Low Range (fig. 5-29) - When using the low range in the transfer case, the sliding gear on the transmission main shaft is disengaged from the constant mesh gear and engaged with the idler gear on the idler shaft. This design reduces the speed by having the sliding gear mesh with the larger idler gear. The shifting linkage on some vehicles is arranged so shifting into low range is possible only when the drive to the front axle is engaged. This design prevents the operator from applying maximum torque to the rear drive only, which can cause damage.
POSITIVE TRACTION TRANSFER CASE
The positive traction transfer case is very similar to the conventional transfer case - the basic difference being that a sprag unit has been substituted for the hand-operated sliding clutch on the front output shaft.
A sprag unit is a steel block shaped to act as a wedge in the complete assembly. In the sprag unit there are 42 sprags assembled into an outer race and held into place by two energizing springs (fig. 5-31). The springs fit into notches in the ends of the sprags and hold them in position. The outer race is the driven gear on the front output shaft. The inner race is on the front output shaft itself.
On these units, the transfer case is designed to drive the front axle slightly slower than the rear axle. During normal operation, when both front and rear wheels of the vehicle are turning at the same speed, the outer race of the sprag unit (in the driven gear) turns slower than the inner race (on the output shaft). This design prevents the sprags from wedging between the races. No lockup occurs and the front wheels turn freely; they are not driven (fig. 5-32). However, if the rear wheels should lose traction and begin to slip, they tend to turn faster than the front wheels; the outer race tends to turn faster than the inner race. When this happens, the sprags wedge or jam between the two races and the races turn as a unit to provide power to the front wheels (fig. 5-32).
Figure 5-31. - Transfer case sprag unit.
The fluid level in a transfer case should be checked at recommended intervals. To check the lubricant level, remove the transfer case fill plug, which is normally located on the side or rear of the case. The lubricant should be almost even with the fill hole. If required, add the recommended type and amount.
The first indication of trouble within a transfer case, as with other components of the power train, is usually noisy operation. If an operator reports trouble, make a visual inspection before removing the unitContinue Reading