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j_hurricane_y j_hurricane_y is offline
I'll have another
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Join Date: Sep 2006
Location: NoVA
Posts: 180
With all the wrenching I did tonight, I almost forgot to share a couple PM's I got from jweicht who as I mentioned earlier seemed to have similar symptoms to what I experienced. Here's his first reply to my request to share more details of his experience and what he did to fix it:

After a few more years and a lot of other similar threads to think about it, I'm convinced the root issue on my bike was only failure of the clutch throw-out bearing. As the bearing was going bad, I believe that it set up enough wobble/vibration in the bearing/slave cylinder/push rod/gearbox seal area that gearbox oil was allowed to seep past the gearbox seal and into the slave cylinder and past its seal, thereby contaminating the clutch fluid with gearbox oil. I don't believe that any DOT 4 fluid escaped from the clutch system, it was all gearbox oil into the DOT 4 fluid. It's probable that gearbox oil was mixed with my clutch fluid for a while but everything still functioned normally. I only knew there was an issue when the throw-out bearing totally failed and I effectively lost the ability to disengage the clutch (exactly like a clutch cable breaking). I believe that the slave cylinder was still functioning properly (for the most part), there was just essentially no bearing to push on the push rod anymore.

As part of the fix for my bike, I was convinced that the rear gearbox seal was shot so I replaced it as well as installing a new slave cylinder/throw-out bearing and flushing the system with fresh DOT 4 fluid. As was stated in the thread you started, I knew that if enough gearbox oil leaked from that seal it could work its way forward through the gear shaft hole (alongside the clutch push rod) and contaminate the clutch (didn't want that, already had to change the clutch on my '94 R1100RS due to a bad "early model" design by BMW). To change the gearbox seal I had to pull the gearbox for adequate access, that's a real joy if you haven't done one yet.

In hindsight and if I had to do it all over again, I would not have changed the gearbox seal at that time. After changing the slave cylinder and flushing the system with DOT 4, I would have just run the bike and pulled the slave cylinder in 500 or 1,000 mile increments for a while to see if the seal was still leaking. In the end, I still think the only reason the seal leaked was due to the bad throw-out bearing and once that was no longer an issue the shaft may have run perfectly concentric again. If indeed the seal was bad and I saw gearbox oil after pulling the new slave cylinder, only then would I have pulled the gearbox and changed the seal.

On your bike, the amount of "liquid rust" present makes me think there was somehow an excess amount of moisture in the area of your slave cylinder. I didn't see anything in your thread about the actual condition of your throw-out bearing, or if had actually totally failed like mine.
I replied with "Thanks so much for your throrough reply! I am debating the gear box pull for the seal install. If I drain the gear box and see no evidence of DOT4 in it, can I safely conclude the mixing of the clutch fluid and gear oil was only one way? ... or is it possible the clutch fluid can travel all the way through the gear box w/o contaminating it, but still contaminate the clutch? I obviously don't have a handle on how it's all configured in there and the service manual doesn't make it clear to me. Re my throw out bearing, again I'm not sure how it's supposed to look. Mine didn't come apart as your did; no ball bearings. However it does flex/pivot; should it be rigid?"

His response:
Glad if I was able to help at all. Again I have to say that all of my response was based upon my experience and opinion, as I recognize that there are those who certainly have more experience than me in these areas.

Having said that, I'd say that yes, if you cannot discern any brake fluid in your gearbox oil then the liquid transfer was only one way (just like my experience, only gearbox oil into the clutch system).

On your second question, the answer is again yes, because there really is no direct connection between the two possibilities. By that I mean the gearbox input shaft is hollow and this is where the clutch pushrod resides and where it moves back and forth to disengage the clutch. The outside of the shaft rides in two seals (and bearings, of course), one at the front of the gearbox (just aft of the splined end of the shaft which engages the clutch splines) and one seal at the rear (just forward of the forward end of the clutch slave cylinder/throw-out bearing when installed on the gearbox). If DOT 4 fluid were to leak/escape from the slave cylinder it has two possible places to go: forward past the shaft seal into the gearbox and/or forward through the inside of the hollow shaft toward the clutch. So, even though fluid could go "through the gearbox to the clutch", it would only do so via a hollow shaft (the gearbox input shaft) and be totally isolated from the gearbox internals.

On my S, even with all of the gearbox oil/gunk I found when I pulled the slave cylinder the inside of the hollow shaft was dry (as it's supposed to be). There have definitely been cases where the rear gearbox seal leaked and the oil made its way forward through the shaft and contaminated the clutch, maybe I just caught mine before that happened or instead of going that route it went instead past the slave cylinder and into the clutch fluid because the bad throw-out bearing's gyrations made that the path of least resistance. That is my opinion of what happened to my bike: it all comes back to that bad throw-out bearing being the source of all the problems. Can't say that I ever read/heard of DOT 4 fluid leaking forward to the clutch but that's not to say that it hasn't happened.

As for your throw-out bearing, if there is much "play" at all on the end that engages with the pushrod, the bearing is going bad in my opinion. It is not a demountable ball bearing (not meant to be disassembled), therefore it should freely rotate but not really have play (or flex/pivot) to speak of. If you've already gotten your new slave cylinder you'll be able to compare a new/good bearing with your old one. Per my thread on the forum, I recommend that you liberally grease the balls of that bearing before installing it. My bearing was dry when I took it apart, I'd bet money that's why it failed in the first place and started my bike's chain reaction.

I don't mind you using in the forum any of the info (or my opinions) I've provided, and I'll be glad to help in any way I can.
Gotta love the kind souls out there willing to help a noob like me.

Note that despite what I believe to be good advice from jweicht regarding simply changing the slave cylinder and monitoring periodically, I decided that I had the bike far enough apart already that I might as well do a spline check and lube if necessary per repoe3's Dr. Splinelube thread.
"I love twins!"
Old 10-03-2008, 07:26 PM
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