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Discussion Starter #1 (Edited)
Can I have some insight here? My clutch slave cylinder leaked a bit of brake fluid past the two o-ring seals and contaminated my clutch plates. Seals are replaced, upgraded with an Oberon and I don't think it is leaking anymore but I can see it there and it looks like the plates may be sticking. I looked into it because it had started making noise a few weeks ago when cold, a metal sliding across metal sound, accompanied occasionally by a deeper groaning balls rolling sound from deeper in the engine and closer to the front, but that all gradually went away as it warmed up. Never did that before, this clutch has been quiet as a hydraulic for 10,000 miles.

The sprag clutch has been a pain in the ass for over a year, but only when the temp is below 50F, otherwise hits almost every time 1st try. I have a replacement sprag and flywheel but have been putting off installing it. This might be the deeper groaning noise I hear now when cold, maybe it is rubbing the starter pinion?

Clutch out in Neutral, no sound
Clutch in in Neutral, sound but subtle
Clutch in in 1st 2nd or 3rd, annoying sound similar to non-slipper clutch Ducati's but no jangling noises. When cold, it is much louder and I can feel the bike trying to surge forwards a bit. It was never this way before. It really sounds like friction coming from the plates. I hope the bearings in the slipper have not gone off.

Of course once it is in gear there are no unusual noises and it hooks up fine, better even with the Oberon.

What should I do about this?
 

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A few questions first.

1. what brand and type of slipper?

2. new or used?

3. what is the stack height?

4. what clutch plates (sintered or organic)

5. can you get neutral with the bike running but at a stop?

6. what bore diameter oberon?

then a few coments

1. the 2 o-rings are to keep oil in not brake fluid out so it is more likely the oil seal on the right was leaking oil to let plated get coated.

2. sintered plates as well as worn plates will make noises as they do not like to be slipped any time you are trying to slip such as pulling off.

3. The noise is often a groan and shriek that has the effect of fingers on a chalk board

4. If the starter sprag is slipping on a warm motor (or often) you are damaging the other surfaces that it runs on, the longer you wait the greater chance you will need more parts.

5. Try reducing the slipper stack height by .5mm and see if it improves. New slipper packs will often be on the thick side so it is not uncommon for it to drag a little and your larger bore slave is separating the plates less so it exaggerates the issue. Clutch wear on a track bike with a slipper is much more than a stock clutch so be prepared to adjust your clutch pack more often depending on use.
 

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Discussion Starter #3
The brand is Ducati Performance OEM, circa 1992, installed during a total rebuild by the factory race team in 1998 and never ridden until I got it. @8,000 miles now. All parts inside are Ducati OEM and I have not taken the plates out to examine them.

I can get neutral at a stop, easily when warm.

Oberon sent by Motowheels to fit my bike, dunno size. Noise started prior to new Oberon, and did not significantly change it. I really like the way it works, smaller sweep of the lever and a stronger feel to the pressure point of engagement when taking off from a stop.

Just changed the oil, no little bits of sprag clutch or anything else in it.

Ok, so if the plates are wet with anything, (closed cover always), it came from engine oil and its seal is behind all the plates or do you mean the oring on the rod?
I need to pull the rod all the way out to see if there is another oring on that end.

Well, that seems like the next step is to pull the plates and look inside.

But I don't think oil makes the noise I hear. I recorded it, lemme figure out how to post it.
 

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The brand is Ducati Performance OEM, circa 1992,
There was no Ducati performance in 1992, 2002 yes but in 1992 probably a giacamoto 03R29 model or STM. Ducati performance came from ducati buying out Giacamoto in the late 90's. I will guess a 6 spring design with ramps and balls.

Slipper clutches should be disassembled and maintained yearly for track use so it is probably time. You sound like you may have some high spots causing the noise buut if you have not lubed the ramps and balls or the spider spring ends then check for a broken spider spring as well as wear on the ramps. Look at the plates to tell if they are organic or sintered the sintered plates will be bronze colored material.

If you can get neutral then the hydraulics are not the issue and the pack is separating enough so that points more to a grabbing clutch which may be from high spots or something broken/worn.
Pull it apart and pay attention to order of things, watch for the balls in the inner hub falling out. Inspect plates especially the steels for high spots.

The lipped seal in the input shaft is what keeps the oil out of the dry clutch, inspect it as well as the needle bearing and pushrod for wear. You can see them after removing the pressure plate. Organic plates do not last long in a slipper without wearing to the point of slipping so I would be surprised if they are not sintered. Late 90's you might have seen the ducati performance branded parts sold but often they were re-badged giacamoto either way 8000 miles is good life from a slipper. if you are saying you have gotten that many miles out of the clutch look for tab wear.
 

