DESCRIPTION & OPERATION
The New Venture Gear (NVG) 261, RPO NP2 transfer case is a 2-speed, part-time with "mode shift-on-the-fly" capability. It has a chain driven front output shaft and an epicyclical low range planetary arrangement. The NVG 261 transfer case features a 4 position shift lever control located in the vehicle floor plan. As required, the operator can select 4HI position from 2HI "on-the-fly", as described in the owners manual. A dash 4WD lamp will continue flashing during shifting, until all criteria have been met and new mode/range position has been reached. Once new mode/range position is fully engaged and front axle disconnect locks in, the dash light 4WD indicator lamp will remain ON constantly. Range shifting functions similarly, although it should be limited to speeds of 5 MPH or less.
The 4 manual mode, or range gear positions, of the NVG 261 transfer case are
- 2HI - 2 wheel drive high range. See «2WD MODE POWER FLOW»(ref-160326-S00583544542004020900000) .
- 4HI - 4 wheel drive high range, part-time. See «4HI MODE POWER FLOW»(ref-160326-S35667915022004020900000) .
- 4LO - 4 wheel drive low range, 2.72:1 gear ratio reduction. See «4LO MODE POWER FLOW»(ref-160326-S25338504962004020900000) .
- N - Neutral, 4 wheel. See «NEUTRAL MODE POWER FLOW»(ref-160326-S10888145522004020900000) .
When ignition switch is placed in RUN position and 4WD shift lever is in 4WD position, the transfer case switch closes, supplying a ground to the axle actuator control circuit. With ground applied, the logic of the front axle actuator actuates a DC motor to engage the front axle and supply voltage to the axle switch signal circuit. The axle switch signal circuit notifies the Powertrain Control Module (PCM) and the Anti-Lock Brake System (ABS) that the vehicle is in the 4WD mode. The 4WD indicator is commanded on via a Class 2 serial data signal from the PCM. When the 4WD shift lever is in the 4WD low range position, the transfer case switch closes and supplies a ground on the 4WD low signal circuit. This informs the PCM that the vehicle transfer case is in low range. When the vehicle is in low range, the PCM changes the shift pattern of the automatic transmission.
During normal driving situations, the transfer case can operate in the 2WD mode. The driver may choose to select any of the mode/range gear positions while driving the vehicle. However, the transfer case should not be shifted into or out of 4LO unless the following criteria have been met
- The automatic transmission is in neutral or the clutch pedal is depressed.
- The vehicle speed is less than 3 MPH.
This transfer case also has a neutral position. A shift to the neutral position allows the vehicle to be towed without rotating the transmission output shaft. In the neutral position, the rear propeller shaft will rotate the transfer case rear output shaft, in turn rotating the oil pump, providing constant lubrication during towing. This Neutral position is a 4WD neutral, meaning the front and rear outputs of the transfer case are engaged as though in 4HI. With a disconnecting front axle, there is no power flow to the front wheels, allowing towing with the front wheels off the ground or flat towing without driveline binding. Again, the transfer case should not be shifted into or out of neutral unless the following criteria have been met
- The automatic transmission is in neutral or the clutch pedal is depressed.
- The vehicle speed is less than 3 MPH.
The NVG 261 transfer case is available in 5 variations, depending on the engine and transmission configurations. (Scheme 19) The variations allow the transfer case to handle different torque loads. When servicing the transfer case it is important to understand which variation is being serviced because of the difference in parts.
Scheme 19
There are some product improvement changes being released during the model year. The early production transfer case has a separate cup plug and a needle bearing in the input gear. The later production transfer case has a new input gear and uses a cup plug style bearing. The oil pump on the LD, HD1, and HD2 version is being changed to be the same as the SHD version. This oil pump change also includes a new rear output shaft. When servicing an early release model, only the later release parts will be available.
The HD2 and the SHD model share many of the same components but the increased torque capacity of the SHD requires a double row input bearing, larger diameter rear output shaft, rear output shaft bearing higher capacity, larger rear seal, case halves machined differently, and a different speed reluctor wheel.