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Thread: Master Cylinder rebuild 78 R100/7

  1. #1
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    Master Cylinder rebuild 78 R100/7

    Any advice or help on rebuilding the brake master cylinder on my 78 R100/7? I ordered the kit, should be here today, for the 14mm cylinder (I have a single brake rotor).

    Any videos/articles out there?

    What should i NOT do?

    Thanks in advance.

  2. #2
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    Jim: It is a straight forward job for anybody with a little mechanical experience around motorcycles (which i know you have!), which does not require much instruction. Don't spill any breakfluid on the frame or other painted parts.

  3. #3
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    I just finished this on a cylinder that had been sitting for several years. Someone has a very good tip about using dental floss to install the captive seal on the piston. I cannot remember where I read it but maybe someone else knows.

  4. #4
    Mike V. #30064 30064's Avatar
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    Mission Hills - San Diego, CA
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    Jimmy,

    Here's a picture link to my rebuild of the M/C recently. I would throw in an additional suggestion with the addition of an old caulk gun tip cut to length for the assembly of the rubber cup on the piston spool. Works a charm. Good luck with the rebuild.

    http://tinyurl.com/by4b8pj



    -Mike V. / San Diego
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    Mike V. / San Diego
    gruntyman66 MOA#30064
    78 R100/7 [orig. owner] / 81 R65 [restored]
    ABC-MOA-AMA / http://tinyurl.com/4df7hgs

  5. #5
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    WOW again!

    You guys are great!!

    I had forgotten that dental floss trick, and using the calking tube tip is really neat.

    I plan on doing this starting early Sat. morning.

    The advice about the brake fluid and paint is good.

    Mike, did I once hear you say to use DOT 4 and NOT DOT 5?

    Thanks again to all of you.

    I am amazed at how easy it is now to get great first-hand advice from first hand mechanics and also from some of you old geezers than it used to be when I was a member some 25 to 30 years ago.

    Its like having a wealth of knowledge right here at my fingertips.

  6. #6
    Mike V. #30064 30064's Avatar
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    May 2006
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    Mission Hills - San Diego, CA
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    Jimmy,

    Dot 3 or 4. Preferably Dot 4. Not the Dot 5 Silicone base. Be sure to change it annually. You know it's hygroscopic and absorbs ambient moisture which is cancerous for our brake's internal organs. Dot 4 has a higher boiling point - not that we need to concern ourselves so much about that for normal riding habits.

    Remember the key to M/C and Caliper rebuilds is; clean, clean. clean.

    -Mike V.
    Last edited by 30064; 04-26-2013 at 03:37 AM.
    Mike V. / San Diego
    gruntyman66 MOA#30064
    78 R100/7 [orig. owner] / 81 R65 [restored]
    ABC-MOA-AMA / http://tinyurl.com/4df7hgs

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