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Discussion Starter #5 (Edited)
They would have been unused from 1998 until last year when I bought the bike, I did find every other place on the bike that needed lube to be in great shape. I did not think to look inside the slipper clutch which has performed flawlessly and silently until now. I can see parts of the plates, and there is at least one bronze colored one, and the tabs I can see are sharp edged and look new to me.

I know a slipper clutch was originally installed in the bike in April of 1991 after the journalist roasted the standard one trying to get 1/4 mile times for their review. It was my understanding it was directly from their North American race team spares, as was this one installed in 1998.

I don't see any dust in there, I would have expected some with organic plates?

Thinking back, when I did the alternator replacement last year I glopped some bearing grease on the clutch pushrod before shoving it through, I wonder if that is where the wetness on the clutch comes from?

There is no slipping at speed from the clutch.

If there are high spots, then they are everywhere evenly distributed because the sounds are a constant pitch, in gear clutch in when warm.

When cold there is another noise, a deeper vibration that I can see affects the part of the spinning clutch where the the hold down bolts are. That part stutters when it is making that noise (but the sound is not coming from there), it slows its spin momentarily during the noise. This sound comes and goes for almost 2 seconds, and then might not do it for another 2-3 minutes and it does stop completely when the bike is warm and won't do it again that day. This sounds like lube needs to be on something. Ramps and balls you say?
 

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They would have been unused from 1998 until last year when I bought the bike
If the plates were new and un-used then you may just be getting things loosened up a bit as the plates wear in. It is hard to guess a diagnoses over the internet without seeing the problem in action. It does sound like you have sintered plates. These will be more prone to be grabby than an oem pack but are used in slippers to gain longevity of the friction material.

I know a slipper clutch was originally installed in the bike in April of 1991 after the journalist roasted the standard one trying to get 1/4 mile times for their review.
Another reason to never listen to a journalist, they are nothing but salesmen. Putting a slipper clutch in a bike that is having clutch issues is tossing gas on a fire. My 92 851 was a press bike as well and they "ruined" the clutch in that as well. Dry clutches and drag strips are not a good idea but back in the day that was as close to a dyno as they got.

It was my understanding it was directly from their North American race team spares, as was this one installed in 1998.
In 98 it could have been a STM (who I believe may have invented the design) or giacamoto/duc performance snap a photo of what you have. A 748r slipper has been found in other bikes but that would probably not be a 98 IIRC.

It comes apart easy enough just pop the cover off and remove the 6 springs. Then take the plates out and keep them in order inspecting the steels for dots on the surfaces. If you find any surface the steels until flat again. Next remove the clutch hub nut and pay attention to washer arrangement as you remove it (do you see the spider spring or is it a diaphragm style?) Finally hold the hub together while pulling it out by the spring posts careful not to let any balls out.

On a safe surface slip the inner and outer parts of the hub apart and you should see balls and ramps inside. Use a bit of moly paste on the ramps and place the balls in the moly to hold it all together. Put the two pieces together and verify function. Reinstall in the reverse order but add a little moly to the tips of the spider spring where it rubs the hub.

If the clutch is lubed and the plates have no high spots it should be functioning normally. If not I would find someone local that has run dry slippers before and see what they think.
 

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Discussion Starter #9 (Edited)
It doesn't look like I expected inside. Stopping for the moment to ask for opinions on what I am dealing with here. It is marked Ducati, and inside the clutch hub is the Cagiva elephant. Only part number I found is LEM.

Oh, and the dirty sticky look to all the parts is my fault, in my ignorance a few days ago I squirted some carb cleaner in there thinking it would clear out the dust. It just made a sticky mess. The problem of noise existed before I did that, so I have some cleaning to do. The clutch packs actually look new and all of them are steel, the bronze ones look very nice and shiny smooth.

Again, for eight thousand miles this clutch was Absolutely silent, other dry clutch riders all remarked on it.

It almost looks to me that instead of balls and ramps, this uses oil pressure to slipper the clutch. There is an oil seal and passages in the hub which does not come apart any further.

* There is one more thing, the inner most clutch pack ring was stuck to the back and did not come out with the others.

Outside pic with just the cover off, the whole album of 8 pictures is on Photobucket - would you take a look?



Gallery Clutch by Tucscon | Photobucket
 

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That is a standard clutch. The plate you found, was that all the way on the inside? It might be an extra plate added to do the " Quiet clutch" modification. If so, that is probably your noise. It wears the tabs and gets jammed in the basket and rubs the clutch hub.
 

