Clutch grab - another one!! - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 05-25-2011, 12:43 AM Thread Starter
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Clutch grab - another one!!

So, just to be sure. Drilling out the clutch hub will allow cold oil to flow outward and in between the friction plates sooner, so they will not stick and "grab" making the grinder noise and causing the bike to suddenly lurch forward when letting out the clutch in first gear - right?. My plans are to probably do this but keep the existing clutch springs, steel plates and friction plates bacause they are within spec.

Some have suggested just swiching to new springs and EBC Kevlar friction plates as the fix while not drilling the hub. Why would doing this stop the "grab"? Wouldn't there still be the same issue with cold oil not flowing between the friction plates if the hub wasn't drilled?

Trying to understand....... thanks!

Deaner
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post #2 of 8 (permalink) Old 05-25-2011, 07:06 PM Thread Starter
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Anybody have some old clutch friction and steel plates they want to part with? I'd like to build a clutch hub wrench.....

Thanks!

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post #3 of 8 (permalink) Old 05-25-2011, 09:01 PM
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Originally Posted by dino750 View Post
So, just to be sure. Drilling out the clutch hub will allow cold oil to flow outward and in between the friction plates sooner, so they will not stick and "grab" making the grinder noise and causing the bike to suddenly lurch forward when letting out the clutch in first gear - right?. My plans are to probably do this but keep the existing clutch springs, steel plates and friction plates bacause they are within spec.

Some have suggested just swiching to new springs and EBC Kevlar friction plates as the fix while not drilling the hub. Why would doing this stop the "grab"? Wouldn't there still be the same issue with cold oil not flowing between the friction plates if the hub wasn't drilled?

Trying to understand....... thanks!

Deaner
From what I understand, the 'coffee grinder' issue is caused by oil not properly/completely draining out of the clutch hub. It is the old, cold oil that is causing the clutch plates to slip during the initial bike warmup. (others can add the technical details). According to Kawasaki, the fix is to drill a very specific series of holes in the clutch hub (see image below). I haven't seen many posts (in the past 3 years) where owners have tried and proved or disproved this as the ultimate fix. Other posts claim that installing a Kevlar based clutch and new heavier springs will solves the problem. While still others claim that the Kevlar solution only lasted 1 year, before the 'coffee grinder' returned.

Bottom line is that I have not seen a formal study that can quantitatively prove that one or the other solution is the right choice. So, you need to research and search the forum to determine what course of action is right for you.

For what it is worth, I've greatly reduce (not eliminated) the 'coffee grinder' using full synthetic motor oil and a good filter. Currently that is Shell Rotella T6 oil and a Bosch 3325 filter (had similar results using Castrol full synth and an OEM filter).

However, if I were to attempt to solve the 'coffee grinder' for good, then I would go with the Kawasaki option of drilling the clutch hub first. It is cheap, easy and hopefully Kawasaki had some good engineers come up with it.



Chris Glennon - Portland, OR
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post #4 of 8 (permalink) Old 05-25-2011, 09:55 PM Thread Starter
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Thanks for the info CG. I seem to be having a mental block on this issue. The biggest problem I seem to have is the sudden "grab" when letting the clutch out - accompanied by the grinding noise. Does the oil flow from the inside of the hub, thru the drilled holes to the outside (by centrifugal force), where the friction plates are? I heard somebody say the holes allow the oil to be flung "off" of the disks, thus allowing them to not slip. To me, the holes allow oil to reach the disks, rather than be flung from it. Or does the oil flow from the outside of the hub, thru the drilled holes, to the inside of the hub?

Maybe I need clutch operation 101 class to get this! I'm thinking I dont fully understand how a clutch works.....
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post #5 of 8 (permalink) Old 05-25-2011, 10:26 PM
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Thanks for the info CG. I seem to be having a mental block on this issue. The biggest problem I seem to have is the sudden "grab" when letting the clutch out - accompanied by the grinding noise. Does the oil flow from the inside of the hub, thru the drilled holes to the outside (by centrifugal force), where the friction plates are? I heard somebody say the holes allow the oil to be flung "off" of the disks, thus allowing them to not slip. To me, the holes allow oil to reach the disks, rather than be flung from it. Or does the oil flow from the outside of the hub, thru the drilled holes, to the inside of the hub?

Maybe I need clutch operation 101 class to get this! I'm thinking I dont fully understand how a clutch works.....
My understanding is that the drilled holes in the clutch hub allow the oil to drain out after the bike is turned off. It is that simple. The cold oil that has collected in the hub causes the 'coffee grinder'. The noise and 'grab' is a result of the clutch trying to squeeze it out of the hub.

In Theory (again, I don't have metrics to prove it):
Clutch hub holes = oil drain out of clutch hub when engine off = no squeezing out excess oil when engine is cold = no 'coffee grinder'


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post #6 of 8 (permalink) Old 06-05-2011, 12:11 PM Thread Starter
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Well, I drilled the clutch and found it to be a fairly easy job, Used a Dremel with a 1/16" bit chucked into it. I can't imagine trying to remove the hub nut without an impact wrench. It worked great, basically was able to hold the hub by hand with a rag and let the wrench do the work.

Friction plates and metal plates looked fine and are within spec.

5 hub springs were in spec as well as far as uncompressed length, but I decided to put new OE ones in anyway. Question: Does a spring lose it's "spring" if it sits compressed for a long time? The bike is a 98' and I'm wondering if the springs degrade over time from sitting compressed.

Replaced the hub nut with a new one and used the Motion Pro hub holder tool and a torque wrench to set it at 96 ft/lbs. Used some durable pieces of flat gasket material to cushion where the hub holding tool touches the hub splines, to prevent damaging them. Worked pretty slick!

At any rate, when I get the new springs and put new oil in, I will hopefully be ready to ride - without the clutch grabbing - we'll see!

Will report back when finished....

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post #7 of 8 (permalink) Old 06-09-2011, 09:53 AM Thread Starter
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It worked!!! No more grabbing, growling or screetching - it's gone!

If the grabbing buggs you as much as it did me - just do the fix - you'll be glad you did!

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post #8 of 8 (permalink) Old 06-15-2011, 09:48 AM Thread Starter
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Stay tuned - it "grabbed" again yesterday - ugh!

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