Phantom Clutch Actuation... - MVAgusta.net
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post #1 of 21 (permalink) Old 02-08-2009, 05:08 PM Thread Starter
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Phantom Clutch Actuation...

Okay, so this is probably going to sound a little weird, but bear with me...

Figured this out one day on a trip up to Mt. St. Helens (beautiful ride btw). On a long straight I was resting my clutch fingers a little heavily on the clutch lever and noticed it started to disengage. Let me rephrase that... The lever began to travel, but the clutch remained engaged. I wasn't actually applying pressure on the lever (not intentionally anyway), but with just the weight of my fingers, and maybe a LITTLE bit of effort, the lever moved. After playing around with this theory, I noticed that if I moved the lever very slowly, even traveling at 60+ mph in 4th gear, I could effectively fully close the lever to the bars without any change in clutch engagement.

Now I have a theory on this, but I'm no mechanic, and I'm not sure how this will hold up, but here it goes:

Understanding that a hydraulic system operates by moving fluid from one reservior to another, translating lever movement through pressure to move some mechanism at the other end, is it possible to move the fluid from one res. to another with low enough pressure to not effectively operate the hydraulic system?

I could literally ride with the lever at the bars, and there was no change in engine response. My speed remained the same, and I could accelerate or decelerate with the same effect as normal, no obvious clutch slippage.

Maybe this is true of all hydraulic clutches, and I'm getting excited over nothing, but I thought it was pretty strange and wanted to clarify.

Any thoughts?

"...and as I shifted into 6th, the engine screaming ferociously beneath me, I stared into the face of god." - Johnny

'05 MV Agusta Brutale S 750 (Nero)
'05 Suzuki GSX-R 600
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post #2 of 21 (permalink) Old 02-08-2009, 05:18 PM
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It's not possible to move fluid and have no actuation. Instead of imagining a reservoir on the other end, imagine filling up a piston, even very slowly, it should still end up being pushed by the fluid. I'm not sure as to why this is happening to you, however.

If you pull on the lever normally, can you engage and disengage the clutch?
If yes, I'd figure that something needs adjusted, probably down in the clutch-area.

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post #3 of 21 (permalink) Old 02-08-2009, 05:26 PM Thread Starter
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Yeah, under normal operation everything works fine.

Although now that you mention it, I have noticed that if I am downshifting through several gears and use the clutch for engine breaking, if I don't let the clutch fully engage between gears (i.e. let the lever out to half-engagement then pull it back in and downshift), it seems to shorten the usable range of travel associated with my clutch position. It kind of builds up pressure into a smaller and smaller area until I can fully engage or disengage the clutch in an area of maybe 1/4 of full lever travel. After that though, when I let the clutch fully engage again, everything goes back to normal.

Like I said, if I operate it normally, I don't notice any problems. No slippage, no half engagement, no skipping / missing / or popping out of gear.

"...and as I shifted into 6th, the engine screaming ferociously beneath me, I stared into the face of god." - Johnny

'05 MV Agusta Brutale S 750 (Nero)
'05 Suzuki GSX-R 600
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post #4 of 21 (permalink) Old 02-08-2009, 05:33 PM
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Something's amiss

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post #5 of 21 (permalink) Old 02-08-2009, 07:15 PM
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I'm not too up on the clutch configuration and what-not regarding the innards of an MV, but if you've got a few hours, drain the oil and pop off the right casing and check out the clutch discs. See if they match what the manual specs say they should using a micrometer. Maybe your clutch is wearing strangely or something?

But from the way you describe it, I'd be led to believe that it's not that, instead it's the hydraulics... somehow. Definitely need one of them more tech savvy people to chime in regarding this.

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post #6 of 21 (permalink) Old 02-08-2009, 09:12 PM
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There are rubber seals inside your clutch master and slave cylinders. If those seals are worn, groved, degraded or installed incorrectly, the problem you describe can occur. Also if there is air in the sytem it can cause similar symptoms. Since you are not a mechanic...self described...I'd reccomend taking the bike to your dealer/shop and have them replace the clutch fluid, bleed thasystem and test it for degraded psiton seals.
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post #7 of 21 (permalink) Old 02-08-2009, 09:29 PM Thread Starter
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That's what I was wondering, if maybe MV has some abstract clutch / hydraulic config dissimilar to most japanese bikes that might allow for this phenomenon. I know it sounds weird, and I would never have guessed it would function like it does. All my other bikes have cable clutches so I have nothing to compare to. My Brute has only about 2k miles, so I'd be suprised if there's any excessive clutch wear, unless something's seriously wrong.

I might have to crack it open and take a look at the plates anyway though, unless I get a more definitive answer.

Anybody taking a ride soon want to test a theory?

I should elaborate on "slow lever movement." To initiate this scenario, the clutch lever must be pulled in very gently over a 4-6 second period while maintaining throttle position (under load of course). Obviously you'll know right away if it's happening or not, as a normally functioning clutch would cause slippage and your rpm would rise. Somehow my r's are stable. It's also strange how it requires very little effort. The lever seems to be guiding itself in, and I can feel the resistance to move lessening slightly as it progresses. If I give it too much assistance, it functions normally and will begin to disengage.

??

"...and as I shifted into 6th, the engine screaming ferociously beneath me, I stared into the face of god." - Johnny

'05 MV Agusta Brutale S 750 (Nero)
'05 Suzuki GSX-R 600
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post #8 of 21 (permalink) Old 02-08-2009, 09:35 PM Thread Starter
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Quote:
Originally Posted by silentservice703 View Post
There are rubber seals inside your clutch master and slave cylinders. If those seals are worn, groved, degraded or installed incorrectly, the problem you describe can occur. Also if there is air in the sytem it can cause similar symptoms. Since you are not a mechanic...self described...I'd reccomend taking the bike to your dealer/shop and have them replace the clutch fluid, bleed thasystem and test it for degraded psiton seals.
Now we're getting somewhere. I planned to mention it next time I take it in.. I do wonder though if it's detrimental to ride it as is. I don't have any problems unless I perform the aforementioned procedure. My next service is at 3750mi. I believe.

I bought the bike used with 1700mi on it. It's was bone stock and supposedly never raced. I don't technically KNOW what the previous owner did with it, but I don't imagine he would have screwed this up, so I guess it's probably an assembly defect.

"...and as I shifted into 6th, the engine screaming ferociously beneath me, I stared into the face of god." - Johnny

'05 MV Agusta Brutale S 750 (Nero)
'05 Suzuki GSX-R 600
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post #9 of 21 (permalink) Old 02-08-2009, 10:02 PM
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You have air in the system.
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post #10 of 21 (permalink) Old 02-08-2009, 10:13 PM
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The worst thing that can happen in the conditions you list would be that you would be unable to disengage the clutch to shift gears. "Blip" shifting works but isn't that healthy fo rthe gearing. Refresh the fluid and bleed the system and see if that restores a "hard" lever feel.
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