Ford 2002 F650 Owner's Manual page 140

Driving
engaged by clashing the gear teeth. This may damage the PTO unit and
the transmission PTO drive gear teeth. This could result in further
damage to the transmission and PTO.
PTO operation with vehicle stationary
To operate the power take-off, stop the vehicle, idle the engine and set
the parking brake. Make sure the gear selector is in any forward drive
range, then engage the PTO. After the PTO is engaged for stationary
vehicle operation, move the range selector to N (Neutral). Increase the
engine speed until the desired power take-off operation speed is
obtained. To disengage the PTO after operation with the vehicle
standing, release the throttle, allow the drive equipment to come to a
stop, and then disengage the PTO.
When the PTO is operated with the vehicle stationary, the
transmission must be placed in N (Neutral). If the transmission
is not in N (Neutral) and is equipped with a remote throttle control, an
increase in engine speed can overpower the parking brake and cause
the vehicle to move, possibly resulting in personal and/or property
damage.
PTO operation while vehicle is moving
After the PTO is engaged for driven vehicle operation, shift to the
desired range and drive the vehicle. The speed of the PTO, during this
period of operation, will always maintain direct relation to vehicle speed.
PTO speed will decrease in relation to vehicle (transmission output)
speed as shifts to a higher gear occur. When operating the PTO while the
vehicle is moving, the PTO may be disengaged whenever it is no longer
required. When there is no load on the PTO gear, it can be pulled out of
engagement.
Power take-off (PTO) operation with an Allison automatic
transmission (MD applications)
The PTO drive gear is engine driven and provides direct engine power.
The PTO can be operated when the vehicle is either stationary or
moving.
The PTO gear is in constant mesh with the drive gear in the torque
converter housing. A friction clutch or constant drive is used to transmit
power to the PTO.
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