R-REVERSE POSITION.— Some shift leversmust be raised slightly to be moved to the R or reverseposition. Others may require the depressing of a buttonon the end of the lever before moving to R.Become thoroughly familiar with the operator’smanual, vehicle instruments, controls, and selectorpositions before operating a vehicle or piece ofequipment. You may operate equipment that has theR-reverse position on the extreme right on some shiftselectors, on the extreme left on others, and theintermediate position on others. From a force of habit,when you are in a different vehicle from the one youhave been operating, you could move the selector leverto R, thinking you were moving it to D or L, and causethe vehicle to move in an entirely opposite direction thananticipated.AUXILIARY TRANSMISSIONAuxiliary transmissions are mounted on the rear ofthe regular transmission to provide more gear ratios.Most auxiliary transmissions have only a L-low and aH-high (direct) range in a transfer assembly. The lowrange provides an extremely low gear ratio for hardpulls. At all other times, the high range should be used.Gears are shifted by a separate gearshift lever in thedriver’s cab (fig. 2-10).Transfer CasesTransfer cases are placed in the power trains ofvehicles driven by all wheels (fig. 2-11). Theirpurpose is to provide the necessaryadditional propeller-shaft connectionswheels.offsets forto drive theTransfer cases in heavier vehicles have two-speedpositions and a declutching device for disconnecting thefront driving wheels.Two-speed transfer cases alsoserve as auxiliary transmissions.Transfer cases are quite complicated. When theyhave speed-changing gears, declutching devices, andattachments for three or more propeller shafts, they areeven 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 formof a overrunning clutch; power can be transmittedthrough it in one direction but not in the other. Duringnormal operation, when both front and rear wheels turnat the same speed, only the rear wheels drive the vehicle.Figure 2-10.—Auxiliary transmission.Figure 2-11.—Transfer case installed in a four-wheeldrive truck.2-8
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