Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > More clutch wierdness - help.

[Shazaam!]

My guess is that one or both master cylinder reservoir ports are partially or fully plugged and the fluid can't return to the reservoir when the fluid heats up.

So when the fluid expands it pressurizes the system and either leaks past the slave cylinder seal or pushes the pushrod causing slippage. First it pushed past the seal, but because it couldn't get by the NEW seal it moved the slave cylinder and therefore the pushrod. Just a millimeter or two is all it takes.

This would also account for the moving engagement point at the lever.

An alternative explanation is that someone adjusted the MC piston stroke incorrectly and the return port is being covered by the MC piston.

Properly adjusted, there should be a 5-10% dead-band of the full lever movement before there is pull resistance felt at the lever. This freeplay is necessary to prevent covering the port as the piston seal expands normally over time, and to avoid placing the piston seal rest location (where corrosion occurs) right at the return port orifice.

Once adjusted, the manufacturer places a potting compound over the screw adjuster to prevent accidental or incorrect adjustment. Check to see if the potting compound has been removed.

[RickyX]

Shazaam,

Sounds like a feasible theory - I will add it to my list of stuff to check.

Since it has only just started exhibiting the fault and nobody has adjusted any screws/potting compound - how exactly do I check if the ports are blocked?

R

[Shazaam!]

Look for a squirt of fluid in the reservoir during the first 5% of the lever pull (Feed Port)
Push the slave cylinder back in its bore and look for a squirt in the reservoir (Return Port)

[RickyX]

OK will do. What happens if I don't get the correct squirts? Is it possible to clean the ports?

[Shazaam!]

I don't recommend trying to disassemble and clean master cylinders or to use rebuild kits. Leave it to the manufacturer to rebuild them. The skill level demands are too varied ... and the safety issues are not inconsequential.

[RickyX]

Took a look in the reservoir for evidence of squirts - NONE!
Mind you, it's a standard 916SPS with a remote reservoir so would you still see the squirts?
I remember my old Suzuki had a non-remote (brake) reservoir and you could see the squirts as you pulled the brake on and off.

Anyway - dunno what to do now!

[Shazaam!]

Any DSC member have a spare MC he could borrow to eliminate this as his problem?