Axle Conversions; Two-Speed Rear Axle (If Equipped) - Ford F650 Owner's Manual

Driving
are not slipping. The differential must not be locked when the vehicle is
traveling down steep grades and traction is minimal.
Note: Never use the differential lock at vehicle speeds above 25 mph (40
km/h).
Note: The driver-controlled differential lock function will vary with some
transmissions.
• Vehicles equipped with an Allison 3000 Series transmission: The
differential lock and differential lock light will automatically disengage
at speeds above 25 mph (40 km/h). The differential lock will remain
off until either the vehicle is restarted or the differential lock switch is
turned off then back on.
• Vehicles equipped with a 5–speed, 6–speed or 7–speed manual
transmission or a non-MD automatic transmission: The driver
must manually deactivate the differential lock if using it at speeds
above 25 mph (40 km/h).
• Vehicles equipped with a 10–speed transmission: The differential
lock can only be activated when in low range and it will only stay
activated until it is turned off or when the transmission is put into
high range. When active and shifted into high range, it will temporarily
deactivate (automatically) until low range is selected again.

Axle conversions

It is not recommended, or approved, for axle conversions to be
performed. However, it is understood that, on occasion, aftermarket
add-on axles are installed by others on the truck chassis which allow
operator control for weight transfer from other axles (i.e., air lift axles).
When operating a loaded vehicle, the driver must keep all
adjustable axles on the ground at all times, supporting their
share of the vehicle's load. Failure to do so can overload other axles,
tires, wheels, springs, steering components, brakes and frames,
resulting in early component failure, loss of vehicle control, possible
property damage and personal injury.

TWO-SPEED REAR AXLE (IF EQUIPPED)

A two-speed rear axle allows the driver to select a LO range for greater
pulling power and a HI range for greater road speed and fuel economy.
These ranges can also be used to provide additional steps between
transmission shifts when driving on steep grades and/or fuel economy
may be factors.
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