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Discussion Starter · #1 ·
I know my AN400 has a dry (and rackety) clutch 馃檪
But how do clutch plates grip if they're oil soaked? Not intuitive.
[I've had a Shadow 1100, Concours, and now Sportster all with wet clutches.]
 

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Its like the same as inside most Auto/Truck automatic transmissions.
 

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My BMW R1100RT has a dry clutch. Don't have to worry about using "energy conserving" oils.
 
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But how do clutch plates grip if they're oil soaked? Not intuitive.
Short answer:
The friction material is rough and porous so spring pressure pushes the oil out of the way through the gaps and channels - allowing the 鈥渢eeth鈥 of the friction material to grip.


long answer:
Interesting question. It is to do with asperity and the different forms of lubrication (boundary, mixed and hydrodynamic)
Sliding surface grip depends on asperity, the tiny peaks on a 鈥渟mooth鈥 surface.
On a steel bearing surface, asperities are very small; enough to hang on to oil molecules but small enough for oil molecules to flood them eliminating the hills and valleys producing a nice smooth film to ride on (tribological film).

Friction material has large asperities, too big for oil molecules to fill/bridge during low speed contact.

Speed is important - what鈥檚 called the Stribeck curve.
So on initial contact the surfaces are travelling at high speed relative to each other and this maintains a film. Not much torque is transmitted as it鈥檚 just oil film on oil film (hydrodynamic).
With more pressure oil gets displaced through the hills and valleys and asperities begin to contact, but there are reservoirs of oil molecules in the valleys to re-coat them - this is the 鈥渕ixed鈥 regime.

The two surfaces start to become matched in speed and some torque is transferred. As relative speed reduces and/or pressure increases the oil has an easy way out on a rough clutch that it doesn鈥檛 have with smooth bearings - so the clutch asperities clear and break through the film far earlier and you get direct dry contact on interlocking hills and valleys of the plates.

You still get reduced wear and debris cleaning, the other functions of lubrication.
 

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2022 Matte Deep Blue Kymco AK 550
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And just to add to this. All fluids have SOME element of friction. Even air has friction. The faster you move through the air or any fluid the more friction becomes noticed. When fast airplanes go as fast as they can through the air their "skin" gets hot... due to the friction. The trick with a wet clutch is that you don't want the oil to be TOO slippery. Thus the warnings about Resource or Energy Conserving oils that have even more additives (almost all oils have some additives) that make them more slippery than the clutch can handle to work properly and also tend to coat the clutch plates and cause them to become possibly permanently unusable for their intended purpose. Simplified terminology.
 

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Then conversely, you have the clutches in limited slip鈥檖osi鈥 differentials, that grab too much and produce destructive chatter, unless you add additional friction modified additives to the gear lube. 馃槈
 

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A clutch is designed for the environment it is intended to be used in. Wet clutch for being immersed in oil and dry clutch for, well, remaining dry. ETC. So really there are none that will grab too much unless they are being used in a way not intended.
 

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Discussion Starter · #10 ·
Wow this is interesting. Worth a couple more hours on the interweb 馃檪
 
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