Author Topic: Slipper Clutches - The Why's and Wheretofor's, Etc, etc, EtCeTeRa!  (Read 16338 times)

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Offline Brett

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This is a good write up Vince.  Well done.

As you know, I have a Ducati Performance slipper in the 1098, and I couldn't be happier with it, mostly for all of the reasons you mention.  It takes the nervousness out of back shifting, and that fear of rear wheel chatter getting the better of you, culminating with you standing at the Fraser's spares counter saying 'how much did you say that fairing was ?'...

For me, it made the thing a whole different bike to ride and ( touch wood ) a whole lot more fun.  I also looked at options to purchase locally and via Ducati, but in the end the costs were prohibitive.  I eventually landed mine here from the US, for just under AU$900.00, which was almost half local pricing.

With your exposed clutch, do you think that the weather and road grime / debris plays any part in this wear problem ?  Your comment about the old clutch assembly getting roughly twice the life of the slipper, takes me to materials.  I haven't done the math, but I reckon my original clutch basket etc was considerably weightier and my guess is that the difference is industrial grade 'standard' components, versus the 'race once and then bin' material of the ( most ) slippers.

I'd be intrigued to hear about wear patterns in the wet slippers in 848's, and ( God forgive me ) some of the Jap sports bikes.  My guess is that lube and heat differences would make a difference.

But then you're the Engineer...
Mvlti svnt vocati, pavci vero electi

Offline VinceS

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The Short Story:
I have had a 48 tooth STM Evoluzione slipper clutch fitted for a while now, but after nearly 30,000km found the basket is badly worn. This has lead me down a long path over Christmas to figure out what the smartest way to deal with it is. The short story is that I have ordered an APTC (Adler Power Torque Clutch) OEM dry clutch replacement kit to fit with the original basket. However I have collected a lot of info in the process and figured I should share it.

It is coming from here:
This is an APTC OEM dry clutch basket retrofit $US1,422 for 2002+ (alloy) or $US1,377 for 2001- (steel) plus shipping $US62.25. So for the alloy one in my hands is a smidge under $1,700.

I can't find any reliable info re problems reported with their life / operational issues, so I am concluding no news is good news! Anyway they have had 5 years now to iron out any bugs. I will hassle STM for a replacement basket at a good cost and put the Evo towards the race bike project for next year when presumably Ringwood will have come on line.

Why Would You Want a Slipper Clutch Anyway? What Are The Issues?:
 Just for anyone contemplating getting a slipper clutch and using this thread for guidance there are three really big "need-to-know" issues beyond the obvious price / logistics of the exercise:

1) It is a brilliant safety device which you will use often if you like to "get into it a bit". The rear of the bike just follows you tidily into a corner and all that hopping, waggling, stepping out and other similar misbehaviour you used to somehow adapt to simply vanishes. It is one thing to have the bike getting a bit squirmy hauling out of a corner, it is an entirely different thing being squirmy on the way in, you don't want that at all!

2) Increased basket wear rates due to the lack of a damper on the inner hub. There is fairly good evidence around to say friction plate wear is barely if at all affected by the slipper action, at least in a street application. Certainly I only used about 20% of the total clutch friction plate adjustment available in the time it took to shag a basket, and this is a commonplace experience. I am expecting the APTC clutch to greatly improve on the package life anyway, we?ll see what we get?..

3) Don't think you are going to be able to clutch start your bike in a hurry!

For my money the first one far outweighs the latter two. Sure I could have a good old whinge about the various cost issues, but I would rather pay than lose the feature.... When you get a brain fade from so enjoying rolling on hard out of the last corner you forget to process that you are running into the next one with around 70km/hr more than what would be regarded as "a bit hot", stand the sucker up and all anchors aweigh, only to find the rear end hanging out at 45 degrees or something ridiculous you will wish you had paid the price before learning the lesson!

Then, your reward for NOT backing off then and going for a compulsory high side is to get the thing back on track by a bit of neat feathering and other reactions, not able to be put into words but being there when needed - and hauling through the particular bend in the road with a blast of adrenalin to help you cope. Followed by riding meekly along slapping yourself on the wrist for a while before (hopefully not) doing it all again. But not everybody wants to travel here. Or they learn to gently tug on the clutch lever and do a bit of manual slippering, which can be a bit tricky in the heat of the moment! No, backing off is NOT AN OPTION, the psychology / physiology of which is an entirely different (and much longer!) discussion. Summarised by ?Know Yourself and be happy?.

This is why we NEED slipper clutches to work. The other part of getting this equation right is a properly set up Power Commander 3 to let you keep out of 2nd gear more (and avoid the issue almost completely, until the next time anyway!). Oh, and a truckload of patience to slowly push the comfort zone out to the point where this description is not the lunacy it will appear to most, but a completely credible example of using the tools (to just) within their design limitations!

What Was That Clutch Starting Issue Again?:
Interestingly nobody talks about this last point and, as a proud owner of a new slipper, it is handy to know you can't clutch start the bike like before. Before you need to try it and have an "oh f" moment getting going in a hurry, after you ran the battery down that is. It isn't in the instructions and I found out the hard way but luckily there was a car with jumper leads around.

