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Master Cylinder Replacement Options

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    #1

    Master Cylinder Replacement Options

    After multiple rebleeds, new lines, and rebuilding the MC with new oem piston etc, I'm close to tossing this thing. Bled it today and within a few hours it was soft and needing to be pumped up to have a responsive feel. The only things I can think of are that I need to replace the copper orings (thanks Chef) or that I just need to get a new mastercylinder. Who's wise as to what NEW master cylinders I can buy (not taking any chances with used MCs). I'm trying to remain cost effective, so no 400 dollar fancy deals

    Thanks!
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    #2
    Originally posted by J_C View Post
    After multiple rebleeds, new lines, and rebuilding the MC with new oem piston etc, I'm close to tossing this thing. Bled it today and within a few hours it was soft and needing to be pumped up to have a responsive feel. The only things I can think of are that I need to replace the copper orings (thanks Chef) or that I just need to get a new mastercylinder. Who's wise as to what NEW master cylinders I can buy (not taking any chances with used MCs). I'm trying to remain cost effective, so no 400 dollar fancy deals

    Thanks!
    Not sure for what bike it is, but if you have twin disks the inside bore diameter of the M/C should be 5/8" (16.83mm) and for a single disk usually 1/2" (13mm) for the front ones. If the bore is till smooth inside and not pitted or marked then a full M/C kit should include all the internals, rubbers spring and piston and you should have no problems.
    If the M/C is in good condition and you are losing pressure then you have to make sure that it is not caused by something else, such as the calipers or pipes. Are you bleeding it correctly and getting all the air out? Have you used new clean brake fluid etc. Check for any leaks even how slight.

    If it is definitely the M/C just have a look on ebay as there was a universal (new) type for sale for about $79. the kits are also on sale there showing pictures of the parts.

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      #3
      Try a late model GSXR master with the remote resorvoir. I use them & absolutely LOVE them. They work great & they look AWESOME! It doesn't matter which one you use as I've tried them all & had no problems with any. Ray.

      Comment

        #4
        Hey there,
        I'm currenlty hassling with my own M/C issues, and I bought one of those ebay M/C's. It's a very, very nice unit, but won't work with clip-ons and my "S" fairing. It's brand-new and never had fluid in it. I'll let it go for $50.00 incl. shipping, if you're interested.
        Hugh
        QUOTE=Matchless;780557]Not sure for what bike it is, but if you have twin disks the inside bore diameter of the M/C should be 5/8" (16.83mm) and for a single disk usually 1/2" (13mm) for the front ones. If the bore is till smooth inside and not pitted or marked then a full M/C kit should include all the internals, rubbers spring and piston and you should have no problems.
        If the M/C is in good condition and you are losing pressure then you have to make sure that it is not caused by something else, such as the calipers or pipes. Are you bleeding it correctly and getting all the air out? Have you used new clean brake fluid etc. Check for any leaks even how slight.

        If it is definitely the M/C just have a look on ebay as there was a universal (new) type for sale for about $79. the kits are also on sale there showing pictures of the parts.[/QUOTE]

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          #5
          How would a remote resevoir work? I'm interested, but I'm trying to keep it as simple as possible; that may not fit the look of my bike.

          I was definitely considering the ebay model you guys are referencing. Do we know anyone who has first hand experience with it?

          I completely rebuilt the MC with the rubber & spring & piston etc. I might take the resevoir off and try lightly sanding around the lid, as I did notice (well Kris V noticed) a very little bit of fluid where the resevoir meets the MC. Perhaps thats enough to cause the softening.

          Comment

            #6
            Originally posted by J_C View Post
            How would a remote resevoir work? I'm interested, but I'm trying to keep it as simple as possible; that may not fit the look of my bike.

            I was definitely considering the ebay model you guys are referencing. Do we know anyone who has first hand experience with it?

            I completely rebuilt the MC with the rubber & spring & piston etc. I might take the resevoir off and try lightly sanding around the lid, as I did notice (well Kris V noticed) a very little bit of fluid where the resevoir meets the MC. Perhaps thats enough to cause the softening.
            If you have the square white plastic reservoir, it seals with an o-ring to the aluminium base. The plastic also becomes damaged by UV light and becomes brittle with age. The o-ringcan be bought at an bearing and seal supply shop. The reservoirs are still available, but quite expensive. Both holes into the bore must be open, the small one easily gets clogged.
            I usually clamp a pipe or old handlebar in a vice and mount the M/C on it, then attach an old brake pipe loop it up higher than the M/C and even extend it with another transparent pipe into a bottle of brake fluid. Fill the reservoir and pump the handle until no air is pushed into the pipe. If it starts pumping properly and there are no leaks then you should be good.

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              #7
              I actually have the round one. Its a new resevoir with a new rubber oring, but I can certainly give it a shot, thanks for the feedback

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                #8
                Besides the copper washers did you rebuild the calipers?
                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

                  #9
                  Yes I did, I pulled the pistons out, washed them, and used a rebuild kit.

                  bwringer made an interesting point to me, which is that the washers, if not good, would allow fluid to squirt out under pressure. I'm going to focus on the MC for now.... first trying to stem a leak that may exist between the resevoir and MC, then going new MC. Then I'll get into washers and possible piston trouble (though there are no leaks around the calipers that I can see)

                  Comment

                    #10
                    Pulled off the resevoir yesterday and looked for anything that could be breaking the seal but didn't see anything. I lightly sanded all the contact spots and screwed it back in. If I had to take a guess, it's probably the bore of the MC. I heard a very very quiet squishy noise as I was working the lever, and if I repeatedly squeeze it like a quarter of the way some very very tiny air bubbles come up.

                    I'm going to see how the pressure holds up over the next few days, and then I may be on touch you hp to go for that replacement MC off ebay.

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