All-wheel drive control system and transfer case (Chevrolet Tahoe 2)

There were several all-wheel drive schemes on the GMT800 and GMT900 platforms. Models with permanent all-wheel drive (Full Time), models with a pluggable front axle (Part Time), and also a system of automatic connection of the front axle (Auto 4WD). Therefore, during the history of the two platforms, various transfer boxes from two manufacturers Borg Warner and New Venture Gear were used depending on the configuration and year of manufacture. Sometimes the manufacturer designates the Full Time system as AWD (All Weel Drive). The peculiarity of gearboxes for these American cars can be considered that all control is electronic, with the help of switches and drives. There are practically no classic all-wheel drive control handles.

GMT800 Platform

Escalade models used New Venture Gear model NVG 149 (RPO NP3) gearboxes for a very short time, which were single-stage, operating according to the Full Time scheme. The gearbox provided torque distribution under normal road conditions between the front and rear axles in a ratio of 32:68. When the wheels of the rear or front axle slip, the center differential, using the viscous clutch of the transfer case, provides torque distribution to the "non-slipping" axle up to 100% (i.e. the interaxle differential is locked).

When the front axle slips

When the rear axle slips

The most popular transfer case BW 4481 (PRO NR3) by Borg Warner provided the scheme of the all-wheel drive system Full Time. The box was also single-stage and provided the distribution of torque between the front and rear axles in the ratio of 40:60. It was installed on Cadillac Escalade GMT800 cars from 2003 to 2006 together with the system of course stability (VSES). But the box does not have an interaxle differential, and the distribution of torque remains constant.



Early Tahoe GMT800 series used a single 261 transfer case (PRO NP2) with switching between 2WD and 4WD modes using control levers in the cabin. The box had 3 modes 2WD, 4HI and 4LO. But on models produced since 2001, it was removed from the package.



Since 2001, a New Venture Gear NVG 263 transfer case has also been installed, which provides a Part Time all-wheel drive scheme. The transfer case provides three operating modes: 4Hl, 4LO, 2HI. Switching between modes is also carried out using switches located on the dashboard.

The 2001-2006 Tahoe GMT800 primarily used the New Venture Gear model NVG 246 (RPO NP8) transfer case. It is a two-speed gearbox with an automatic torque distribution system. The instrument panel contains the all-wheel drive control switches. The transfer case provides five operating modes: Auto 4WD, 4Hl, 4LO, 2HI and N (neutral). Under normal driving conditions, the Auto 4WD mode is used. The control system monitors rear wheel slippage based on signals from the front and rear driveshaft speed sensors. If rear wheel slippage occurs, the system redistributes torque (increases the speed of rotation of the front wheels) up to the rotation speed of the rear wheels via a clutch. The other modes are classic.







Unlike the BW 4481 (PRO NR3) transfer case installed on the Escalade model, the BW 4482 transfer case is a two-stage one and provides a Full Time all-wheel drive system with torque distribution within the same 40:60 limits under normal conditions (4HI mode). Using switches, it is possible to select 4HI, 4LO modes (low gear). There is also a neutral position on the transfer case. Like the BW 4481 box, the 4482 transfer case was installed on cars with the VSES stability control system. The VSES switch is located on the transfer case control panel. When the VSES system is operating, not only the ABS system elements are activated (rotation speed sensors, modulator, etc.), but also controls the transfer case.

GMT900 Platform

The new platform models featured the NVG 246 RPO NP8 transfer case used on the GMT800 platform. In keeping with the complete interior makeover of the new models, the 4WD control switches also received a new look.

A Borg Warner (BW) model 4485 NR3 transfer case was also installed (single-stage, planetary transfer case), providing torque distribution between the front and rear axles in a ratio of 40:60 (Full Time or AllWheel Drive (AWD)). The new transfer case is not much different from the BW 4481 model used on the GMT800 platform.