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Discussion Starter · #1 ·
OK. Here's a new one on me. When I go from sea level to 7 or 8 thousand feet over the Sierra Nevadas to Lake Tahoe at 6,000 ft my clutch will not completely disengage when I pull the lever all the way in. Shifting becomes notchy and abrupt and sitting at a stand still in first with the clutch pulled in the bike still wants to go, I have to hold it back with my feet. When I come back to sea level, it's fine. Any ideas ? And yes I had the dealer change and bleed my clutch fluid last time it happened last year but this year its doing it again.
 

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That's definitely not normal, I frequently go from home which is 7ft above sea level to Palomar mountain which is 6100 ft above sea level, no change in clutch engagement.
I'm thinking you have some air in the system. Bleed the slave cylinder and the master cylinder, I typically find bleeding the master cylinder has the most effect on the lever, at least for my bike.

The way I bleed my master cylinder is adjust the lever to it's outermost position, pull the lever all the way in and slowly crack the bleeder with a towel around the bleeder nipple the retighten, then release the lever (I don't have a hose small enough to fit over the nipple) but it works. Then I clean the area with simple green and top off fluid as necessary.
I do this once a year or as needed.

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Definitely sounds like air in the clutch fluid. Looks like it will need to be an annual maintenance item. If it solved it last time, it should solve it again this time. You could also try reducing the amount of fluid in the reservoir.
 

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one trick is to zip tie your lever as tight as possible and leave over night, it helps compress air out of system. make sure the reservoir is at the high point and that the hose is not looping above the reservoir.
 

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Air inside teh clutch system expands at the higher altitude, so the air bubble in your clutch system effectively gets bigger the higher you go. You have to compress this bubble back down before your clutch starts working. hence at higher altitude you have less clutch lever available.
 

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Discussion Starter · #8 ·
KTM went to dot4 fluid systems I hear on later Superdukes. Looking into changing over. Anybody here also using Magura mineral oil based system like me ?
 

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My '15 uses mineral oil. To change over you'd have to change some hardware or at least seals I think, the DOT4 would not be compatible.

I bleed mine at the master cylinder to improve feel a few times a season. It seems like its been drawing in air somewhere since I bought it with less than 400 miles. It's never gotten any worse so I haven't started replacing stuff yet.
 

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Discussion Starter · #10 ·
My '15 uses mineral oil. To change over you'd have to change some hardware or at least seals I think, the DOT4 would not be compatible.

I bleed mine at the master cylinder to improve feel a few times a season. It seems like its been drawing in air somewhere since I bought it with less than 400 miles. It's never gotten any worse so I haven't started replacing stuff yet.
OK. Glad to hear it hasnt gotten to the point of stranding anybody on the road or stuff like that.
 

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Woody was up over 12K feet recently (and has been to 14K) and is now back here at 650 feet above sea level. Never a change in clutch performance. I would imagine air in the system could react differently at altitude.
 

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You know what's funny... when I saw this thread a week ago I thought 'Nope, never happened to me.'

But, a couple days ago I trailered the bike up to Lake Alpine and rode around the Sierras for a couple days. Lo and behold, I get the bike out at 7500 feet---and the clutch has miles of free play and the engagement point is just at the bar. It wouldn't go into neutral while running, since there was still a little drag even with the clutch all the way in.

I've had it up there in the past and it never did that. I did notice now, however, the clutch fluid was above the max line. It must be getting air or moisture in the system somehow..?
 

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Air is compressible.
Air is also decompressible. (Expands as pressure is released, like when you go higher?)

So the volume of the air-bubble in your clutch system INCREASES as the pressure drops. (Bubble gets bigger due to lower air pressure outside)

Because air is compressible you need more lever travel to compress that bubble down before you get hydraulic pressure back.

Big bubble = more free play, small bubble = less free play…

Same bubble = small at sea level and big at the top of a mountain!
 
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