Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > SLIPPER CLUTCH PROBLEMS

[LOOMIE]

FOLKS
I RECENTLY BOUGHT A SLIPPER CLUTCH FROM CASOLI. SINCE FITTED HAVE BEEN HAVING PROBLEMS WHERE AFTER A WHILE (60-70 MILES) I LOSE DRIVE.
THE THING WAS FITTED AS PER CRAPPY DRAWING SUPPLIED (BUT NO INSTRUCTION). ALL WENT TOGETHER OK AND OFF I WENT. CHANGING GEAR AND THEN NOTHING , COASTED TO HALT. BACK HOME SPLIT PACK AND NO GLAZING/CONTAMINATION. STRIPPED AND BACK TOGETHER , SAME AGAIN ABOUT 60 MILES (2 DAYS COMMUTING).
LEVER/CYLINDER SEEMS TO BE OPERATING CORRECTLY. CORRECT NO AND ORIENTATION OF PLATES. SEEMS THAT THE PRESSURE PLATE IS NOT COMING ALL THE WAY BACK IN WHEN LEVER IS RELEASED, (NEW SPRINGS)YOU CAN STILL WIGGLE THE SLACK FRICTION PLATE LUGS.
THE CLUTCH DRUM CENTRE NUT IS TIGHT BUT SEEMS TO BE HOLDING IT HARD AGAINST COLLAR/BEARING BELOW, WILL THIS STILL ALLOW IT TO RISE ON THE RAMPS/BALLS?

ANY IDEAS GUYS??

cHEERS
sTU.

[JPM]

Sounds to me like the pressure plate isn't applying sufficient pressure, but why it would be OK for 60-70 miles is beyond me. The clutch stack height is pretty critical, are you sure you have enough plates etc there.

I had a similar thing that I had left 1 plate out, maybe 2, and was OK for a good few hundred miles, but as soon as the plates started to wear slightly there just wasn't enough depth in the clutch pack to stop spinning under such load, and I ground to a halt I needed to add plates for it to work correctly.

Maybe the pressure plate doesn't fit flush with the plates? maybe the bearing in the pressure plate isn't a flush fit.

I assume you cannot move the clutch hub when there are no plates in there? and that the spring washer etc is nice and tight???

[breakout]

Too few plates and the friction side of the pressure plate contacts the clutch driven drum , and no amount of spring pressure will bind the drum; clutch will slip and burnout.
Too many plates and on clutch lift the pressure plate splines ( if the clutch has them) may disengage the drum, and depending on the clutch the lift balls may come out off the ramps and jam the floating hub; thus stopping the pressure plate from loading the plates and locking the clutch; result clutch slip.
Slipper clutches are all about thhe amount of gap in an assembled clutch between the pressure plate and the clutch inner drum end surface (axail gap) I think yoyodyne sell clutch shims, (various thickness driven plates) to allow the fine tuning of the clutch operation.Pull the back wheel backwards to lock the clutch then measure the distance from the out side of the pressure plate to the end of the floating drum record (freqently possible through holes in the outer pressure plate that line up with the end of the drum)measurement,then remove 4x plate sets reassemble clutch, snap wheel backwards and measure , record , this last reading is the minimum pack thickness that will allow the springs to lock the clutch . subtract the two measurements and the arrived at distance is the total amount of wear (thickness) the plate pack can sustain before clutch slip.adjust total plate pack thickness untill you like the way it works; clutches also come with different ramp angles which change the unlocking characteristics , as does the star spring,I like the clutches to transmit a fair amount of back -torque to ensure recovery from high-speed high angle wheelies when the air stream starts providing unanticipated lift ,and the back torque is what gently brings the bike down, if i muff the rear brake

[breakout]

thanks to Sigma
So how does a Sigma slipper clutch work?

Diagram A
The following drawings (have another look at the pictures above for the detail of the internal ramps as well) show the basic idea; I would also suggest a nice cold towel for the head at this point.

When the engine power is driving the bike forwards in the normal direction the little ramps lock solid; the clutch acts completely normally. Diagram A shows the normal situation.

Under a slowing situation Diagram b shows what occurs when the engine is being turned over by the rear wheel; as gearshaft B is turned over by the rear wheel the clutch (attached to gearshaft turned over by the rear wheel the clutch (attached to gearshaft a) is forced to take the load in the opposite direction, this forces the centre of the clutch up the 45-degree ramps; so starting to force the clutch pack apart.

Diagram B

As soon as the clutch pack stops gripping (i.e. when the centre has risen slightly on its ramps) most of the force to hold the pack apart is lost and theoretically clutch grip is re-established as the pack tries to come back together. In practice the clutch establishes an equilibrium position where there is just enough force being transmitted to hold the clutch apart (i.e. to hold the centre partially up the ramps) yet just enough to stop the engine being revved up, this equilibrium point can be adjusted either by varying the spring rate or the effective preload on the springs holding the clutch together or by varying the height of the assembled clutch pack. This is why you will often see theoretically rich well-funded race teams sorting through endless piles of seemingly knackered clutch plates trying to get precise pack thicknesses they want to give their rider the feel he is used to.

