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Thread: Brake Master cyl leak 85 R80

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  1. #1
    Registered User
    Join Date
    May 2006
    Posts
    162

    Brake Master cyl leak 85 R80

    The master cylinder has been on there for nearly 30 years. I changed the fluid several weeks earlier before I noticed the drip. I washed it to make sure and the leak returned so it wasn't spilled fluid. It seems to be leaking at the joint btwn the master cylinder and the hand grip assembly. I have a new replacement MC unit but I don't want to waste it. Is there a gasket in the joint? I used BMW DOT 4 fluid. The brake works fine. After a week sitting there was a table spoon worth of fluid leaked (painted parts are all protected w/ plastic sheet). Any suggestions what to do now?

  2. #2
    Registered User
    Join Date
    Dec 2007
    Location
    Reno, NV
    Posts
    1,962
    You can buy just the plunger that goes in the master cylinder, and replace that. Don't forget the o-ring that goes where the reservoir connects - idiotically that doesn't come with the rebuild "kit"

  3. #3
    Airhead or Nothing
    Join Date
    Feb 2008
    Location
    Shoreline, WA
    Posts
    41
    I had the same issue with my '81 R80G/S and bought the new (and expensive) plunder... cleaned the M/S installed the plunger and still had the leak... bought a M/S hone and very, very lightly honed the M/S and installed the new plunger again and still had the leak.

    In the end I bought a new complete M/S from Motobins for not too much more than the plunger!
    "Punk rocks what its all about" J. Strummer

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