The vehicles described use one of two types of transfer case. Vehicles with electric shift control have a New Venture Gear NVG 226 transfer case. The transfer case with electric shift control has five modes: high range with two-wheel drive, high range with four-wheel drive, low range with four-wheel drive, neutral position and automatic four-wheel drive (A4WD).
Also, the described vehicles can use a single-speed automatic transfer case NVG 126. This box is constantly engaged in the automatic all-wheel drive mode.
It is not recommended to perform repair procedures on the transfer case yourself. It should be noted that repairs are extremely difficult to perform without the use of special equipment and devices. Furthermore, purchasing and installing a remanufactured replacement transfer case may be more cost effective than repairing the existing unit yourself, since repairs involve inspecting, adjusting, and replacing many parts and components, as described in this chapter.
S4WD (Steering Four Wheel Drive)
This system provides the ability to choose one of four modes (two-wheel drive upshift, all-wheel drive upshift, all-wheel drive downshift, neutral position), and an additional (fifth) automatic all-wheel drive mode (A4WD). Switching modes occurs with electronic control.
When selecting one of the modes (by pressing the switch located on the instrument panel) the corresponding signal is sent to the transfer case switching unit, and the gearshift lever is turned by a servomotor (clockwise or counterclockwise). Thus, the transfer case switches to the required mode. After a certain transfer case mode is engaged, a signal to engage the front axle is received from the transmission control unit. The transfer case transmitter, located on the servomotor, serves to transmit a signal to the transmission control unit that corresponds to the position of the gear shift lever. The transfer case also has a servomotor locking device, which ensures that the selected mode is fixed. When the A4WD button is pressed, the servo motor lock remains in adaptive mode, so it can be unlocked or locked according to which drive pattern is adopted in the transfer case switching unit: two-wheel drive or four-wheel drive.
When the automatic all-wheel drive (A4WD) mode is engaged, the transmission switches to a high-range all-wheel drive mode, but at the same time, the connection of its internal clutch varies depending on changing road conditions. When signals are received by the transfer case switching unit that detect wheel slippage (signals come from vehicle speed sensors located on the front and rear secondary shafts of the transfer case) a signal to turn on the servomotor comes from the switching unit, and the clutch is pressed. In this way, the torque is transmitted to the front output shaft of the transfer case. When a signal corresponding to the rotation of the wheels on the front and rear axles is received by the switching unit, it is sent from there to the servomotor, and the clutch is disengaged. The transmission reverts back to two-wheel drive mode.
The NVG 226 transfer case also has a neutral position mode. When this mode is selected, the gearbox and transfer case are excluded from the kinematic diagram when towing the vehicle, which prevents unnecessary load application to these units.
Automatic All-Wheel Drive (A4WD)
This system is used in the NVG 126 transfer case. The system works similarly to the corresponding system in the NVG 226 box. The difference is that in the NVG 126 box the automatic all-wheel drive mode is always on and is the only possible one.