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Here is an odd one. Clutch works fine around town, and always feels the same. But when I did a hundred miles the other day, the lever went dead after about eighty miles of highway riding. A couple of pumps brought it right back. And then on the way home, it did the same thing. And again, a couple of quick pumps brought it right back. Fluid level is fine, so I know I am not losing any. Stainless line installed last season. I am running a Yoyodyne slave.

Could it be as simple as moisture in my fluid?

Any ideas?

Thanks so much for reading.
 

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I would bleed it first but your description sounds like a bad master cylinder, if you get no air in the bleeding then either the seal in the master is not holding pressure or you clutch is falling off. You usually notice when the clutch falls off.
 

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Could it be as simple as moisture in my fluid?
Yes, I believe your problem is boiling fluid. Over time the fluid collects moisture from the air. Since water is heavier than brake fluid, it eventually ends up it the bottom of the slave cylinder. Once the bike gets hot, the water will boil and create air (steam) pockets—this gives the feeling that the clutch lever has gone soft. Once the bike (and fluid) cools down, the stream returns to a liquid state and you have clutch pressure again.

The engine temperature at the slave cylinder location can easily reach 212 degrees F (the boiling point of water), and nearby small pockets of water, as they boil, introduce water vapor in the line that causes behavior just like air in the line does.

The only solution to this is to flush your system to get rid of the water-saturated fluid and the water droplets completely. That means getting rid of all the fluid in the reservoir and in the lines, and particularly make sure that any water droplets that have puddled in the slave cylinder are flushed out. This usually requires removing the slave and inverting it to assure that all water is removed down in the lowest point of the slave. Use compressed air to assure that the slave is completely dry before reinstalling. Use DOT 4 fluid from a sealed container and make doubly sure that the reservoir cover is sealing properly.
 

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Discussion Starter #5
Thanks, Guys!!

I never knew tht the slave got tht hot. Now it is all making sense.

Maybe I should rebuild the master while I am at it. Unfortunately, Yoyodyne refuses to sell me a new seal for the slave. But it is not leaking, so I should be good.

By the time I am done, there will not be a part on this bike that I have not updated, LOL.
 

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Take a look at your clutch pushrod, make sure it's not wearing [spinning,boring into the pressure plate bushing or slave] but do the fluid first. It's rare but it does happen.
 

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In almost 20 years of doing Ducati service professionally I have seen 1 yoyodyne slave failure, it was a pushrod that drilled a hole in the cylinder piston so hardly the fault of the slave.

You state it got a new line last season so we know you changed fluid then, I do not see the fluid going bad in that time frame. Yes the slave gets VERY hot a friend with a infrared camera took photos of his ST2 and the slave was hotter than the rest of the motor around it (heat sink?). Either way this is normal to be hot and it is NOT normal to have either a bad yoyodyne slave or 1 year old fluid to be that bad so I would go after the clutch master. they also are pretty reliable units so I would not be afraid to but a used unit but be careful not to pay new unit price for a used one on ebay.

You might be able to buy a rebuild kit for yours but if the bore is damaged it is a waste of money/ time and the cost for a good used/ new one should be not bad.
 

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If you wind up replacing the clutch master, I recommend pricing them at one of the known Ducati vendors like Motowheels - it's nice to support businesses who support us.

You can comparison shop at www.oppracing.com if you want to verify the price for a new part.... Looks like the coffin style is $100, and the gold remote reservoir style (without the reservoir) is $145.

If you're not picky you can also convert to a semi-radial master from any of the new bikes. You will frequently see masters from 1098/1198 etc for sale after someone upgrades to an RCS master. They will go straight on with little fuss. If you think you'll want to match the brake master, be warned that it will turn into quite the project as you'll need to move the throttle cables around.
 

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Take a look at your clutch pushrod, make sure it's not wearing [spinning,boring into the pressure plate bushing or slave] but do the fluid first. It's rare but it does happen.
I second this one. Remove the slave and the operating rod. Broken rod can cause this and eventually other issues.

Of course, fluid is an easy and good place to start.
 

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So, When I drove my ST2 on long trips, and getting zesty on back roads, occasionally the clutch lever would pull in with ZERO resistance. Huh? The next pull was ok.. huh?

The only thing I ended up doing was removing the clutch PP, and along with it, came the rod. Huh? I thought? So it appears after many a mile, the clutch dust gets everywhere, including the "derby-hat" tip that rides in the T.O. bearing. I cleaned all this up, so that the rod would slide free of the derby-hat, and the issue never returned.

I assume the rod was spinning sometimes (or all the time?), creating the unwanted heat in the slave...

That's my story an' stickin' to it.
 

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Take a look at your clutch pushrod, make sure it's not wearing [spinning,boring into the pressure plate bushing or slave] but do the fluid first. It's rare but it does happen.
Doesn't the pushrod spin when the bike is in neutral, then stops spinning when you pull in the clutch lever?
 

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Doesn't the pushrod spin when the bike is in neutral, then stops spinning when you pull in the clutch lever?
The pushrod shouldn't spin really ever. I was worried about this with with mine ('95 900ss), and did some tests. I put little dots on the pressure plate, the throwout bearing, and the "pushrod cap", so I can see when they are spinning. When the clutch lever is released the pushrod pulls back and there isn't enough friction between the rod and the cap to make the cap (aka pressure plate bushing, I think) stop spinning. So, the cap and throwout bearing spin almost as fast as the pressure plate. However, the slightest pressure on the clutch lever and the pushrod contacts the cap. This makes the cap stop spinning and the throwout bearing spins with the pressure plate.

Conclusion: I cannot know for sure that the pushrod is NOT spinning, because I can't see it. However, since the cap stops spinning when the pushrod applies pressure I assume it is not. The cap spinning when the pushrod is NOT applying pressure does NOT mean that the pushrod itself is spinning.

If I'm crazy, somebody please chime in.
 

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If I remember correctly there is actually nothing to prevent spinning so under the right conditions the rod might spin . Dirt build up, low clutch stack height, dragging bearing ?
 

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If I remember correctly there is actually nothing to prevent spinning so under the right conditions the rod might spin . Dirt build up, low clutch stack height, dragging bearing ?
I can grab mine and spin it with my fingers, but only when it is clean/dry. There is a fair bit of resistance. It doesn't spin freely, for sure. I bet it spins a bit right when it first pushes against the pressure plate, but certainly not at full engine rev speed for very long. The seals aren't designed for that.
 

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I visited my local Ducati shop today and asked about this dilemma, in an attempt to discern uninformed advice.

The pushrod should and can spin slightly. Lube should be applied to the recess in the slave cylinder, and at the opposite end inside the clutch control pin (lubricate and corrosion prohibitor). Pushrod spin inside the clutch control pin isn't unusual. There is no routine replacement period for the throw out bearing due to individual conditions (i.e. exposed/enclosed cutch pressure plate.
 
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