Hi,

Any help would be greatly appreciated. New to working on this bike.

Recently purchased a 907. Clutch was in bad shape so I purchased a Barnett Clutch pack. Installed over the weekend with meticulous attentiion to diagram/stack height etc.

When I buttoned it all up there was some serious slipping. Much better than before I put the new clutch pack in, but not really drive able.

What do I check next?

Again, any thoughts or ideas would be much appreciated.

-paul

What stack height number are you using? Should be the same for all later Ducatis with a dry clutch, which I kinda remember to 48.5mm or something like that. I keep the old metal plates so I can mix and match to get the thickest stack possible that stays inside the basket. I am assuming that they indeed are dry, and you didn't get oil on them.

The clutch pressure plate has a triangle on it, and it should be aligned to the screw boss in the basket that has the hash mark on it. If you don't get the pressure plate to seat all the way down, the clutch will slip.

If some one put an extra ball in the pushrod, or too long of a pushrod, the system won't return enough to allow the pressure plate to put enough pressure on the stack. Pull off your slave cylinder and and pressure plate and run a coat hanger wire through the hole to see what is in the stack. Refer to the manual for proper assembly.

And lastly, if the adjusting screw on end of you lever has been screwed in too far, the piston won't be allowed to return to home and vent the system, and you will build up pressure after a few pulls, and the clutch will start to slip. That screw is not for adjusting the lever position. Back it off a few turns to make sure its not holding the piston in too far.

Are you trying to do the quiet clutch modification? If so, confirm that its not interfering.

Happy hunting.
Phil

Thanks for your response. I ran through the list and checked it out on the bike. Notes below

I am using a stack height of 39mm. This is about 2mm higher than the stack that came out--but this makes sense given that the friction pads were totally worn out on the old plates. I checked with the original shop manual and this stack height seems correct.

I am not doing the quite clutch mod.

Regarding the pressure plate--I thought this might be the culprit. So I have it lined up properly with the notched post and arrow etc., but it still doesn't seem to be sitting down all the way. The teeth on the pressure plate only seem to go about halfway down onto the hub. This seems strange b/c the stack height is correct, so I would think that the pressure plate would go further down on the hub. Anything to this I'm not seeing? The plates are all pushed in as far as they can go. . .

Lever seems fine.

Thanks again for all the help--still not working right, though I have now taken all the plates out again. Should I try a shorter stack height so that the pressure plate sits lower on the hub? Any other ideas?

Thanks,

Paul

Hi, FWIW, I had my Barnetts slip , i removed & cleaned with brake cleaner,light sand to remove glazing and never had problem again.

39mm, sounds right. I guess the number I was trying to remember is 38.5mm. I always put in as many plates as i can get into the basket and not come out of basket when the clutch is pulled in.

Did you start with 2 steel plates in the basket first?

Take a few plates out and confirm that the pressure plate has full travel.
-If it doesn't, take out the pushrod and see if that changes anything.
- use modeling clay, or even a piece of paper to put between the pressure plate and basket to see where there is interference.

The stack height should 38mm ± 2mm. I found this article on setting up Ducati dry clutches a few years ago. Here it is below, it might be helpful in sorting out your problem.

Ducati Clutch Tuning Voodoo
submitted by Larry Kelly

Clutch Tuning Voodoo

Clutch engagement problems are quite common, but solving them often requires a fair amount of trial-and error work.
Usually, an uneven take-up or excessive slipping signals the need for a clutch pack replacement, often just caused by normal wear loss of the friction material on the plates. The mileage between replacements has a very wide range, anywhere between 3,000 and 30,000 miles, depending upon the amount of city riding and the rider’s launch style. If the clutch type is a slipper, it’s normal for the friction material to wear-out sooner since it’s function is to allow the plates to slip past each other under high engine-braking loads during downshifts. Some friction materials do better than others regarding wear and engagement smoothness, just like brake pads.

Sometimes engagement problems begin after you’ve just replaced your worn-out stock clutch components, upgraded to an aftermarket clutch or changed to a slipper clutch.
The key to smooth engagement is controlling the frictional force developed between the smooth plates (that are driven by the engine clutch hub) and the plates that contain friction material (that drive the rear wheel through the clutch basket.)