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Discussion Starter #11 (Edited)
It really does look like the standard clutch in my manual. With that sintered ring, the clutchpack measures exactly 36.5mm The gap is so tight a breath of air cannot get through the tabs let alone my thinnest feeler guage. Cleaned up, they look new.

Wish I could see another standard one.

Edit* I have seen one now, mine is different. It does not have a cush drive rubber bumper arrangement inside the clutch hub, but a small oil passage leading from the pushrod through the nut which has a hole that must be lined up with a hollow pin on the hub. I can see that oil goes in there, they were clogged up when I removed it. Oil is going into the hub, albeit it must be a very small amount as I cannot shake any out. When I did the alternator late last year I put a glob of grease on the pushrod tube and shoved it thorough - that is what clogged it up I wonder? In any case, holding it by the spline and trying to twist it has no give that I can tell, I don't see how it is functioning as either a cush drive or slipper. What is inside the hub? It looks very finely made, hand turned metal fitted tightly into the aluminum housing.

As far as the shims it looks like the early 91 instructions as to where the 3.5mm sintered ring goes was used originally.

Thoughts?
 

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Discussion Starter #12 (Edited)
And now for the rest of the story,...

Put it all back together, fired it up, sounded like every other SS from the 90's I have ever heard. Disappointed. Rode two short city blocks down the street and turn around - no sound! Well, just a tiny bit of the plates slipping past each other. Now when I started it up it had not been run for two days, more than long enough to produce that ballsy, groaning sporadic noise that worried me and started this thread. Let me make this clear, the sound that bothered me is NOT the normal sound of every 900SS dry clutch out there, but something rude and never heard on my odd bike before. But that noise did not come back! Rode some more, no rumble and the scratchy slipping sound was even reduced more.

Put the full cover back on, no openings. Dead silent clutch once again. Just like the last 8,000 miles plus. A lack of sound that every Ducati owner, every mechanic and even the old 80 year old Italian duffers at Vintage Bike Night has commented on, usually saying "That has a slipper clutch". And yeah, on the race track I can bang down a gear midturn leaned over without the rear end breaking loose, just like a slipper clutch. I have even f'd up enough to bang down two without using the clutch at all hearing a very loud and peculiar whirling noise like low range or a PTO in a 4x4 for a second or two but no tire skidding. I was too busy screwing up at the moment to pay much attention to the sound but this day has brought it back to mind.

When I bought it I was told it had a slipper clutch from the Ducati Racing team since that was where it came from. Yes, there is more to that story but not on an open forum - at least two people were upset about how this bike came to be "lost" for 25 years,.... and no service records were ever written down on this bike, not one ever.

So, this bike has an unusual clutch hub, the insert into the aluminum housing looks lathe turned and pressed in. The aluminum (which is completely different shaped than stock) has the Cagiva elephant, but no visible marks on the steel. If I had a good bench vise I would put it in it to see if I could apply enough force to get it to twist from the center splines, I bet it would. I understand the rocking/sliding motion that slipper clutches do on ball bearings and ramps but I don't know of any other type of slipper clutch. Does this describe any known to you?

Any speculation as to what is inside this sealed hub that only seems to work when the oil passages to it are not clogged? That really is the only thing I did to fix it, clean those oil holes in the nut and the hub. Any cleaning and scotch brite scratching on the plates is incidental as I was the one who gummed them up only a few days ago. You could smell the stuff I sprayed on was the sticky glom I cleaned off, slightly burnt. I suspect there are large ball bearings inside of the hub instead of cush drive rubber bumpers, and because it had no oil created the noise that worried me.
 

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Sounds interesting!

Did you get a pictures of the inner hub?
Look at the back side of the pressure plate and see if there are any teeth there or if it is smooth. The oem 748r slipper used a similar stock pressure plate that had been machined to have no inner splines (teeth). The giacamoto catalog for the 851/888 racing has a slipper that is not exploded so I can not see whats inside but it also uses an oem style (looking) pressure plate.

The interesting thing would be the hydraulic nature used on a dry clutch I have not seen that before so pictures would be appreciated.

To check slipper function you use a inner hub holding tool and then a socket on the hub nut. You should be able to back torque the hub into separating . Well at least on a normal non-hydraulic hub, thinking of it I do not quite get how a hydraulic dry clutch would work. I do not quite get how the oil would open the pack only on downshifts, I wonder if the oil was only in the hub to keep the internals lubricated, maybe ramps but no balls running on a oil film.

