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Clutch slave failures because of constant holding in clutch lever?


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Kate has now burned through 3 clutch slaves,(I think one might have been faulty or I screwed it up when installing as it failed at less then 2500 miles). For sure she has had one fail on her K1200RS with 20,000 miles and her original one in the GSA at about 50,000 miles in the middle of Alaska, so this was on two different bikes. I was thinking this cannot be a coincidence as I have not heard of to many of these failing although one failed at the UN. I realized that she never uses neutral. She can sit at a light for 3 minutes and will hold in the clutch. The only time that bike goes into neutral is when I park it for the night. So I am wondering is holding the slave against a rotating pushrod, pushing on the rotating clutch spinning the slave more then it should be? I am the exact opposite, if I sit more then 5 seconds it goes into neutral and I have no problems as of now. Anyone have any ideas, or have you burned one out and what is your style of clutching?

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Joe Frickin' Friday

Ken, what is the exact nature of the failure?


The slave unit on the hexheads is a hydraulic piston with a thrust bearing on one end of it. The thrust bearing (just a ball-bearing or needle/roller-bearing unit) is what deals with the rotation of the pushrod. All clutches (hydraulically-actuated or not) have this thrust bearing. It's spinning any time the engine is spinning, but it's only under high load when you actually hold the clutch in. With a lot of clutch-in time, it can wear out, but we're talking about 100K miles. Keith (oOPEZOo)had one go to pieces on him a few miles short of BRR this spring; his bike had that kind of mileage. Symptoms would be a grinding/growling feeling as the bearing and races progressively roughen up and wear away, until you get to a point where they're so worn and wrecked that you can't even get the clutch to fully disengage. 135K miles on my old RT, never had a throwout bearing failure.


The other kind of failure would be a loss of hydraulic sealing in the slave cylinder/piston assembly. More and more leakage/loss of clutch fluid, until the handlebar reservoir empties completely and you get to the point where you can't fully disengage the clutch. The seal(s) on this piston experience wear whenever they move, so time spent with the clutch lever held to the handgrip shouldn't affect this; I would expect wear/failure here to correlate with shifting activity: many shifts = many movements of the slave piston.


So...was it a throwout bearing failure, or a loss of hydraulic sealing on the slave cylinder?

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Both were different, on the GSA, no fluid loss but the slave fell apart once off the bike so I assume a throwout bearing failure. The KRS slave lost fluid. The second slave that prematurely wore out on the GSA simply got worse with miles and would not fully disengage the clutch, but looked fine when pulled off the bike. So I wonder if the high load with the clutch being held in all the time contributed to the failures, or incredible coincidence?

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