The amount of force developed between these plates is controlled by the stiffness of the clutch springs, specifically by the amount of preload on these springs. When the clutch is fully engaged, the friction force developed between the plates needs to be greater than the engine’s applied torque to prevent slip. About 430 lbs is needed on a stock superbike.
When you pull-in the clutch lever, the hydraulic pressure applied to the slave cylinder overcomes the spring’s preload and progressively reduces the force pushing the plates together until they begin to slip. During this time the dished plate(s) in the stack act to provide a progressive reduction in the inter-plate force as the plates separate a few millimeters and you get full disengagement.

When you engage the clutch the opposite occurs. The reduced hydraulic pressure on the slave cylinder allows the push-rod to move the spring-loaded pressure plate toward the plate stack (a millimeter or so) until the plates begin to touch. Keep in mind that when you move the lever you are changing the POSITION of the pressure plate. You have only indirect control over the forces between plates.
The forces between plates is controlled during this transition (between disengaged and fully engaged) by a dished plate that is included in the stack to smooth this transition. This plate acts as a spring (pushes back with a force) when it gets flattened between adjacent plates by the movement of the pressure plate.
So, the force pushing the plates together first come from the smaller force produced by flattening the dished spring plate, and later, a much greater force produced by the preloaded clutch springs.

The higher the height of the clutch pack, the greater the clutch spring preload. So, as the clutch pack friction material wears-out, the pack height gets shorter, until the force between plates is insufficient and the clutch slips, at first under high torque conditions such as at launch, and later even when the lever is not pulled at speed. Time for a new clutch.
This is also the cause of the annoying phenomena of clutch “judder” such that when you release the lever, and while the spring plate is being compressed, the clutch springs can’t develop a sufficient force to prevent slipping so the plates slip, grab for an instant (causing vibration-induced slip,) grab, slip and so on, until the slipping stops as the engine torque is reduced when the bike acceleration eventually drops-off.

Here’s the Physics behind it. The friction force developed between two surfaces depends on whether the surfaces are sliding past each other or not. For a given amount of force pushing any two surfaces together, less frictional force will develop between sliding surfaces, than between surfaces that don’t. Once surfaces are together it takes more force to get them to slide than to keep them sliding. Once they begin to side, however, they’ll keep sliding unless you push them together harder.
It’s these alternating higher-lower friction forces that cause the vibration that you perceive as judder. Sometimes adding a second spring plate to the pack will help to damp-out certain vibrations, so Ducati specifies a different number of flat plates, dished plates, plate thickness and stacking sequence for different models. The common spec however is stack height. Ducati clutch packs are stacked to 38mm ± 2mm.

Here’s some examples:
Haynes Manual: 748, 916, 996
7 friction plates - one curved plate with two friction surfaces
Minimum friction plate thickness = 2.8mm
2.0mm plain plate #1 2.0mm plain plate #2 3.0mm friction plate #1 1.5mm dished plain plate (convex side facing toward you) 3.0mm friction plate #2 2.0mm plain plate #3 3.0mm friction plate #3 2.0mm plain plate #4 3.0mm friction plate #4 2.0mm plain plate #5 3.0mm friction plate #5 2.0mm plain plate #6 3.0mm friction plate #6 2.0mm plain plate #7 3.0mm friction plate #7 2.0mm plain plate #8 pressure plate (line up marks)
38.5mm plate stack height

Haynes Manual: 916SP, 916SPS, 996S, 996SPS
8 (thinner) friction plates - two curved plates with one friction surface each
Minimum friction plate thickness = 2.3mm
2.0mm plain plate #1 1.5mm dished plain plate #1 (convex side facing toward you) 2.5mm friction plate #1 1.5mm plain plate #1 2.5mm friction plate #2 2.0mm plain plate #2 2.5mm friction plate #3 2.0mm plain plate #3 2.5mm friction plate #4 2.0mm plain plate #4 2.5mm friction plate #5 2.0mm plain plate #5 2.5mm friction plate #6 2.0mm plain plate #6 2.5mm friction plate #7 1.5mm plain plate #2 2.5mm friction plate #8 1.5mm dished plain plate #2 (convex side facing away from you) pressure plate (line up marks)
38.0mm plate stack height

