standard for the model as I have no comparison.

    I am doing the following:

    Remove Reservoir Cap
    Connect tubing to master cylinder bleed valve other end in fluid in a jar
    *REPEAT*
    Press Brake Lever
    Release bleed valve
    tighten bleed valve
    *REPEAT*

    Then same proceedure for each caliper.

    Strange thing is the master bleed valve always has bubbles, they do not stop, almost like every time I pull the lever more air goes in. Might explain why after a day of riding (using the brake lever) they are soft again.

  4. #4
    One Liter Duc Eater apriliamoto's Avatar
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    Jan 2009
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    Co. Durham
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    772
    Ive always done the calipers first, right, left then the nipple on the lever. not that this really matters if its working ok for a day then goes spongy. I take it everthing is proper air tight?

  5. #5
    Baby Twin
    Join Date
    Aug 2011
    Posts
    1
    FWIW, I've had problems with the master cylinder on my '01 RSVR going 'long' or 'soft'.

    I replaced the original 5 or 6 years ago and the problems went away. Last week the problems
    came back and although bleeding got the brake back to what seemed normal, a few hours later
    it all went soft (back to the bars) again (and I ended up sliding along the tarmac at Cadwell Park!)

    There's definately something suspect about the OEM master cylinders once they're a few years old
    and I'm changing mine for a Brembo or AP radial before I ride her again.

  6. #6
    Evil Twin
    Join Date
    Feb 2011
    Posts
    294
    Mine goes a little soft at times (resist the urge!!) But it firms up ok when it's getting used ha ha. I've had bothedr in the past with front m/c and found that the tube from the resevoir to the m/c constantly trapped air. I just altered the bend/kink in it and it worked fine after that.
    Regards David

  7. #7
    Baby Twin
    Join Date
    Aug 2011
    Posts
    5
    O and just one more thing, Ruffle, I think I have a plaque for you
    enough said that cadwell park has some very slippery bits

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