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Today's Topics Rear Master Cylinder

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    Today's Topics Rear Master Cylinder

    Continuing working on the GS. Dug through my moldy dust covered boxes and dragged out the rear master cylinder from the dead flies
    and mouse poop. I previously bought an overhaul kit so I'm good there. Took the snap ring and push rod off and.......nothing.
    Piston just sat there, corroded into place. I sprayed it down with lubricant and tapped the plunger. It moved down in the bore...
    and stayed there. Oofah. I tried air into the brake hose port and still no movement. Right now its out in the garage clamped in
    the vice soaking.
    The point of all this babbling is this I may be looking for a replacement master cylinder. Bike is a 1983 GS750E
    If anyone has one or ideas on how to save this one, I await with baited breath.

    Mad
    83 GS750E
    2006 ZX14
    2004 KTM 450 EXC
    2001 Yamaha Big Bear

    #2
    Assuming you figure out how to get the piston out be sure to use a flashlight down the bore and look for pitting in the aluminum. Brake fluid absorbs water and then the water causes corrosion. Of course, if people would change their brake fluid on the maintenance schedule this wouldn't be a problem but...
    Ed

    To measure is to know.

    Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

    Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

    Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

    KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

    Comment


      #3
      I'm thinking of taking my original front M/C off my 77 in to see how much it would cost for a machine shop to make a stainless steel sleeve for it. I'm sure it would cost a few dollars but I'd like to save it.
      I would keep soaking yours and again, heat is your friend. Perhaps a propane torch gently heating the housing will assist with removal of the piston.
      Last edited by Big Block; 08-22-2021, 11:14 PM.
      1986 1150EF
      2008 GS1250SEA

      Comment


        #4
        Had a brass sleeve installed in front m/c of my '80 original bore diameter and no further corrosion issues.
        1980 GS1000E

        Comment


          #5
          I installed a MC off a Ninja 300 on mine. There is a post here somewhere. It wasn't difficult but did need a hole drilled in the bracket, the GS hole centers are different to most other more modern stuff.

          Seems like one from a V-strom might also work. It works fine with the stock caliper.
          1980 GS1000G - Sold
          1978 GS1000E - Finished!
          1980 GS550E - Fixed & given to a friend
          1983 GS750ES Special - Sold
          2009 KLR 650 - Sold - gone to TX!
          1982 GS1100G - Rebuilt and finished. - Sold
          2009 TE610 - Dual Sporting around dreaming of Dakar.....

          www.parasiticsanalytics.com

          TWINPOT BRAKE UPGRADE LINKY: http://www.thegsresources.com/_forum...e-on-78-Skunk/

          Comment


            #6
            ATTENTION Big Block is the winner. I continued soaking it and applied heat with a small butane torch. Still nothing.
            So I got my roller stool over to the vice and while sipping a Modelo Negra and listening to my favorite light, family
            style rock, ( Marilyn Manson), sat and tapped the body with a small brass hammer. After about 5 minutes... THAR SHE
            BLOWS! Piston popped out. After cleaning everything the bore looked excellent so I rebuilt it. Another job done.
            Big Block, your brand new Waffle Iron is on its way as a prize.
            Thanks for all the help guys.

            Mad
            83 GS750E
            2006 ZX14
            2004 KTM 450 EXC
            2001 Yamaha Big Bear

            Comment


              #7
              I have the same master cylinder on my 83' GS750ES and I have an OEM rebuild kit from Suzuki.My rear master cyl bore is too corroded and I want to replace it.I looked-up the part and they only give the part# for the entire rear master cylinder assembly:there's no separate part # for the body alone.Do you know if another model(550ES,1150?)will use the same rear master cylinder body where I can swap(14mm)the part in with no fitment issues ? thanks,Bill

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