GS1100E front master cylinder dripping from bottom air valve - fixable?

[oldGSfan]

Trying to fix my front brakes I got the Suzuki piston cup set plus a proper tool to insert the snap ring which really made it easy to assemble. I thought the problem was the snap ring not being in far enough into the cylinder (in the groove for the rubber boot), but apparently I didn't diagnose it well enough. Now I see that when bleeding the system I have a bubbling drip out of the bottom hole - is that a spring/check ball for a vent or something? Is it fixable, perhaps some crud got in there? I am thinking maybe I can poke a wire in there and blast with brake cleaner perhaps. Help!

[GSXR7ED]

I let my MC and components sit in this tank of cleaning solvent for a couple of days...cleared those tiny holes out!



Ed

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[oldGSfan]

OK took it apart and not a dirt issue. The hole goes through to the groove the circlip goes into, so it's past the seal. Makes sense, there is no way you can have a hole in a pressure chamber - duh. I realize I have the cup that goes in the little metal housing that slides over the aluminum piston shaft backwards, and that allowed pressure to seep past the seal. I read up on it on the forum as another person had the question and I misinterpreted it. And now I just simply analyze its operation and see how I screwed up. Oh well, mistake #6527234 and counting!

This is the old internals, took pic to show how it's assembled. I can't see how it would be any other way unless the middle black metal part that slides over the aluminum piston is backwards. But if it were the other way the cup would be too far in I think, possibly past the smaller fluid hole. I will bleed it tomorrow.

[oldGSfan]

Crap, still got fluid coming out of that hole, not even any pressure yet, just filled up reservoir and left it a while Getting frustrated, I've rebuilt probably a couple dozen MCs before and this one has me stumped for now.

[salty_monk]

Use an EX650 master cylinder unless you're worried about originality. I have one somewhere but I think it's remote reservoir type... They are easy to get anyway.

[oldGSfan]

Thanks, well I'd like to keep stock. The bore is clean and it should work. I will let it sit for a bit while I do other stuff, and come at it with fresh eyes a bit later.

[salty_monk]

Is it an OEM kit? The KL ones are known to have issues..

[oldGSfan]

Yes it's a brand new OEM kit, was sealed in a Suzuki package from Partzilla. Something basic is wrong, Assembly/direction of the middle piece and cup has me wondering. Somehow fluid is getting past that one I think, because it held pressure and the brakes worked fine, just leaked, so the primary would seem to be OK. There's an O-ring and a cup that fits inside the metal housing. It is weird and frustrating as I've had it on 3x now.

Is it an OEM kit? The KL ones are known to have issues..

[oldGSfan]

Thanks so much, got Email. The little cup tucks inside the metal slide piece. It can't go anywhere else, it's the same hole opening as the piston, and same outer diameter as the location it goes in on the slide piece. It makes sense that it should have the cup oriented the same way as the primary cup. So I'm a bit baffled but will ruminate on it while I work on some other bikes.

Tom, I sent you an email with a photo re the Master Cylinder. No luck attaching pic here.

I originally joined this forum in September 2006.....Owned my 83 GS 1100E from new.

Re kitted front master January 2016. Genuine Suzuki kit. your spring, cup, the really thin washer, then piston big end, then the metal slide piece with o ring is correctly positioned. The next part...the cup...... do not recall seeing that.

[oldGSfan]

Looks like I fixed it, no leaks and a solid lever. Last time I had the circlip in the right place but it was very tricky to get it pushed in far enough, I wonder if something was binding inside. Now time to ride.

[fbody_mike]

Are you talking about some fluid coming out of the hole at the bottom of the reservoir? I find that it is normal for some fluid to come out of the hole as the piston is depressed. The piston and its seal have to retreat past this point when you release the lever so that the master's bore can be refilled with fluid. When the piston then is depressed and travels past this hole, some fluid will be returned to the reservoir. Some masters even have a baffle plate over the hole to help control this flow. Now if you have air in the system, it will be dramatic as the air is trying to return to the reservoir as it will want to travel upwards.
Anyway, it sounds like you got it covered, some of these motorcycle brakes can be a pain to bleed too. One of my bikes I have to constantly tap the point where the brake lines split for the left and right caliper as air always loiters there.

[oldGSfan]

No not the internal hole, I know that one can shoot fluid up in the air so when I bleed, I go real slow (and use a vacuum pump), put cap on, etc - there is an external hole you can see from underside, close to the lever pivot. It may be a safety drain or something. I poked a wire through it and it passes through to the groove where the rubber boot fits, so it's well past any 'working' area. It would only be dripping from there due to something wrong internally and fluid getting past the second seal that is in the metal housing. I recall when assembling the time before (when it leaked) that things didn't seem right, it was really tough to push the piston down far enough to get the circlip in. Something hinkey was going on inside but when I took apart, nothing was munged. All is good in brake land now.

Are you talking about some fluid coming out of the hole at the bottom of the reservoir? I find that it is normal for some fluid to come out of the hole as the piston is depressed. The piston and its seal have to retreat past this point when you release the lever so that the master's bore can be refilled with fluid. When the piston then is depressed and travels past this hole, some fluid will be returned to the reservoir. Some masters even have a baffle plate over the hole to help control this flow. Now if you have air in the system, it will be dramatic as the air is trying to return to the reservoir as it will want to travel upwards.
Anyway, it sounds like you got it covered, some of these motorcycle brakes can be a pain to bleed too. One of my bikes I have to constantly tap the point where the brake lines split for the left and right caliper as air always loiters there.