749 Bucci/DP slipper clutch slipping on takeoff? - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 9 (permalink) Old Aug 24th, 2018, 12:48 pm Thread Starter
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749 Bucci/DP slipper clutch slipping on takeoff?

Hey everyone,

I've got myself a 2003 749 Biposto (allegedly) that is now a Monoposto, with a Bucci/DP slipper clutch. Bike is pretty new to me, I guess I've had it for a few months? Its been perfectly well behaved until this morning. I went to let out the clutch and it slips a lot when starting off. It does not slip under acceleration, and it otherwise slips properly when it is supposed to slip.

I bled the clutch a few weeks ago and it has been fine until just this morning.

I've got the installation guide for the clutch, but it offers precious little info regarding troubleshooting and adjustment.

Clutch pull feels normal, but engagement is pretty close to initial lever pull, e.g. pretty far out. It was that way before and after being bled.

I guess what I am after is if there is anything I can do to adjust it before I leave my office this evening. Ill pull it apart this weekend and check stack height and everything, but first I've got to ride it 25 miles over a mountain. I have every tool imaginable at work, but I don't imagine pulling the clutch totally apart in the parking lot would be a great idea.

'03 Ducati 749
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post #2 of 9 (permalink) Old Aug 24th, 2018, 1:36 pm
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Clutch slippage under acceleration is somewhat hard to detect.The accepted standard is to apply full throttle in top gear and check for slippage so start there to confirm excesive worn plate thickness..Slippage during first launch of the day may be somehow affected by the cold if it doesn't occur during subsequent launches.
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post #3 of 9 (permalink) Old Aug 24th, 2018, 1:46 pm
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Quote:
Originally Posted by Alabamarama View Post
Hey everyone,

I've got myself a 2003 749 Biposto (allegedly) that is now a Monoposto, with a Bucci/DP slipper clutch. Bike is pretty new to me, I guess I've had it for a few months? Its been perfectly well behaved until this morning. I went to let out the clutch and it slips a lot when starting off. It does not slip under acceleration, and it otherwise slips properly when it is supposed to slip.

I bled the clutch a few weeks ago and it has been fine until just this morning.

I've got the installation guide for the clutch, but it offers precious little info regarding troubleshooting and adjustment.

Clutch pull feels normal, but engagement is pretty close to initial lever pull, e.g. pretty far out. It was that way before and after being bled.

I guess what I am after is if there is anything I can do to adjust it before I leave my office this evening. Ill pull it apart this weekend and check stack height and everything, but first I've got to ride it 25 miles over a mountain. I have every tool imaginable at work, but I don't imagine pulling the clutch totally apart in the parking lot would be a great idea.
The problem with the OEM slippers is that there is really not a lot of adjustability... in your case however that is a good thing as there are very few culprits which could be the cause. Having lived with the OEM slipper on my 748R the Spider Spring would be the very first thing I would check whenever something didn't feel right with the clutch, as it provides the spring force for the slipper activation itself. They would constantly fracture, and when they did, there was far less force required to activate the slipper function. However, you would notice it across the board, starting off, accelerating, aggressive downshifting, etc. So if this is happening only when starting off, it is probably not that. You should still check it, as, like I said, the ones on my clutch would snap at least once per season. If you are going to continue to run that clutch, it is probably a good idea to get spares.

Unfortunately, you are probably going to have to pull the clutch stack and inspect the driven (flat) and drive (friction) plates. Check the stack for proper height, and then inspect the plates for wear.

That is pretty much all I can think of... sorry I don't have a better answer for you.
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post #4 of 9 (permalink) Old Aug 24th, 2018, 2:58 pm Thread Starter
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Thanks for the quick replies!

I didn't notice much in the way of adjustment, but I did make sure the bolts were tight. I accelerated hard in 3rd to get around some joker on my way in and didn't notice any slippage. Its pretty pronounced when I let out the clutch, to the point where it is difficult to get the bike moving. If it did that while in gear and rolling I would think I wouldn't be able to ride it at all.

Ill definitely inspect the Spider Spring tomorrow though.

The bike sat in a shed under a cover for the better part of a decade so honestly I am surprised its been as trouble-free as it is.

'03 Ducati 749
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post #5 of 9 (permalink) Old Aug 24th, 2018, 3:12 pm
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I have a Yoyodyne slipper which is basically the same design and slippers are very sensitive to stack height. As a result every so often I have to swap out a 1.5mm steel plate with a 2.0mm plate: this restore the proper stack height and compensate for clutch plate ware which is noticeably higher than under regular use. I switched to the race plate setup that add 2 sintered plates and helps as you have more surface.

The stack height needs to be right between 1mm and 1.5mm greater than the drum height (call it "preload") to allow the pressure plate to exercise enough pressure on the clutch but at the same time allow the drum to lift and unseat the plate when you get excessive engine braking. If the preload is too low the pressure plate doesn't exercise enough pressure and the clutch slips, if it's too high the drum doesn't lift the pressure plate and the slipper action doesn't take place.

When I get close 1mm in preload I replace one of the steel plates to add the 0.5mm that wore off.

My Yoyodyne has an access point in the pressure plate to evaluate stack height against a baseline and evaluate whether a thicker steel plate needs to be added.

See if this helps -> https://drive.google.com/file/d/0B1e...ew?usp=sharing

Here's the instruction of the Bucci if it helps -> https://drive.google.com/file/d/0B1e...ew?usp=sharing

The other thing is check the adjustment of the master and confirm that it properly release fluid pressure when you release it. I think at one point I was messing with it and dialed out all the play it had. As a result the plunger in the master wasn't retracting enough and pressure from the circuit was releasing back slowly.
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Last edited by ZetaTre; Aug 24th, 2018 at 3:21 pm.
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post #6 of 9 (permalink) Old Aug 24th, 2018, 4:05 pm
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Stock or aftermarket clutch lever??
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post #7 of 9 (permalink) Old Aug 24th, 2018, 4:47 pm Thread Starter
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ZetaTre, thanks for the literature! I had the Bucci installation instructions, but that Yoyodyne instruction is super helpful

Xracer, I believe it has the stock levers. Silver cast aluminum w/ only reach adjustment. The bike has so much aftermarket stuff on it that it can be hard to tell sometimes.

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post #8 of 9 (permalink) Old Aug 24th, 2018, 4:54 pm
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Quote:
Originally Posted by Alabamarama View Post
ZetaTre, thanks for the literature! I had the Bucci installation instructions, but that Yoyodyne instruction is super helpful
I somehow had some thicker steel plates because I think the race setup comes with 1.5mm and the street is 2mm. But in case that's your issue Yoyodyne sells them; if it's the spider spring you can also call them up and see if theirs matches yours...

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post #9 of 9 (permalink) Old Aug 29th, 2018, 9:17 pm Thread Starter
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Hey folks,

It took a while but I am back with an update

ProphetPVD you were absolutely correct in that the spider spring is broken (see 2:45 and 8:15 positions)



All in all, the clutch looks like its had a tough life. Sitting under a cover in a shed for 5 years certainly didn't help matters either.







So may try shimming it and replacing the spider spring to get me until October-ish when the bike will be off the road for the winter, but that lot will likely need to be replaced. Stack is 35.5-35.6mm, which looks on the low end of things, and those big gouges in the friction material aren't inspiring a lot of confidence.

Thanks to everyone for all of the help!

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