So, if you put a slipper on do those other electrical fixes to get really solid wiring from the alternator - rectifier - battery - starter motor willya? And don?t leave the ignition on and walk away! You can clutch start with a slipper in my experience, but you need to be going around 60km/hr before it will get enough bite to kick the engine over. Probably can do it from less if you have enough juice to use the starter to kick it in while the bike is sliding on the slipper. Dunno, I haven't experimented too much, but it is easy just to shut the engine down while riding along then try and start it with the rear wheel, you soon get an appreciation of what is realistic!

Why / What Is an Adler APTC Clutch?:
The Adler clutch is the new OEM slipper put in Ducatis, called the APTC (Adler Power Torque Clutch). The APTC clutch has been fitted to many new Ducati models for the last 5 years, as a wet clutch. It uses a spiral centre that causes a greater amount of torque to be applied as you apply power. The upshot is that the springs can be lighter and the lever pull less. In reverse this feature acts as a slipper function. Neat huh? Adler now make it available as a retrofit to suit dry clutch Ducatis. Worth a go I figured.

I went looking to find out exactly who Adler are and why they should be able to make a good slipper clutch, (assuming that might be the case).
This is Adige, who are ?the after market division of ADLER S.p.A., one of the world leaders in motorcycle component innovation, design and production?:
This is Adler, but the Adige stuff is better:

APTC clutch assembly video shows how these things are made:

Normally the Adler products would be distributed via but it has been broken since at least Christmas, hence I have found an alternate source per above.

See here for the long story on the APTC: (Press F5 to get rid of the advert).

The Alternatives:
In coming to the above conclusion I must say there is some other very tempting options, for your reference this is some more stuff I found:

Over the counter at Newcastle Frasers, Darren Lewis showed me a pretty smick looking Ducati Performance slipper clutch. My first impression was that it had a better inner hub configuration than the STM unit. It cost about the same as the STM did 3 years ago, and is very much a viable back-up plan if the APTC doesn?t come through in time for Turismo. (FBF slipper $US1,200) $US1,388 (ducati-corse-wsbk-style-spring-slipper-clutch) (TSS info)

Mb2C products come from here? this explains the options (turn Google auto translate on):

STM: (rebadged TSS?)

Tips from Matt: I?m now using 12T basket as the jangling noise of the 48T kit drove me mad. I think STM go for best performance so use sintered steel plates and alloy basket. They could use steel basket but i guess this adds a lot of weight for no gain other than longer life.

I have the same set up in my STM slipper clutch 12T ie alloy basket but the best ducati plates ie bronze sintered steel racing plates. These provide better feel and performance but at a cost to basket life. I?ve tried alloy plates etc but I didn?t like ?em after using bronze steel sintered racing jobbies.

I think slipper clutches last about 2/3 the rate of standard set up and less with hard use.

For alternate clutch packs try Mb2C as they do alloy 48T plates and basket kits for all ducati clutches and slipper clutches. They have three different spec alloy plates depending on what you want to spend.

Good Non-Slipper Options?: Looks like the best non-slipper around. See manuf (less info than proitalia)

Check the above listed sites also, they all have good looking non-slipper options around. However, as part of this exercise I have been in touch with Wiseco who make the best non-slipper clutches bar none, for dirt bikes! They hadn?t realised what potential there was in the Ducati arena but now do ? and are very interested in checking it out. They may also do slippers, I am working on them for that still. Why am I so excited about this option? The reason we are really interested is: "Wiseco forged clutch parts for the off road market wear so well that we offer a lifetime guarantee."

It's early days, but the initial Wiseco market mgr responses have showed genuine interest. However this is not a market segment they have looked at before as they have primarily tackled the off-road market. Their initial thoughts are that the bits we want are close to what they already have forgings for, therefore getting a few sample clutches out there might be a useful way to test the market. I have suggested they have a chat to LT Snyder in the first instance, we'll see where it goes from there.

My honest belief is the ducati clutch world market could easily run to 10,000 units annually. Does anyone have a credible way to get a quantitative assessment of what the market could be? Both for standard clutches and slippers?

Fitting Issues?:
Will cover this in a later post, maybe. However just to mention I have seen a fair bit around about the difficulties of undoing / torquing the retaining nut and / or basket bolts up. I had no drama putting the bike in 5th (not 6th - strength issues) and standing on the back brake with medium pressure. I expected to have to kill off a couple of old steels to make a hub holder, but never did as this worked. But don?t, whatever you do, go sticking a bar on the spring posts as they will snap off. You can recess a high tensile bolt in from the back and tap / screw the broken pin back on but it is an unnecessary waste of time compared to not making the mistake in the first place. How would I know? Don?t ask, suffice to say there is a Monster in the house with a standard clutch??!