The tabs being tight is why it is quiet, if the basket and plates are fresh I would expect it but if it had thousands of miles it should get noisier.
[quoteAny]Any cleaning and scotch brite scratching on the plates is incidental as I was the one who gummed them up only a few days ago. You could smell the stuff I sprayed on was the sticky glom I cleaned off, slightly burnt.[/quote]

If the lube got onto the plates it may have been as much of your noise as the friction plates would grab and slip before being fully clamped.

I suspect there are large ball bearings inside of the hub instead of cush drive rubber bumpers, and because it had no oil created the noise that worried me.
A normal (which yours may not be) slipper with ball and ramps makes no different noise when lubed or dry, this is why it is important to remember to lube them. Your design may be doing this for you. I have to imagine there are a few non-common seals to keep an eye on.
 

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Discussion Starter #14 (Edited)
The back of the pressure plate is toothed


The noise preceded the ill-advised spraying of the plates by 3 weeks, it neither created more nor less noise and only had 20 miles ridden after being squirted. I mentioned the one time over a year ago that I really slammed down two gears hard and heard a strange sound from the clutch - like a 4x4 in low range when you are going steeply downhill using the transmission to slow your descent. Know what I mean? A heavy whine of many gears straining in protest. I think that sound was this slipper clutch in action as the rear tire did not lose traction when it certainly should have ordinarily with that kind of abuse.

Here are two pictures of the hub before cleaning. As you can see, this is not a cush drive rubber type.






Its not rusted, that crap I sprayed on it turned brown from the heat and made a really sticky mess,...

And here is a picture of that odd nut with the oil passages in it, the spacer behind it has a hollow post that lines up with the hub.




I honestly cannot figure out how this all works to be a slipper clutch, but it behaves like one - so wtf?
 

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In picture #2 is that the oil passage you speak of? That is a roll pin to hold the spacer the lock washer and nut sets in. It aligns with the hole in the spacer.

That appears to be a oem non-slipper clutch to me. Yes the center nut color looks different Is it aluminum? oem is steel.

I have never seen a toothed pressure plate that is a slipper nor a pressure plate that does not have room for the posts to move as the hub opens. I wonder if you will find the cush drive if you separate the hub halves. The rubber cush unit should be inside.

The oil you are seeing is leaking past the pushrod seal if I am seeing it right.
 

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In my fractured opinion, replace the pushrods seals and ignore the sounds if it shifts ok and doesn't slip excessively, or replace it with an actual slipper clutch if that is what you are looking for.
 

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That is a standard clutch hub. The cush rubbers are inside the hub [there are vanes on the steel inner and aluminum outer part] if you take it back apart you can separate the two pieces [with difficulty] and see what I'm talking about. If it was an oil pressure driven slipper how would the oil be delivered? There isn't any pressure feed to the input shaft or any way to regulate pressure application. Seems someone was lied to.
 

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Discussion Starter #18 (Edited)
I agree there seems to be no way to push oil in there enough to do any good. That pin is common? Ok then, ..

That hub does not look at all like it was ever meant to come apart after being pressed in. It doesn't look like the aluminum and steep parts can slip past each other like a cush drive or slipper. It did not look like the one my friend had which came apart fairly easily and looked like it was made to do that. So ordinarily something with rubber would be inside the clutch hub, but there is no room for the posts to move still.

So what makes this the quietest dry clutch ever on a Ducati? Could there be another piece of this puzzle on the other side of the input shaft? I did not take the rest of the side off. It is totally back to normal as far as sound goes now, which is totally silent. What ever I did taking it apart fixed that. Perhaps that noise will come back?
 

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The aluminum part is like a hat over the steel hub, so you won't see any movement at the posts. That spider looking washer that fits under the pinned cup the nut holds on is there to keep the aluminum part from separating and pulling off the steel hub. The two parts can be a bitch to separate sometimes and yes the noise will probably come back in another 8k or so.
 

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So what makes this the quietest dry clutch ever on a Ducati? Could there be another piece of this puzzle on the other side of the input shaft? I did not take the rest of the side off. It is totally back to normal as far as sound goes now, which is totally silent. What ever I did taking it apart fixed that. Perhaps that noise will come back?
Lack of wear and tight tolerances? The jingle-jangle rackety-clacket is the plate fingers bouncing back an forth between the basket fingers. Tighter tolerances get less noise. Construction materials also contribute - steel basket -vs- aluminum, etc.

One of the tricks to quieting a noisy clutch is to offset the friction plates by moving one of the steel plates from front to back in the stack. The overall height and engagement stays the same, but the tab alignment on the plates shifts to a less worn part of the basket/fingers.



PS - I'm having flasbacks to Army running cadences here. "Don't let your dingle-dangle dangle in the dirt. Pick up your dingle dangle and tie it to your shirt."
 
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