AUXILIARY TRANSMISSIONS, SUBTRANSMISSIONS, AND OVERDRIVES
Section I. AUXILIARY TRANSMISSIONS
them because a low-speed range is available for pulling
26-1. Purpose. An auxiliary transmission (fig. 26-1) is
power and a high-speed (direct-drive) range is available
used to compound the number of gear ratios that are
for highway usage.
available from the main transmission. It usually is a
separate two-speed transmission that mounts in series
26-2. Operation (Fig. 26-2). The auxiliary transmission
between the transmission and the driving axle by utilizing
two propeller shafts. By providing two speeds, the
is controlled by a lever in the driver's compartment. The
auxiliary transmission effectively will double the number
gear ratios usually are selected in the box by a sliding
of gear ratios available from the main transmission.
dog clutch. The gear ratios of the auxiliary transmission
Vehicles equipped with auxiliary transmissions generally
must be selected while the vehicle is not in motion.
are more versatile than vehicles without
Figure 26-1. Typical Location of Auxiliary Transmission.