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Faulty master cylinder piston symptoms.

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    #1

    Faulty master cylinder piston symptoms.

    I've had an issue with my rear brake on the big bike and am not sure what to do next. It stops OK (I can skid if I want to) but I have to apply quite a lot of pressure in order to get much stopping power. Here's what I know:

    Pads...excellent and oil/grease free.
    Lines...great shape
    Fluid....clear, clean and free of air
    Pedal....solid feel, short throw (not spongy, at all)

    The brake is the same as the one on my 750. I've worked on it in the past and it operates perfectly. I'm guessing the problem may be the M/C piston....because I can't think of anything else. Any ideas??
    1980 GS1100E....Number 15!
    Tags: None
    #2
    What type of pads are you using?
    Is the rotor in spec?
    1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
    1985 GS1150ES stock with 85 Red E bodywork.

    Comment

      #3
      How old are the pads in years?
      If they are fairly new, were the pads bedded in correctly?
      If not it may have only about half of it's braking power being utilized.


      Life is too short to ride an L.

      Comment

        #4
        Maybe one of the rear pistons is stuck and all the braking force is coming from one side?
        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

          #5
          thanks

          Thanks for the suggestions, guys. The pads were on the bike when I got it but I've taken them out twice and they look very good. Both times, I lightly sanded them to make sure there was no grease or grime on them. The rotor is in spec and looks good.

          It did occur to me that the problem may be with a piston, as Ness suggested. Both seem to be wearing evenly so I don't know if that rules out anything or not.
          1980 GS1100E....Number 15!

          Comment

            #6
            Originally posted by chuckycheese View Post
            Thanks for the suggestions, guys. The pads were on the bike when I got it but I've taken them out twice and they look very good. Both times, I lightly sanded them to make sure there was no grease or grime on them. The rotor is in spec and looks good.

            It did occur to me that the problem may be with a piston, as Ness suggested. Both seem to be wearing evenly so I don't know if that rules out anything or not.
            Have you tried extending the pistons to full travel to make sure that they are ?

            Comment

              #7
              No

              Originally posted by Colin Green View Post
              Have you tried extending the pistons to full travel to make sure that they are ?
              No but I think I'll pull the pads again and take a better look at what's going on in there. I'm pretty sure the caliper could use a good cleaning and rebuild anyway so I'll probably do that first.
              1980 GS1100E....Number 15!

              Comment

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