Clutch Judder
 

I'm sorry if this has been covered before, but i can't find any old threads that help.

I have a slipper cluch fitted to my 996 and on pulling away the clutch judders badly, slipping and griping until the lever is fully released and the clutch is fully engaged.

I have tried changing two plane plates with two more old dished ones to try and help but this doesn't seem to make any differance.

I have been told that they 'all do this sir' but i belive there must be an answer.

Any help would be greatly appreciated.

Have you tried getting all the clutch dust out?

I have a vented cover and did clean it out 100 miles ago to no joy.

I have thought about adding an extra 1.5mm plate to increase the clutch spring pressure, however it will also make the clutch heavier to use.

What make of clutch is it? How many miles has it done?

Its red!

sorry, i bought it from pro twins last year for about £500. Since then I've only done about 1500 miles.

I did have one problem when it was new. if you gave it full throttle on the motorway the revs would jump. As the plates wore in it reduced and eventually disappeared. don't know if it is related though.

The key to proper clutch engagement behavior is having the proper clutch plate stack height, that in turn, establishes the point where you get full engagement - and the proper clutch spring preload.

The higher the stack height, the greater the preload on the springs, and consequently the greater the force pushing the plates together when you release the lever. Since you say that the clutch doesn’t sufficiently engage until the lever is fully released, this tells us that the plate stack is a little low, such that there’s insufficient force to prevent plate slippage (and sometimes judder) until you reach full lever extension.

Like Ducati does for the OEM clutches, the manufacturer of the slipper clutch gives specific instructions on the stacking order, plate type, spring plate positions, spring plate orientation (convex side out) and stack height (38mm.) In doing so, they establish the point where the the slipper clutch begins to slip under a reverse torque condition.

You can change this recommended slip point, however, if you raise or lower the stack height. The shorter the clutch pack, the earlier it slips. Race teams do this all the time to suit a rider’s preference.

However in doing so, you’ll also change the behavior of the clutch during it’s initial engagement. On the track, it’s more important to the rider to have the slipper-function engage at the right time, so the behavior at initial launch becomes a secondary consideration.

On the street however, (and in your case,) the recommended pack height is causing objectionable behavior at launch, so the cure is to use a 0.5mm or-so thicker plain plate to change the “friction zone” on the clutch lever. But, then the slipper will need a higher reverse-torque to actuate.

So when you hear “they all do that,” what they’re telling you is that the slipper has been properly set-up for the track according to the manufacturer’s instructions.

The bottom line here is that slipper clutches are primarily track equipment because of this trade-off between road and track behavior. Some manufacturer’s slippers are better behaved than others in this regard.

how good are you.

thanks, i will try a differant stake height. Am i right in thinking that this will make the lever heavier.

Yes, but not noticably.

Slipperclutches wear a bit more than normal non-slippers. A trick to reduce grabbing and "judder" (at least for sintered discs) is to give the frictionplates a good spray of 5-56 or WD40 and a quick wipedown with a rag.

Slippage under power is propably caused by your friction plates being worn, the pressureplate then sets on the clutch hub. There should be at least 1mm free room between the pressure plate and the hub.

[Edited on 21-2-2004 by Bj.O.rn]

Another possible slant on the problem. I fitted a slipper for a customer last year that he'd bought off E-Bay.
It was a lot worse than the problems you're having in that it repeatedly lost drive. Pick up was terrible and it took a few hours to suss out.
What was happening was the tangs on the friction plates, at the outer most side of the pack, were catching on the spring steel ring that goes around the circumference of the basket.
When cold, the fit was "snug" but they cleared it and the clutch worked. Once the smallest amount of heat was in the clutch, the plates started rubbing. The other symptom was the clutch lever went all spongy, through there be reduce spring presure from the clutch.
The pack thickness is important, as Shaazam suggests, but if the friction plates are rubbing just a little bit, but the spring pressure is still strong enough to engage the clutch, you won't really notice anything worse than the grinding you're experiencing.
Worth a close check of the basket and outer edges of the tangs for scuffing marks or even light polishing.
A new Surflex clutch pack solved the problem in this case but if your plates are in good condition, maybe a light dressing of the tang edges could solve it.