Electrical Operation and Power Flow

GENERAL INFORMATION
This model has an electronic shift transfer case with three modes of operation: two-wheel drive range, four-wheel drive high range and four-wheel drive low range. Gear reduction for low range is provided by a planetary gear set. The floor-mounted shifter has been eliminated on vehicles equipped with this transfer case. A switch located on the upper right side of the instrument panel is used to select the operating range. Indicator lamps on the switch show the current mode of operation.

When four-wheel drive has been selected, the four-wheel drive indicator lamp on the switch is designed to come on when the front axle has engaged. The lamp will blink while the front axle is engaging. This is normal.

This model has a two-piece aluminum case containing front and rear output shafts, two drive sprockets, an electronic shift mechanism, and a planetary gear assembly. The drive sprockets are connected and operated by the drive chain. The planetary gear assembly consists of a 4-pinion planetary carrier and an annulus gear that provide the four-wheel drive low range when engaged. The reduction ratio is 2.72:1 in this range. The electronic shift mechanism is controlled by an electronic shift encoder motor mounted on the front half of the transfer case.

IDENTIFICATION

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An identification tag is attached to the rear half of the transfer case. This tag provides the transfer case model number, low range gear reduction ratio, and assembly number. The information on this tag is necessary when servicing this transfer case. If the tag is removed or becomes dislodged during service operations, be sure to keep the tag with the unit.

POWER FLOW
In all drive range positions input torque is transmitted to the transfer case gear chain through the transfer case/input gear. In 2HI range, torque flows from the input gear to the range shift hub and mainshaft. Torque flow continues through the slip yoke which is splined to the mainshaft, and finally to the rear propeller shaft and axle. The mode synchronizer remains in the neutral position and does not lock the drive sprocket to the mainshaft. As a result, torque is not transferred to the driven sprocket.

In 4HI range, input torque from the input gear is transmitted to the mainshaft in exactly the same fashion as in 2HI range. However, in the 4HI position, the mode synchronizer sleeve is shifted into engagement with the clutch teeth of the drive sprocket. This locks the drive sprocket to the mainshaft through the synchronizer. Torque is transmitted through the drive sprocket to the driven sprocket by the connecting drive chain. The torque flows through the front output shaft to the front propeller shaft and axle resulting in high range four-wheel drive.

In 4LO range, the path of torque through the transfer case is exactly the same as in 4HI range but with one major difference. In 4LO range the range shift hub is shifted into engagement with the planetary carrier. This causes the input gear to rotate the planetary pinions inside the annulus gear, causing the planetary carrier, range shift hub, and mainshaft to rotate at a gear reduction ratio of 2.72:1.