Ford F750 Owner's Manual page 130

Driving
Shifting the axle from LO to HI range - vehicle moving
Accelerate to approximately 56 km/h (35 mph), press the lower part of
the switch while the transmission is in N (Neutral), then release and
apply the accelerator.
Shifting the axle from HI to LO range - vehicle stopped
Place the transmission in N (Neutral), then press the upper part of the
switch.
Note: Do not shift the axle to LO range with the vehicle in motion.
Split-shifting (combined axle and transmission shift - manual
transmissions only)
Ratio
combination
Transmission
gear
Axle range
To downshift the axle to a slower ratio and shift the transmission, shift
the transmission and move the control switch to the lower ratio before
the clutch is re-engaged.
To upshift the axle and shift the transmission, move the control switch
to a faster ratio and make the transmission shift in the usual manner.
Ratio extender use
Low End
A two-speed axle can be used as a ratio-extender when split shifting is
not necessary. For low end use, just shift the axle into the LO to start
out, and shift to HI when the extra torque is no longer needed.
Transmission
(5-speed)
Two-speed Axle
130
2004 F650/750 (f67)
Supplement
USA English (fus)
Split-shift sequence
1 2 3
1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 6th 6th
LO HI LO
1st
Axle
Low
4 5 6
HI LO HI
1st 2nd
7 8 9
LO HI LO
3rd 4th 5th
Axle High
10 11
LO HI
6th