Ducati Service Manual: 998
6 friction plates - one curved plate with two friction surfaces
Minimum friction plate thickness = 2.8mm
2.0mm plain plate #1 1.5mm dished plain plate (convex side facing toward you) 2.5mm plain plate #1 1.5mm plain plate #1 3.0mm friction plate #1 2.0mm plain plate #2 3.0mm friction plate #2 2.0mm plain plate #3 3.0mm friction plate #3 2.0mm plain plate #4 3.0mm friction plate #4 2.0mm plain plate #5 3.0mm friction plate #5 2.0mm plain plate #6 3.0mm friction plate #6 1.5mm plain plate #2 2.5mm plain plate #2 1.5mm dished plain plate (convex side facing toward you) pressure plate (line up marks)
38.0 mm plate stack height

Stack Height
A too-high overall thickness of the plate stack will cause drag between plates when the clutch is disengaged making it difficult to select neutral when the bike is stopped.
The last 2mm steel plate can be interchanged with a 1.5mm curved plate facing away from you if you want to adjust the stack to get the 38mm stack thickness, or if you want a more progressive, soft clutch engagement. A commonly-used substitution that adds an additional spring plate to the stack.
Any of the steel 2mm plain plates can be exchanged with 1.5mm plain plates to reduce stack thickness or increase stack thickness as needed to achieve your desired overall height. You will see the need for this as friction plates wear, so keep your steel plates from pervious clutch replacements as spares to be used as height adjustments later. The 2mm and 1.5mm steel plates only need replacing if they’re scored or warped.

yeah, I'm one of those ST riders who jumped on the quiet clutch bandwagon 7 years ago, and haven't looked back since. Never heard of any problem from this. I have 15k on my current clutch, with the quiet clutch mod. Did it on my 98 ST2, and then my '02 ST4s. No issues yet.


Cheers, Phil

Morning All.

Is the clutch mod a matter of restacking the plates that are there so a friction plate is at the bottom, or is there a little more to it than that? It seems to be a popular mod for all Ducati's. Just thinking it might be worth the effort of doing the job while the bike is parked up and in bits, or at least having a look.

Cheers.

Nick.

The quiet clutch mod uses a spare friction plate, usually bent up a bit, to offer a small amount of friction between the basket and the hub so that the whole stack is simply preloaded, instead of accelerating and decelerating with every pulse of the pistons. You need an extra friction plate (or two) and put them into the basket first. Then you install the rest of the stack same as you would otherwise. Works like a charm. Ca. Cycle works (as best I can tell) developed the idea and sold a separate pre-bent plate with their kits for a while. The online community discovered you don't need their special part, and just bent up a spare friction plate from our last clutch upgrade.

Does not work with the previous version of the clutch on the 750/906 Paso, Sport or Pantah. Works great on all dry clutch Ducatis from '91 on (as best I know).

Do a web search for Quiet Clutch Mod, Ducati, and you will find a lot of info. Ducati.MS will be the bulk of your info, or the ST2 owners site on Yahoo groups. (that was a great site 2000 - 2010, lots of participation and some really cool mods, Really fell off when they stopped making the ST)

Cheers, Phil

The spare friction plate is bent in two places on the edge of your work bench so you are basically making a warpy washer out of it, but its only 4-5mm high if you lay it flat on the bench after bending. It becomes a bit of spring. Since you install it before any of the metal plates, it fills up the empty space between the metal plates and the bottom of the basket and puts some friction on the back of the first steel plate that never had anything touching it before. It does not affect your stack height, or your clutch function.

Cheers, Phil

...a quiet dry clutch...and simple enough to achieve, definitely give this a go
I fitted the closed clutch cover back on the bike years ago, if it works I will fit the vented cover back.
no matter what anybody says, desmo and dry clutch should always be kept on the ducati design