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just a quick question? does anyone know the seal number and manufacturer for the clutch cyl.seal? I am not looking for the oem number since I don't trust their quality.
 

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Fred said:
just a quick question? does anyone know the seal number and manufacturer for the clutch cyl.seal? I am not looking for the oem number since I don't trust their quality.
Even if it is an available part from somewhere, I still would not re-build the slave cylinder. I know one of mine, and likely many others failed not because of the seal, but because of the little ball thrust bearing in the end of the piston. That is the "throwout" bearing for the clutch, and is spinning all the time the engine is running. A lot of motion on a very small bearing, lubricated only with the little bit of grease in it from the factory. Rebuilding a slave with a new piston seal will only make bearing failure very likely to be next. When that bearing tightens or seizes, the piston spins in the cylinder, wiping it out immediately.

The clutch master cylinder is rebuildable, with parts available from the dealer, but in over 6 years on this site have never heard of one going bad.
 

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Fred,

I think David is probably correct about rebuilding the slave cylinder. There have also been pictures posted recently of a new slave cylinder design. Apparently BMW has decided there might be a problem and modified the part slightly. I think I'd look for the new design slave cylinder instead of rebuilding one of the old designs.

Good Luck,
Kevin
 

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dshealey said:
That is the "throwout" bearing for the clutch, and is spinning all the time the engine is running. A lot of motion on a very small bearing, lubricated only with the little bit of grease in it from the factory.
David.....OMG.... that bearing at the end of the piston spins at "all times"? I thought it spun only when the clutch was depressed under pressure.
 

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David knows that, HoodooDrum it was a slip of the typing fingers.
 

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Actually...

hoodoodrum said:
David.....OMG.... that bearing at the end of the piston spins at "all times"? I thought it spun only when the clutch was depressed under pressure.

...and David can speak for himself, but I would be willing to bet that the bearing spins MOST of the time, if not all. It would seem that even the lightest contact would spin the bearing...hence, it wears out, ruining the cylinder. Hum Dave????
 

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hoodoodrum said:
David.....OMG.... that bearing at the end of the piston spins at "all times"? I thought it spun only when the clutch was depressed under pressure.
Yes, it spins all the time. The spring in the slave cylinder keeps pressure on the piston, forcing it and the clutch actuation rod forward against the diaphragm clutch spring. The pressure is not near as much as when you pull the clutch handle in to push the clutch spring open, as the pressure is then pretty high, but the actuation rod is always under spring tension from the cylinder spring. When you install the slave cylinder the pressure you have to push it in with, and use the screws to pull it in and seated, is always there, so the bearing is always spinning when the engine is running. Can't avoid it.
 

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Tourdog said:
David knows that, HoodooDrum it was a slip of the typing fingers.
No typing slip, the actuating rod and piston bearing spin all the time the engine is running. Even when the clutch is pulled in, and or transmission in neutral, the rod is still pushed against the diapraghm spring, which is spinning with the engine. The only thing in the whole clutch assembly that ever stops spinning is the clutch disk itself when the clutch is disengaged. The rest of the assembly: drive plate, diapraghm spring, pressure plate, and clutch cover plate are all attached to the engine output shaft, so do not stop spinning.
 

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cccpastorjack said:
...and David can speak for himself, but I would be willing to bet that the bearing spins MOST of the time, if not all. It would seem that even the lightest contact would spin the bearing...hence, it wears out, ruining the cylinder. Hum Dave????
Right. You have replaced slave cylinders, and know how much spring pressure is on it when you install it. With the clutch released, the slave cylinder spring is pushing pretty hard on the piston. That pressure never goes away. The bearing sees considerably higher pressure when the clutch diapraghm is being pushed in, but the released pressure is plenty high enough that the bearing has to spin.
 

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The mere fact the slave cylinder throwout bearing runs constantly makes me wonder how they last as long as they do. Why did they have to complicate these designs instead of just good logical engineering?

My wife use to work for a 1st gen Serbian engineer who worked in the Apollo program and also the Russian space program. He once told my wife that the American space engineers complicated designs way too much. He said the Russian space designs, though very "unrefined and more simplistic in comparison" had a better durability over the long haul.
 

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That reminds me of the story of how much effort NASA put into designing a ball point pen that worked in zero "g" while the Russians just used a pencil. KISS goes a long way.
 

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The clutch rod spins whether engaged or disengaged. But, thinking it thru with a mechanically (but adjustable) actuated clutch vs the hydraulically actuated that is "not adjustable" but fixed by virtue of engineered position, throw, and rod length yields little difference. But, since the clutch rod dead centers on the diaphragm spring and therefore, no radius (for torque) it then has the possibility of an infinitely tiny point which produces zero rotation. A dab of required grease at the pointed end (to take care of the non-infinite) and a larger dab at the slave thrust end will reduce compression friction especially when the clutch lever is relaxed (ie engaged) and IMO it will rotate little. It is those that do rotate that ruin the slave bearing (spins the piston) and scour the slave walls and R & R is required. I venture that most who do the "slave", R & R, never pull the slave apart so they don't know if it spun or not. If much rotation was expected by BMW engineering that slave bearing would be more robust than it is.
 

