The transfer case is used to provide power flow from the transmission to the front axle. The transfer case also provides a way of disconnecting the front axle in order to provide better fuel economy and quieter operation when the vehicle is driven on roads where the four-wheel drive is not required. The transfer case provides an additional gear reduction when placed in low range. This is useful when driving in difficult off-road conditions. The New Venture Gear model NVG241 manually shifted transger case is used on four-wheel drive vehicles under 9200 lb GVW (K1 and K2).

The models NVG241 is an aluminum case, chain driven unit with four modes of operation:

A planetary gear set provides the reduction gearing for the low range.

A floor mounted shift lever is used in order to select the operating range for the NVG241 transfer case. The indicator lamps on the floor console show the current mode of operation. The four wheel drive indicator lamp illuminates whenever the front axle is engaged. After selecting four wheel drive from the two wheel drive position, a slight delay for the front axle indicator lamp to illuminate is normal.

Two Wheel Drive Operation

When the transfer case is in the two wheel drive range, the torque flows from the input gear to the range shift hub and the main shaft, through the propeller shaft to the rear axle.

2HI to 4HI

The system consists of a control module mounted in a relay socket under the hood, and an electromagnetic clutch inside the transfer case. The clutch replaces the conventional blocker wing. When energized, the clutch provides synchronization, resulting in a smooth shift. When the transfer case lever is moved to the 4HI or 4LO position, the current is supplied to the Timer Logic and Relay Module, which controls the application of power to the synchronizer and the front axle actuator.

Important: The front axle indicator lamp does not illuminate until the front axle is fully engaged.

Shifting from 2WD to 4WD causes the following sequence of actions to occur:

1. Operation of the shift linkage engages fhe front propeller shaft.
2. Operation of the shift linkage also closes a switch in the transfer case. That switch applies ground to the control circuit of the front axle actuator.
3. The front axle actuator uses an electric motor to engage the right axle output shaft to the front axle differential.
4. When the front axle is fully engaged, the actuator closes a switch causing the 4WD indicator lamp to illuminate.

Four Wheel Drive High Range Operation

The torque flows from the input gear to the mainshaft the same as in the 2WD operation. The shift to 4WD causes the synchronizer sleeve to engage with the clutch teeth of the drive sprocket. This locks the drive sprocket to the mainshaft through the synchronizer sleeve. The torque is transmitted through the drive sprocket and the drive chain to the driven sprocket and the output shaft. The torque then flows through the front propeller shaft to the front axle.

4HI to 2HI

If the shift lever is moved back to the 2HI position, the operations in the preceding steps are reversed. The actuator motor operates in the opposite direction to disengage the right front axle from the front differential. This opens a switch extinguishing the 4WD indicator lamp.

Four Wheel Drive Low Range Operation

When the transfer case is shifted into the 4LO position, the torque flow and the operation is similar to the 4HI range, except that the range shift hub engages the planetary carrier. The planetary gear set then provides a gear reduction to the front and the rear axles.

In vehicles equiped with automatic transmission, the transfer case closes another switch which applies ground to a terminal of the VCM or PCM for transmission control.