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Leaking rear brake MC?

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  • #1

    Leaking rear brake MC?

    Hello,

    I am the happy (relatively new) owner of an 1979 XS 1100, a transplant from another forum member in SoCal:



    I love the bike and enjoy taking it to the hills here in Colorado, runs great even on dirt roads.

    Time to introduce myself and start asking questions...

    I noticed that the lower part of the rear brake master cylinder looks wet.




    Do I have to rebuild it?

    Thanks in advance for any advice and greetings from the Front Range,
    Armin
    Last edited by QTreiber; 10-05-2010, 09:15 PM.
    2018 Suzuki DR650, no XS1100 right now.
    Tags: None
  • #2
    Probably wouldn't be a bad idea rebuilding the rear MC....

    http://store03.prostores.com/servlet...-XS1100/Detail
    2H7 (79) owned since '89
    3H3 owned since '06

    "If it ain't broke, modify it"

    ☮

    Comment

    • #3
      Could wait till winter probably. Then you could pull it apart and see what it looks like and then decide is you need the kit or not.

      Have fun bleeding that SOB.
      Nathan
      KD9ARL

      μολὼν λαβέ

      1978 XS1100E
      K&N Filter
      #45 pilot Jet, #137.5 Main Jet
      OEM Exhaust
      ATK Fork Brace
      LED Dash lights
      Ammeter, Oil Pressure, Oil Temp, and Volt Meters
      Green Monster Coils
      SS Brake Lines
      Vision 550 Auto Tensioner

      In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

      Theodore Roosevelt

      Comment

      • #4
        If it were my bike, next wet weekend, I'd pull it off, open it up and clean the inside and components really well. Reassemble and have the pleasure of bleeding it out. Then see if the problem persist. If it does, then order the rebuild parts.

        Nothing wrong with rebuilding the first time if you rather get it fixed once and be done. More I think of it and the PITA it is to bleed that rear mc, I'd probably go that route. But, cleaning them up will do the trick most of the time.
        Life is what happens while your planning everything else!

        When your work speaks for itself, don't interrupt.

        81 XS1100 Special - Humpty Dumpty
        80 XS1100 Special - Project Resurrection


        Previously owned
        93 GSX600F
        80 XS1100 Special - Ruby
        81 XS1100 Special
        81 CB750 C
        80 CB750 C
        78 XS750

        Comment

        • #5
          +1 on the above...

          Even with limited knowledge, pulling the rear m/c and components off, cleaning them, and reinstalling is about a 3 beer project...maybe 4 beers

          never take 2nd chances with brakes!!! There arent too many things in life as scary as tooling around on a bike at 30 or 40 + mph, hit the brakes and no friction!!!
          '81H (my first XS ) "Grey Ghost"
          Stock Pilots/ 110 mains (to change)
          4:1 Jardine w/ headerwrap
          Windjammer(wiring issues)
          SonyMarine unit for Ipod/Polk Speakers
          New paint/brakes to come!!
          ===============
          '80G FrankenBike (parts bike)
          ===============
          '80G to fix "BlackSunshine"
          Stock Pilots/125 mains
          Pod filters; 4:1 Kerker??
          SS Brake lines w/ new M/C's
          LED Brake Lite
          Needs paint....

          It is better to be thought a fool than to open ones mouth and remove all doubt....

          Comment

          • #6
            Thanks for all the great advice! I ordered the rebuild kit. This is a first to me so I will research some posts here on rebuilding and bleeding, which seems to be a bit of a challenge.

            Can someone please explain how cleaning the MC could actually fix the problem? How does debris lead to leaking? By clogging pathways?

            Looking forward to get this done!

            Greetings from Colorado,
            Armin
            2018 Suzuki DR650, no XS1100 right now.

            Comment

            • #7
              If a piece of dirt or debris got stuck under a seal when the piston slid in or out it could cause a leak.

              The biggest issue with bleeding is the crazy way the MC sits below the caliper. So gravity tends to work against you and cause air bubbles. Very hard to pull fluid. I have resorted to the Mity Vac for it.
              Life is what happens while your planning everything else!

              When your work speaks for itself, don't interrupt.

              81 XS1100 Special - Humpty Dumpty
              80 XS1100 Special - Project Resurrection


              Previously owned
              93 GSX600F
              80 XS1100 Special - Ruby
              81 XS1100 Special
              81 CB750 C
              80 CB750 C
              78 XS750

              Comment

              • #8
                This is an extreme example but kind of shows you how far that debris can go. Like DGXSER says it can cause leaks. I have not had any problem so far as bleeding my rear M/C's but the fronts have caused me no end of grief.
                2-79 XS1100 SF
                2-78 XS1100 E Best bike Ever
                80 XS 1100 SG Big bore kit but not fully running yet.
                Couple of more parts bikes of which 2 more will live!

                Comment

                • #9
                  Holy crap rasputin! Did you actually get that clean or did you replace that?
                  Nathan
                  KD9ARL

                  μολὼν λαβέ

                  1978 XS1100E
                  K&N Filter
                  #45 pilot Jet, #137.5 Main Jet
                  OEM Exhaust
                  ATK Fork Brace
                  LED Dash lights
                  Ammeter, Oil Pressure, Oil Temp, and Volt Meters
                  Green Monster Coils
                  SS Brake Lines
                  Vision 550 Auto Tensioner

                  In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

                  Theodore Roosevelt

                  Comment

                  • #10
                    Gnarly

                    Without doubt, that is the rattiest looking master cylinder that I have seen! I'm just wondering how many years that it took the brake fluid to congeal like that!
                    1979 F
                    Mac 4-2 Exhaust
                    T-Kat Fork Brace
                    Spade Fuse Box Mod
                    Stainless Steel Braided Brake Lines
                    140.0 Main Jets
                    45.0 Pilot Jets
                    266 X-2 Needle Jets

                    Comment

                    • #11
                      I got it cleaned out and it works fine. I do have a rebuild kit that will be going in to be on the safe side though. It does not take all that long to congeal like that either as this particular one seems to have had a mix of DOT3 and DOT5 fluids in it. Stirred in a bit of DOT3 and it went back to fluid form. Left it a few weeks and it was back to the same as in the pic. Do Not Mix different types of brake fluids like this PO did .
                      2-79 XS1100 SF
                      2-78 XS1100 E Best bike Ever
                      80 XS 1100 SG Big bore kit but not fully running yet.
                      Couple of more parts bikes of which 2 more will live!

                      Comment

                      • #12
                        Success!

                        Well, I took - with the help of a very capable local forum member - the rear MC apart.

                        Things did not look quite as bad as the pictures above, but there was some debris and corrosion:





                        Cleaned everything, installed new piston, bled the system. The inner surface of the cylinder is not perfect, but pretty smooth after gentle polishing.

                        So far no leaks and the break seems to grab stronger - success!

                        Thanks again for all your help,
                        Armin
                        2018 Suzuki DR650, no XS1100 right now.

                        Comment

                        • #13
                          Congrats on a job well done! Now go brake something!!
                          Life is what happens while your planning everything else!

                          When your work speaks for itself, don't interrupt.

                          81 XS1100 Special - Humpty Dumpty
                          80 XS1100 Special - Project Resurrection


                          Previously owned
                          93 GSX600F
                          80 XS1100 Special - Ruby
                          81 XS1100 Special
                          81 CB750 C
                          80 CB750 C
                          78 XS750

                          Comment

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