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Tourdog said:
The clutch rod spins whether engaged or disengaged. But, thinking it thru with a mechanically (but adjustable) actuated clutch vs the hydraulically actuated that is "not adjustable" but fixed by virtue of engineered position, throw, and rod length yields little difference. But, since the clutch rod dead centers on the diaphragm spring and therefore, no radius (for torque) it then has the possibility of an infinitely tiny point which produces zero rotation. A dab of required grease at the pointed end (to take care of the non-infinite) and a larger dab at the slave thrust end will reduce compression friction especially when the clutch lever is relaxed (ie engaged) and IMO it will rotate little. It is those that do rotate that ruin the slave bearing (spins the piston) and scour the slave walls and R & R is required. I venture that most who do the "slave", R & R, never pull the slave apart so they don't know if it spun or not. If much rotation was expected by BMW engineering that slave bearing would be more robust than it is.
The forward end of the shaft goes through the clutch diaphragm spring and into the engine output shaft. The part that rests in the center of the diapraghm is as large as what rests against the piston bearing, but chamfered, so actually more surface area. The rod never spins against the diapragm spring, even if lubricated. I put a little lube on mine, but next time it was removed there was the normal expected brown "fretting" on the forward end, no rotational movement evident.

When the clutch is engaged (lever out) the piston is pushed back against the piston spring, so the spring is loaded at it's heaviest. That is a pretty decent load on the little bearing.

Yes, I am very surprised that BMW designed in such a small bearing that runs constantly. Unfortunately, there is little room available to make something bigger. The swing arm is right behind the slave cylinder, and the transmission is already remarkably thin for all that is in it. If I were to re-design it, I would change the design of the diapragm spring to allow a much larger bearing to be installed in it (there is room) and add a better pilot bearing in the end of the engine output shaft or eliminate that guide end of the actuation rod. A feature could be added to prevent rod rotation, but then it would still be inside the transmission input shaft for much of it's length, with that spinning when the bike is in motion.

That little bearing in the slave piston is one overworked little dude! Amazing most last as long as they do.

I stongly recommend periodic Preventive Maintenance replacement of the slave! Maximum 60,000 miles, maybe 48,000 or 54,000 service intervals would be safer. Even as much as I rode that would still only be every 18 months to 2 years. A lot longer for most. Shorter for a few.
 

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Makes you wonder if in fact a transverse engine/drivetrain on a motorcycle is not the better design configuration compared to an inline K type configuration. Most engine components are accessible, the exception being maybe valves clustered under the tank. Something to be said for the new K engine heads sticking almost straight forward.
 

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Timely clutch slave discussion

Hi! Long time no post in this forum. Butt, this is the first place I look when I'm in trouble, and I am! :(

Sorry to interrupt your regularly scheduled discussion of clutch bearing theory but I have a practical application type question.

Tonight, on the 60 mile commute home, I sensed the engagement part of the clutch lever was moving closer and closer to the handlebar. By the time I got half way home I had no ability to disengage the clutch. I was shifting by forcing the bike from gear to gear with no clutch. Of course, the challenge was to make if off of the freeway, across the major thoroughfare, down the residential streets and into the garage. Miraculously, I made it without having to come to a total stop! :) Yeah, I had to run a few stop signs but no stop lights!

Now the bike is in the garage, clutchless and I'm clueless what to do to get the bike back to San Jose BMW (60 miles). Is there any temporary addition of fluid that might last long enough to get me to the dealer and, if so, where does that fluid go?

Possibly related to this dilemma is the fact that fluid has been leaking from the boot next to the final drive. It doesn't look like oil and could be brake fluid. I made an appointment to get it fixed next Tuesday.

Any thoughts?
 

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ltcommuter said:
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Is there any temporary addition of fluid that might last long enough to get me to the dealer and, if so, where does that fluid go? The fluid normally goes right into the clutch assembly! Unless a line broke, that is about the only result, if the drain hole has not been drilled. Unfortunately, you probably are looking at a slave cylinder and clutch replacement. There is nothing you can do to make it better. You can add brake fluid, but that will only help you get it going for a short time, and put just that much more fluid into the clutch.
Possibly related to this dilemma is the fact that fluid has been leaking from the boot next to the final drive. It doesn't look like oil and could be brake fluid. I made an appointment to get it fixed next Tuesday.

Any thoughts?
The fluid leaking from the swing arm boots is completely unrelated to any clutch issues, as there is no commonality at all. No way for brake fluid from the clutch actuation system to get there, period. That is transmission fluid if coming from the small boot on the front of the swing arm at the output shaft of the tranny, final drive oil if coming from the boot in front of the final drive. Neither of these is as drastic or as expensive as the slave cylinder failure though.
 

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dshealey said:
> If I were to re-design it,.
Why not use the design from the 1100 RT ?
Mechanical cable actuated. BMW changed to the output cylinder on the 1150 RT. Perhaps the mechanical design takes up to much room.
 

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I don't profess to have the engineering background of David, didn't sleep in a HI Express last night, but have replaced my slave cylinder three times in 120k. I have taken them apart with a friend who designs hydraulic systems for a living and all three have shown significant deterioration of the the rubber/neoprene whatever it is seal. It seems that as it wears it sheds very small balls of material that can accumulate along the seal and eventually create a path for the leak. I have recently obtained some seals he recommended of a different material and will be rebuilding two for future replacement. I have extra seals if anyone is interested.
 
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