Hi! I am creating this thread to ask what is the physical phenomena that drive the smooth disengagement of clutch discs from flywheels. I am thinking about car clutches, specifically a longitudinal front engine, rear wheel drive clutch type. I've been reading some books that describe the components of the clutch system, their operation, the proper procedure for maintenance and repair, but I haven't been successful in finding a book that describes why the clutch disc disengages the flywheel (the physical and perhaps mathematical models of the operation). I understand how it engages and why it stays engaged, but after the pressure plate stops exerting pressure, why does the clutch disc backs away from the flywheel? I've read about the cushion (marcel) springs and about the grooves in the face of friction facings and, well, even though I can somehow get an intuitive feeling that it might help disengage the clutch disc from the flywheel in a straight road (with no slope), I can't understand how a clutch disc is able to disengage when the car is on a downhill road (going down), where gravity will try to pull the clutch disc towards the flywheel. My thought process so far has been like this: well I know that every real surface has some roughness that translates to microscopical (sometimes even macro!) peaks and valleys on said surface. When the pressure is removed from the clutch disc it "just contacts" the flywheel and both can slip past each other. This slip will allow the peaks of the flywheel to exert some force on the peaks of the clutch disc, and this force will cause the clutch disc to gain a (very) small acceleration, which will make it back away from the flywheel. Of course the friction in the clutch disc splines and the gearbox input shaft will bring the clutch disc to a halt after the clutch disc is like 2 ou 3 mm (completely random numbers due to my ignorance of the real ones) away from the flywheel. When the car is on a straight road the clutch disc will not try to move towards the flywheel until the pressure plate forces it. When the car is on a downhill road the clutch disc will move towards the flywheel, but the peaks/peaks interference process will occur once again, and since it would require a lot more energy to rotate the clutch disc and the gears in the gearbox, the system will try, as per the minimum energy principle, to achieve a configuration that minimizes the energy and that configuration will most likely be the separation of the clutch disc from the flywheel. My questions are: is this thought process anyhow conceivable? Does anyone know if there are good references/papers on the subject? I am not doing research work on the subject, nor am I trying to model the system, and this is not college homework. This is just some curiosity of mine that I would really like to satisfy.