Ford F-650 2008 User Manual page 125

Some Dana/Spicer drive axles have a driver-controlled differential lock.
The differential lock can lock or unlock the differential when the vehicle
is moving or stopped. When extra traction is required, the differential
lock will provide full power to both axles.
When the differential is locked, the vehicle's turning radius will increase
(vehicle will "under-steer")
The differential can be locked or unlocked when the vehicle is moving at
a constant speed of less than 25 mph (40 km/h) and while the wheels
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:
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.
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.
2008 F-650/750 (f67)
Supplement
Driving
125