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Clutch randomly engages


Ceritoriari

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I recently acquired a 2007 vfr800 abs, with at least 32k miles (the odometer inconsistently tracks miles) and I recently noticed an odd problem.

 

When I'm at a stoplight, sometimes I rev up to 9-10k when in first gear with the clutch lever pulled completely in (like to launch or wheelie, or sometimes just for fun revs) and sometimes when I do this, the clutch will engage randomly for a split second which causes an ungodly lurch forward. I'm not really sure what's going on with it, it's done this ever since I started doing revs at a stop, I had the hydraulic clutch flushed (unrelated-but because the old fluid was dirty/milky) and it's had this problem before as well as after the flush, does anybody have any idea what's going on?

 

A second (possibly unrelated?) problem I sometimes have is when I'm banging through gears, I'll get to 3rd or 4th gear, up to about 9-10k RPM, and the bike will seem to disengage the clutch and throw me into redline, I'll let off the gas and go back on it then I'm fine.

I'm not really sure what's going on with this bike, but I was hoping somebody could help me.

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What you're doing is not good for it..... you need to calm down, but carry on, it's your bike.  Sounds like you have a couple of things going on.... clutch is grabbing and clutch is slipping.... I'd guess there is some notching of the clutch basket not allowing the clutch plates to freely move.... it's all the abuse, for the sake of your bike, change your bad habits.  Take the clutch apart and be ready to get yourself a new clutch basket and a new clutch pack.

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4 hours ago, raYzerman said:

What you're doing is not good for it..... you need to calm down, but carry on, it's your bike.  Sounds like you have a couple of things going on.... clutch is grabbing and clutch is slipping.... I'd guess there is some notching of the clutch basket not allowing the clutch plates to freely move.... it's all the abuse, for the sake of your bike, change your bad habits.  Take the clutch apart and be ready to get yourself a new clutch basket and a new clutch pack.

Thank you for the insight, they're not things I do regularly, but when I'm really cookin it is when I notice problems, I'll look into changing the clutch if I start noticing problems in normal riding

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My bet is that all of those Revs are giving the Clutch Slave Cylinder a really good shaking transmitted by way of the clutch pushrod, and that shaking is transmitted up the line (via the incompressible hydraulic fluid) to the Clutch Master Cylinder.  So it becomes a "liquid hammer" situation that is strong enough to drive the hydraulic fluid past the rubber sliding seal in the Clutch Master Cylinder.  Which allows the clutch to grab as you described.

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1 hour ago, GreginDenver said:

My bet is that all of those Revs are giving the Clutch Slave Cylinder a really good shaking transmitted by way of the clutch pushrod, and that shaking is transmitted up the line (via the incompressible hydraulic fluid) to the Clutch Master Cylinder.  So it becomes a "liquid hammer" situation that is strong enough to drive the hydraulic fluid past the rubber sliding seal in the Clutch Master Cylinder.  Which allows the clutch to grab as you described.

And given that the previous clutch fluid flush was described as "dirty/milky"! Who knows what the state of the pistons, seals and cylinders are.

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  • 2 weeks later...
On 6/17/2020 at 4:31 PM, GreginDenver said:

My bet is that all of those Revs are giving the Clutch Slave Cylinder a really good shaking transmitted by way of the clutch pushrod, and that shaking is transmitted up the line (via the incompressible hydraulic fluid) to the Clutch Master Cylinder.  So it becomes a "liquid hammer" situation that is strong enough to drive the hydraulic fluid past the rubber sliding seal in the Clutch Master Cylinder.  Which allows the clutch to grab as you described.

Oh, interesting. I don't know a lot about how that works so that's good to know

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On 6/17/2020 at 6:33 PM, Grum said:

And given that the previous clutch fluid flush was described as "dirty/milky"! Who knows what the state of the pistons, seals and cylinders are.

Another good point, I should look into those too

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Mercy!!! what you're doing is exactly what a oil cooled clutch was designed for so rev it up and have a wheelie nice day... there is no good reason to change your habits... what might be happening is hot spots which is normal when you sit at a light with the bike in gear and the clutch lever is holding the plates open... have a look at steel plates the next time you have the cover off and note any blue marks like the ones you see on my RC45 due to its racing intent use of a slipper clutch...

 

PressurePlates2.jpg

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On 6/17/2020 at 7:13 AM, raYzerman said:

What you're doing is not good for it..... you need to calm down, but carry on, it's your bike.  Sounds like you have a couple of things going on.... clutch is grabbing and clutch is slipping.... I'd guess there is some notching of the clutch basket not allowing the clutch plates to freely move.... it's all the abuse, for the sake of your bike, change your bad habits.  Take the clutch apart and be ready to get yourself a new clutch basket and a new clutch pack.

Negative... notch basket will not the cause plates to grab and slip like you're guessing... hot spots and unserviceable master cylinder will...

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On 6/26/2020 at 11:41 PM, BusyLittleShop said:

Mercy!!! what you're doing is exactly what a oil cooled clutch was designed for so rev it up and have a wheelie nice day... there is no good reason to change your habits... what might be happening is hot spots which is normal when you sit at a light with the bike in gear and the clutch lever is holding the plates open... have a look at steel plates the next time you have the cover off and note any blue marks like the ones you see on my RC45 due to its racing intent use of a slipper clutch...

 

PressurePlates2.jpg

A wheelie nice day hahahaha that's awesome. This is really good advice too, I've gotten lots of good ideas and things to look at from replies to my post. It sounds like a number of things need to be done.

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