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Thread: 1988 K100 LT front brake reservoir

  1. #1
    Registered User naddy100's Avatar
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    1988 K100 LT front brake reservoir

    I'm getting some seepage around the front brake reservoir.

    There are a lot of parts in there, it seems by the fiche, and the parts vary quite a bit in price. There are $3 o-rings and $70 pistons. What's a reasonable strategy to sort out what's bad?

    Noel

  2. #2
    Still plays with trains. tinytrains's Avatar
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    If it is the original reservoir, it is time to replace the whole thing. My 88 K75 was doing the same thing a few months ago. There were small pits in the cylinder. I had a choice of spending $70 on a piston, and "hoping" it fixed it, or $200 for a cylinder/reservoir/piston assembly and know it was fixed. If I bought the piston and it did not fix it, then I had to spend $200 on top of the $70.

    I bit the bullet and bought the whole assembly. After 25 years who can complain.

    It was easy enough to change, but getting the air out the cylinder was tricky. Finally I stuck a syringe in the bottom of the reservoir and pulled up the plunger rapidly. That sucked the air right out.
    1988 K75 Low Seat
    2009 R1200R Roadster

  3. #3
    boomyrmyname,dangermygame boomyr's Avatar
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    I was able to replace just the piston on my '96 without replacing entire master cylinder. I'd check out the cylinder first. It may be the rubber on the piston just deterioted or hardened over the years.
    In my case I had brake fluid crystalized. I cleaned it up and polished it lightly with fine steel wool. I put the new piston in and have't had any problems.
    Check Beemer Boneyard for the parts, I've found them quite a bit cheaper and they are new OEM.
    Good Luck!

  4. #4
    Registered User tourunigo's Avatar
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    Quote Originally Posted by boomyr View Post
    I was able to replace just the piston on my '96 without replacing entire master cylinder. I'd check out the cylinder first. It may be the rubber on the piston just deterioted or hardened over the years.
    In my case I had brake fluid crystalized. I cleaned it up and polished it lightly with fine steel wool. I put the new piston in and have't had any problems.
    Check Beemer Boneyard for the parts, I've found them quite a bit cheaper and they are new OEM.
    Good Luck!
    yup, that's what you do. $42. I did it without having to bleed the line: force the front pads back and wedged (after loosening up the line at the master cylinder). Carefully continue to disassemble, clean and inspect for cylinder scoring and such. I'd be very careful though regarding steel wool ie a bit too aggressive on the rub or tiny particles. With a little fluid rubbed on for good luck put all back in reverse order. You can leave the whole thing on the bars but loose to rotate for easier work. Don't forget to fill the unit and get that wedge out of the pads. Put in a whole assembly if you like but that extra $150 in your pocket might be better spent elsewhere. Check out parts at: http://www.beemerboneyard.com/32722332037.html I did this last year and it's all been fine...... and I'm not really a mechanical wizard..... just a bit cheap. - Bob
    saltyfogriders@gmail.com
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    Larry's River, Nova Scotia, CANADA

  5. #5
    Registered User naddy100's Avatar
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    1988 K100 LT front brake reservoir

    Great! I see two mentions of the piston, and a little bit of difference in tactics. If those are the choices, I don't mind spending more for an (almost) assured fix, rather than possible repeated visits to the issue.

    Other thoughts?

    Lots of rain in my neck of the woods today!

    Noel

  6. #6
    Registered User naddy100's Avatar
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    1988 K100 LT front brake reservoir

    Okay, Bob was typing at the same time. Thanks for the ideas!

    Noel

  7. #7
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    I had seepage out from between the white plastic reservoir and the aluminum base. The $3 o-ring on the bottom of the white reservoir fixed it. If that's where the seepage is coming from, I'm not sure the piston would be implicated. Leakage from a piston (or piston-seal) defect would seem more likely to show up around the plunger.

    (1987 K75C)

    Edit: To clarify -- if there is seepage from between the reservoir and the base, the o-ring has to be implicated, because that's the only way fluid can get into that space.
    Last edited by JamesInCA; 02-11-2013 at 04:27 AM.

  8. #8
    Registered User naddy100's Avatar
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    1988 K100 LT front brake reservoir

    Seriously! This is good help for me. It sort of looks like a trip out to my parts bike to experiment with how these parts fit together.

    Noel

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