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Thread: Rear Brake/Master Cylinder

  1. #1
    Registered User
    Join Date
    Mar 2006
    Location
    Raleigh NC
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    401

    Rear Brake/Master Cylinder

    Before you ask, I did check the older threads that addressed this problem and was able to address a couple of questions with those such as seating the plunger wiper/washer with a long socket and probing the fluid hole in the MC with a bent wire. This is a 1984 R100RS that sat outside under a tarp for 8 years in the PO's backyard here in humid NC. I replaced the plunger assembly after polishing the MC. The caliper is rebuilt with new parts and the flexible line is new Spiegler SS line. I applied vacuum to check the line from the MC to the caliper bleed screw and also from the MC outlet to the resevoir. I had an "ah-ha" moment when I realized the pedal was not correctly adjusted and was pushing the plunger in slightly and blocking the flow. When I was satisfied that the system was clear from the reservoir to the caliper, I hooked it up and started to pull fluid through with a Mighty Mac. It took a little and then stopped. The fluid level isn't going down. I've gone through this routine three times, removing, checking and replacing the assembly with the same results. The lines appear clean and the MC appears to work correctly. The caliper is suspended and positioned to put the bleed screw at the high point. I appreciate your thoughts on this before I go shopping for a new MC.
    Sent from a Galaxy, far, far away

  2. #2
    TGHSMITH
    Guest
    I would try to get fluid through the system without using the vac. open the bleeder and use slow smooth pumps on the brake foot lever(allow time to refill at the top off the stroke), maybe try cracking open the tube nut on the back of the m/c to see it fluid is pumping there. shoot me a pm if still no luck, won't be riding around here this weekend anyways.

  3. #3
    Registered User
    Join Date
    Mar 2006
    Location
    Raleigh NC
    Posts
    401
    Thanks, Todd. I disconnected the line at the MC and was pleased by the mess I made. I ran a tube from the bleeder into a bottle and began the slow pump/loosen/tighten... The result is a firm pedal. Thanks for your suggestion. The Mighty Mac may well have induced a problem. This is two I owe you for. My RT was the one you helped to replace the final drive seal on at the ABC tent at the Johnson City MOA National. Enjoy the snow. I know I won't.
    Sent from a Galaxy, far, far away

  4. #4
    TGHSMITH
    Guest
    no problem, I have a mighty-vac hung up on a nail in my garage, it has a very thick layer of sawdust and crud on it, hasn't been moved in years...

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