On 9/28/2011 8:59 AM, bud-- wrote:
....

How do you get variable land speed and constant PTO RPM?

PTO RPM has nothing to do w/ ground speed--independent drive train
gearing from that to axle drive shaft.

Older tractors (and a very few new/current inexpensive) did generate the
PTO gearing off a transmission gearing such that PTO also free-wheeled
when clutch was in. This is ok for light equipment but definitely not
so much for present large equipment--the inertia there can continue to
power the tractor and lead to real control issues. Modern tractors have
"live" PTO that is fully independent of transmission clutching and is
engaged/disengaged w/ a separate control (generally magnetic-controlled
hand clutch lever altho have seen a few recent w/ just a push-button on
the control panel).

To clarify, on those with both 540 and 1100 RPM the two speeds are
obtained by physically interchanging the tractor external drive shaft in
the same drive hub; the two stub spindles have different spline patterns
on the drive side that match up internally to get the RPM, it is like
two transmission speeds but by actually changing gearing by swapping
spindles, not by an external shift mechanism like transmission. IOW,
one operates at either/or, not selectable "on the fly". Any one piece
of gear is designed for and only uses one or the other drive speed.

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