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 casethe 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.
TRANSFER CASE MAINTENANCE
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 unit