Copyright Neil Spalding 2002- 2005


So how does a Sigma slipper clutch work?

Diagram A
The following drawings (have another look at the pictures above for the detail of the internal ramps as well) show the basic idea; I would also suggest a nice cold towel for the head at this point.

When the engine power is driving the bike forwards in the normal direction the little ramps lock solid; the clutch acts completely normally. Diagram A shows the normal situation.

Under a slowing situation Diagram b shows what occurs when the engine is being turned over by the rear wheel; as gearshaft B is turned over by the rear wheel the clutch (attached to gearshaft turned over by the rear wheel the clutch (attached to gearshaft a) is forced to take the load in the opposite direction, this forces the centre of the clutch up the 45-degree ramps; so starting to force the clutch pack apart.

Diagram B

As soon as the clutch pack stops gripping (i.e. when the centre has risen slightly on its ramps) most of the force to hold the pack apart is lost and theoretically clutch grip is re-established as the pack tries to come back together. In practice the clutch establishes an equilibrium position where there is just enough force being transmitted to hold the clutch apart (i.e. to hold the centre partially up the ramps) yet just enough to stop the engine being revved up, this equilibrium point can be adjusted either by varying the spring rate or the effective preload on the springs holding the clutch together or by varying the height of the assembled clutch pack. This is why you will often see theoretically rich well-funded race teams sorting through endless piles of seemingly knackered clutch plates trying to get precise pack thicknesses they want to give their rider the feel he is used to.

Copyright Neil Spalding 2002- 2005


So how does a Sigma slipper clutch work?

Diagram A
The following drawings (have another look at the pictures above for the detail of the internal ramps as well) show the basic idea; I would also suggest a nice cold towel for the head at this point.

When the engine power is driving the bike forwards in the normal direction the little ramps lock solid; the clutch acts completely normally. Diagram A shows the normal situation.

Under a slowing situation Diagram b shows what occurs when the engine is being turned over by the rear wheel; as gearshaft B is turned over by the rear wheel the clutch (attached to gearshaft turned over by the rear wheel the clutch (attached to gearshaft a) is forced to take the load in the opposite direction, this forces the centre of the clutch up the 45-degree ramps; so starting to force the clutch pack apart.

Diagram B

As soon as the clutch pack stops gripping (i.e. when the centre has risen slightly on its ramps) most of the force to hold the pack apart is lost and theoretically clutch grip is re-established as the pack tries to come back together. In practice the clutch establishes an equilibrium position where there is just enough force being transmitted to hold the clutch apart (i.e. to hold the centre partially up the ramps) yet just enough to stop the engine being revved up, this equilibrium point can be adjusted either by varying the spring rate or the effective preload on the springs holding the clutch together or by varying the height of the assembled clutch pack. This is why you will often see theoretically rich well-funded race teams sorting through endless piles of seemingly knackered clutch plates trying to get precise pack thicknesses they want to give their rider the feel he is used to.

Copyright Neil Spalding 2002- 2005


So how does a Sigma slipper clutch work?

Diagram A
The following drawings (have another look at the pictures above for the detail of the internal ramps as well) show the basic idea; I would also suggest a nice cold towel for the head at this point.

When the engine power is driving the bike forwards in the normal direction the little ramps lock solid; the clutch acts completely normally. Diagram A shows the normal situation.

Under a slowing situation Diagram b shows what occurs when the engine is being turned over by the rear wheel; as gearshaft B is turned over by the rear wheel the clutch (attached to gearshaft turned over by the rear wheel the clutch (attached to gearshaft a) is forced to take the load in the opposite direction, this forces the centre of the clutch up the 45-degree ramps; so starting to force the clutch pack apart.

Diagram B

As soon as the clutch pack stops gripping (i.e. when the centre has risen slightly on its ramps) most of the force to hold the pack apart is lost and theoretically clutch grip is re-established as the pack tries to come back together. In practice the clutch establishes an equilibrium position where there is just enough force being transmitted to hold the clutch apart (i.e. to hold the centre partially up the ramps) yet just enough to stop the engine being revved up, this equilibrium point can be adjusted either by varying the spring rate or the effective preload on the springs holding the clutch together or by varying the height of the assembled clutch pack. This is why you will often see theoretically rich well-funded race teams sorting through endless piles of seemingly knackered clutch plates trying to get precise pack thicknesses they want to give their rider the feel he is used to.

Copyright Neil Spalding 2002- 2005


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