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Thread: Front Brake Master Cylinder Leaking, 89 K75C

  1. #1
    DEANCOX
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    Front Brake Master Cylinder Leaking, 89 K75C

    Fluid is dripping out of the master cylinder assembly. In conversation with the parts desk at a SoCal BMW dealership, it was their opinion that it was like to be the master cylinder that was leaking and not the o-ring below the resevoir.

    I have front dual discs, rear drum, no ABS.

    Have any of you experienced this? Can the master cylinder be "tuned up?" I don't like the north of $200 price tag on a new master cylinder.

    I have the manual that describes and shows the disassembly and reasssembly of the master cylinder, but it doesn't talk about whether you can stop a leak or any tune up type procedure.

    Thanks in advance!

  2. #2
    Mars needs women! 35634's Avatar
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    You probably just need a rebuild. Hopefully the bore isn't damaged. I used one of these and it's lasted longer than the original...$45 http://www.beemerboneyard.com/32722302356.html
    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

  3. #3
    Mars needs women! 35634's Avatar
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    PS_if you order online from Beemerboneyard enter BMWMOA under "source code" in the "other information" box on the shipping and billing page for a 10% discount.
    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

  4. #4
    DEANCOX
    Guest
    Quote Originally Posted by 35634 View Post
    You probably just need a rebuild. Hopefully the bore isn't damaged. I used one of these and it's lasted longer than the original...$45 http://www.beemerboneyard.com/32722302356.html
    Thanks! Perfect.

  5. #5
    Registered User
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    I bought a brand new master cylinder in January and I continue to get weeping of hydraulic fluid around the hollow bolt (banjo joint) crush washers. So purchasing another master cylinder is not always the solution to a problem.

    What kind of washers of you using: copper or aluminium?

    You may want to consider a new hollow bolt and/or new washers.
    1993 K75S Mystic Red Pearl
    2007 K1200GT 997 Blue

  6. #6
    Still plays with trains. tinytrains's Avatar
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    My master cylinder was leaking and it turned out the banjo nut on the brake line needed tightened. Check that first. I am amazed my 23 year old seals are still good!

    Scott
    1988 K75 Low Seat
    2009 R1200R Roadster

  7. #7
    DEANCOX
    Guest
    Quote Originally Posted by TinyTrains View Post
    My master cylinder was leaking and it turned out the banjo nut on the brake line needed tightened. Check that first. I am amazed my 23 year old seals are still good!

    Scott
    It isn't the banjo bolt or crush washers, it is leaking out of the handle area. A new master cylinder rebuild kit arrives today. I will let you all know how it goes.

  8. #8
    DEANCOX
    Guest
    Got the rebuild kit from Beemer Boneyard, easy peasy replacement. Bled the brakes with my Mighty-Vac speed bleed and jumped on the bike and made a run to San Francisco yesterday from LA. Nice to have front brakes!

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