The friction disc drive was patented in 1904 by John Lambert. Here is a quote from the John-meister himself:
"In practice I have found that this combination of aluminum and fiber bearing surfaces gives the maximum
degree of friction and durability, thereby especially adapting the gearing for use on motor vehicles of the
heavier kind, where the friction surfaces are at times subjected to great strains, and must, therefore, have
a frictional contact of a high degree of efficiency in order to avoid slipping. It will be observed that the
aluminum is advantageous also, because it will not tarnish or rust appreciably, but will always present a
smooth, clean surface to the fiber periphery, so that wear will be reduced to a minimum."
and John oughta know -- his Lambert touring cars were quite sucessful. Here's one with the friction disc exposed:
Now if John says they must have a high degree of frictional contact, I believe him.
So shifting while the disc is firmly in contact would cause excessive wear to the components.
Toro would agree -- they say not to do it in my manual.
Here's a snowblower friction disc:
It seems obvious from the size of the spring holding the rubber wheel to the plate that moving it without releasing
it is going to cause wear. After all it's tight enough to carry a load of 9, 10, 11 or more foot-lbs of torque.
Anyway that Lambert friction wheel would be an awesome mod for high speed travel over to the neighbor's driveway!
