TM 9-2320-283-10
a. Driving at Highway Speed:
When driving conditions permit, maintain the legal highway speed in gear range
1-5. This permits running the engine below governed speed (preferably 10 to
20 percent below governed speed). This is the engine’s cruising range and it
affords better fuel economy than higher engine speeds. Recommended normal
highway cruising range is 1,800 to 1,900 rpm.
Operate in the economy range at full throttle if you are satisfied with the way
the vehicle performs, However, there are times when hilly terrain, high winds
or other conditions make it impractical to operate without reserve power. Such
conditions are better met if the truck is operated in a lower gear range such as
1-4 where reserve power is available for changes in terrain, wind, and traffic
conditions.
b. Driving in the City:
Operate the truck in gear range 1-5 or 1-4 for normal city driving. This will keep
engine rpm’s to a minimum and give greatest fuel economy. If traffic, road, or
load conditions are extreme, you may find it desirable to limit the automatic
upshifting to a lower gear range. In such cases, you may use gear range 1-3,
but upshift by moving the shift lever to 1-4 or 1-5 as soon as conditions allow,
for best economy.
The transmission can be downshifted or upshifted manually, even at full throt-
tle. Although there is no speed limitation on upshifting, there is on downshifting
and Reverse. Manual downshifting should be avoided when the vehicle is above
the maximum speed attainable in the next lower gear. Protection against improper
downshifts and reverse shifts is provided, however, in the design of the transmis-
sion hydraulic system. If a downshift or reverse shift is made manually at too
high a speed, the hydraulic system automatically prevents the shift from taking
place until a safe lower speed is reached.
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