Lesson 2/Learning Event 2
Final drives used in most military tactical vehicles are either single- or double-reduction
units. Single-reduction axles are used on light wheeled vehicles and consist of one set of
reduction gearing, and these same gears also change the direction of power flow. The
double-reduction units have a second set of reduction gears. Double-reduction final
drives are used on heavy wheeled vehicles where a large amount of reduction is needed.
FIGURE 14. WORM GEAR.
Some early vehicles, built to haul heavy loads, used a worm-gear final drive. This type
gearing provided a large amount of reduction and worked well for heavy, slow-moving
trucks. The gearing consisted of a worm and a worm gear. This type gearing creates a
lot of friction between the gear and at the end of the worm. It is not adaptable to the
high-speed operation of modern vehicles.