My Problem:
Don?t get me wrong, the STM Evoluzione 48T slipper is a GOOD CLUTCH. At $2,492.15 incl slave cyl 3 years ago it would wanna be! The pull on the lever is reduced by both the use of the STM slave cylinder and the use of a diaphragm spring clutch. Expensive sure, but pay back is in increased riding safety and reduced aching hand after a long day. However the increased noise of the 48T is a bit of an issue and you can?t do the mod to quiet them down like you can a standard clutch. It is a more whispery kind of jangle, but still loud, out of the box! I guess that is because there are so many extra surfaces hitting together. I have wrestled with the idea of doing a silencing mod but not come up with one that will work. The double up of friction plates in the bottom of an OEM (to ?connect? the hub and basket and shut it up when in neutral / riding in gear) really can?t be done with a slipper as they would need ridiculously close tolerances to get the benefit but allow the slipper to work, plus there would be a possibility of jamming occurring ? all too hard.

There is also the dual benefit of having the lighter basket and the DP lightened flywheel in the "taking off like a scalded cat" sensation, it is as big an improvement as adding 3 teeth on the rear sprocket. No downside I've found. A side benefit is that the bike flicks more quickly through tight esses, which was a pleasant and unexpected bonus! However, mostly, the benefit here is from the flywheel not the basket. The lighter S wheels are also important.

So, just when I thought I had "done the job properly", along comes the discovery that getting 30,000km out of a basket is considered "really good" - now that I talk to the local mechanics at Frasers and NFI technical personnel! This is not real flash when that is only 18 months or so of actual riding (after time out to build a house) ? club days, Turismo and the like ? no commuting. Considering I had more than double that life out of the stock clutch assembly - which I have just put the plates from it in the Monster to "finish them off" - I figure that is pretty abysmal. I don't ride any differently with the slipper than before, just that now the frequency of those ring clenchers from going in a bit hot have dropped right off. This is in general touring mode, regularly interspersed with ?a few fast twisties".

The STM clutch is pretty good from a basic operational perspective, and appears to be well made. The real problem for me is that this relatively short in-service life was a total surprise. I thought I had bought the best, certainly was told the 48T would give reliable long life and of course Warren Lee also took time out to wax lyrical about the virtues of an Evoluzione clutch on quite a few occasions! I was well aware of the issues of Ducati clutches and resigned to accept something just short of 100,000km for a well treated unit (which mine is) from the standard clutch but it never occurred to me that buying the premium product would result in a much shorter life. I certainly wasn?t told about this. The basket is worn out after 29,500km of touring travelling only. The remainder of the components are close to ?as new? condition, which leads me to believe the alloy basket material is faulty, or at least a grade has been used that is not fit for the chosen service. Particularly since the alloy inner hub is virtually unmarked.

 The attached pics show the problem, plus the good bits. For now I have fitted a 2.5mm spacer under the hub which moves the friction plates to the bumps and allows the clutch pack to disengage properly, although a little fluffy in operation (variable feel as plates catch on the edges slightly). My clutch stack height was at 35.85mm which is hardly any wear at all, I bumped it back to 36.35mm on reassembly. I do note that the friction plates are steel and the basket is alloy which I read elsewhere here is a no-no. However this is how it came from STM and I would point out the inner hub is also alloy yet it is virtually unmarked. Plus the sintered steel friction plates have a nice feel about them in use.

In terms of gathering the knowledge, this is an extract of what the local importer technical rep had to say:

"The wear in the clutch basket is caused by clutch pack hammer,this is caused by a combination of ,on /off throttle (normal) and the fact that the engine has an odd (as opposed to even ) 270 degree firing interval.These factors are more prelevant at low engine speeds such as commuting/city traffic.

Unfortunately when the clutch becomes a slipper style there is also an added wear factor because of the two piece clutch hub and the fact that cush damper in the std hub doesn?t exist in the slipper type.

These things all add up to backlash in the clutch assembly which causes the hammer and because the clutch plates are clamped up on the hub (or outer hub with the slipper type) the pack hammers the basket.

For example if you compare a 748 (normal clutch) and 748R (slipper) the R will knock its basket out in half the time compared to a std clutch under the same type of use.

The slipper clutch is designed as you know for racing and as such the performance level for racing outweighs the higher wear rate of the associated components.

I would suggest the wear in the basket is normal for this type of clutch."

The gentleman who said this is a totally reliable, matter-of-fact no bs type of fellow. I would emphasize one of the key things he has mentioned, that is that the Evoluzione slipper clutch deletes the rubber damper in the inner hub. If, like me for a long time, you thought the inner hubs were solid they are for sliipers (all?), but the standard inner hub presses apart and there are a bunch of rubber damping elements in them. This is bound to make the problem of basket wear worse, but it doesn't explain why the inner hub is not equally afflicted (remember that Isaac Newton equal and opposite reaction stuff!).

I would be quite happy to go to a wet clutch if that was going to get reliability and life. However this is not a foregone conclusion. When I say "quite happy" I would miss the look of the thing!

So, this is the process that has lead me to buy an APTC clutch for my Ducati. Obviously a way more important thing to be doing over Christmas than mowing the lawn. Now, the lawn can get mowed while we wait for the arrival of this shiny new bit of kit......!
« Last Edit: 19 Dec 2015, 03:05 PM by VinceS »
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