Shazaam's Tech Library - Difficulty engaging neutral

A useful technical article from guest contributor Larry Kelly of San Diego CA (aka Shazaam!).

Difficulty in selecting neutral is the result of the clutch plates still dragging after the cluch lever is pulled in. As the plate friction material wears, the plate stack height gets reduced so the problem usually becomes less severe over time. If you've replaced the clutch plates, the stack height may be too high, which will also cause the problem.

Two possible solutions:

Your 4-position clutch lever adjuster is placing the lever too close to the handlebar so you're not getting complete separation of the plates. Try a different adjuster position that gives a longer lever stroke.

If you are still unable to engage neutral, the most likely cause is air in the clutch hydraulic line. A trapped air bubble can compress (the fluid can't) so you won’t get a full stroke of the clutch pushrod and the clutch doesn’t fully disengage. The engine temperature at the slave cylinder location can easily reach 212 degrees F (the boiling point of water), and nearby small pockets of water, as they boil, introduce water vapor in the line that causes behavior just like air in the line does.

The amount of water that hydraulic fluid can hold in solution is dependant on the temperature of the fluid. So, The Ducati clutch hydraulic circuit is like a little water generator. When the fluid heats-up from engine heat, it can hold more than five times more water than it could hold at room temperature. Moisture usually enters through leaks in the reservoir cover and gets absorbed into the fluid.

Then the fluid cools down when you shutdown so the additional fluid that could be held at the higher temperature, condenses out into water droplets that sink to the low point of the system - to the slave cylinder. This happens over-and-over until enough water has accumulated at the hottest point in the system. At 212 degrees F it boils and your clutch actuation goes south.

So, flush your system to get rid of the water completely.

Another common reason that the clutch won't completely disengage is that the aftermarket force-reduction slave units (and later model Ducati slave units) move the clutch pushrod less distance - a design trade-off to accomplish a reduction in clutch lever forces.

 

Tip " 749/999 - its a pretty common fault on the 749/999's to have regular clutch bleeding sessions.Take a look at the fluid levels in the master cylinder while the bike is on the sidestand,...not much in there,...is there??Dunno if air gets in here,just that some need a bleed now and again,some dont.
Dead easy to do on these bikes,just remove the master cylinder cap.Have a look inside,...see that little bolt head?He's your boy,(cant remember the exact size,4mm?)undo the bolt a little and gently squeeze/pump the clutch lever.See those bubbles coming out,....continue squeezing untill they disapear.Tighten the bolt,replace the cap,...hey,you have just bled your clutch.Sit back in the warm glow of a job well done.
NB,its good to have plenty of rags lying around to catch any fluid that might want to spoil your paintwork.Its also best if the bike is upright,like on a paddock stand or summat.

 

info taken from this thread from DSC forums

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