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Equipment Operator Basic - Beginning construction equipment operators manual | Next
Propeller Shaft Assemblies |
R-REVERSE POSITION.— Some shift levers
must be raised slightly to be moved to the R or reverse
position. Others may require the depressing of a button
on the end of the lever before moving to R.
Become thoroughly familiar with the operator’s
manual, vehicle instruments, controls, and selector
positions before operating a vehicle or piece of
equipment. You may operate equipment that has the
R-reverse position on the extreme right on some shift
selectors, on the extreme left on others, and the
intermediate position on others. From a force of habit,
when you are in a different vehicle from the one you
have been operating, you could move the selector lever
to R, thinking you were moving it to D or L, and cause
the vehicle to move in an entirely opposite direction than
anticipated.
AUXILIARY TRANSMISSION
Auxiliary transmissions are mounted on the rear of
the regular transmission to provide more gear ratios.
Most auxiliary transmissions have only a L-low and a
H-high (direct) range in a transfer assembly. The low
range provides an extremely low gear ratio for hard
pulls. At all other times, the high range should be used.
Gears are shifted by a separate gearshift lever in the
driver’s cab (fig. 2-10).
Transfer Cases
Transfer cases are placed in the power trains of
vehicles driven by all wheels (fig. 2-11). Their
purpose is to provide the necessary
additional propeller-shaft connections
wheels.
offsets for
to drive the
Transfer cases in heavier vehicles have two-speed
positions and a declutching device for disconnecting the
front driving wheels.
Two-speed transfer cases also
serve as auxiliary transmissions.
Transfer cases are quite complicated. When they
have speed-changing gears, declutching devices, and
attachments for three or more propeller shafts, they are
even larger than the main transmission.
Some transfer cases have an overrunning sprag unit
(or units) on the front output shaft. A sprag unit is a form
of a overrunning clutch; power can be transmitted
through it in one direction but not in the other. During
normal operation, when both front and rear wheels turn
at the same speed, only the rear wheels drive the vehicle.
Figure 2-10.—Auxiliary transmission.
Figure 2-11.—Transfer case installed in a four-wheel
drive truck.
2-8
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