Humorous Story and Question

[Bill 1960]

With any AWD transfer case, unless you have an explicit locking mechanism (such as the 4x4 transfer case), what you have is a differential. Just as in the front and rear axles.

What happens with a diff when one tire has more traction than the other? One wheel peel. The side with less traction spins. The side with greater traction doesn’t spin, although equal torque is applied.

The center diff is exactly the same. Whichever end of the vehicle has the least traction will spin. Yes, there’s often a bias such as 60/40 built in due to uneven weight distribution but nonetheless one end or the other will break traction first.

The only way to get the holy grail of off-road bliss, so-called “true four wheel drive “ is lockers in the center, in the front diff, and the rear diff. Then all the wheels rotate at the same speed and either none slip, or they ALL do.

Vehicle designers simulate this effect with varying degrees of success using traction control.

TLDR; normal operation.

 

[Rocket Man]

Well that’s because you have a 2002 lol I think it changed in 2003.

Yes they did. They were the NVG149 in 99-02, and the BW4482 in 03-06. So a little under half the NBS AWD’s had a viscous coupler. Here’s info on the 03-06 AWD transfer case, not sure about the 07-14 but I believe they’re the same. This is from GM:




The Borg Warner (BW) model 4481, RPO NR3 transfer case is a one-speed, full time, all wheel drive (AWD), transfer case. The transfer case provides power to both axles, through an external planetary type differential, which has two different sets of pinion gears. The planetary differential provides a 40/60 torque split, front/rear, full time. This means both axles are constantly being driven for maximum traction in all conditions.

The transfer case external type planetary differential functions the same as a typical rear axle differential. The transfer case differential pinion gears function as the spider gears, and the sun gears function as the side gears.

The following actions occur because of the planetary differential:

•If the vehicle is on a hoist, the front propeller shaft can be rotated by hand.
•The vehicle cannot be driven if one propeller shaft is removed.
•Operating the vehicle on the hoist can damage the differential pinion gears, by over-spinning.
•Operating the vehicle with one propeller shaft removed causes over-spinning of the differential pinion gears.
The BW 4481 design of the planetary differential allows the use with the Vehicle Stability Enhancement System (VSES) vehicles. The VSES takes use of the planetary differential, by applying braking to a tire that has less traction and dividing the engine torque to the other axle.

The BW 4481 case halves are high-pressure, die-cast magnesium. Ball bearings support the input shaft, the front output shaft, and the rear output shaft. The transfer case requires DEXRON®III ATF GM P/N 12378470 (Canadian P/N 10952622), which is red in color.

 

[Rocket Man]

With any AWD transfer case, unless you have an explicit locking mechanism (such as the 4x4 transfer case), what you have is a differential. Just as in the front and rear axles.

What happens with a diff when one tire has more traction than the other? One wheel peel. The side with less traction spins. The side with greater traction doesn’t spin, although equal torque is applied.

The center diff is exactly the same. Whichever end of the vehicle has the least traction will spin. Yes, there’s often a bias such as 60/40 built in due to uneven weight distribution but nonetheless one end or the other will break traction first.

The only way to get the holy grail of off-road bliss, so-called “true four wheel drive “ is lockers in the center, in the front diff, and the rear diff. Then all the wheels rotate at the same speed and either none slip, or they ALL do.

Vehicle designers simulate this effect with varying degrees of success using traction control.

TLDR; normal operation.

The NVG149 with the viscous coupler is different. I have a hard time getting a wheel to spin, on wet roads with a supercharger, cam, headers, etc. It really hooks up. Also great in the snow or on sand. This is why I don’t understand why they changed.

 

[gooffeyguy]

Yes they did. They were the NVG149 in 99-02, and the BW4482 in 03-06. So a little under half the NBS AWD’s had a viscous coupler. Here’s info on the 03-06 AWD transfer case, not sure about the 07-14 but I believe they’re the same. This is from GM:




The Borg Warner (BW) model 4481, RPO NR3 transfer case is a one-speed, full time, all wheel drive (AWD), transfer case. The transfer case provides power to both axles, through an external planetary type differential, which has two different sets of pinion gears. The planetary differential provides a 40/60 torque split, front/rear, full time. This means both axles are constantly being driven for maximum traction in all conditions.

The transfer case external type planetary differential functions the same as a typical rear axle differential. The transfer case differential pinion gears function as the spider gears, and the sun gears function as the side gears.

The following actions occur because of the planetary differential:

•If the vehicle is on a hoist, the front propeller shaft can be rotated by hand.
•The vehicle cannot be driven if one propeller shaft is removed.
•Operating the vehicle on the hoist can damage the differential pinion gears, by over-spinning.
•Operating the vehicle with one propeller shaft removed causes over-spinning of the differential pinion gears.
The BW 4481 design of the planetary differential allows the use with the Vehicle Stability Enhancement System (VSES) vehicles. The VSES takes use of the planetary differential, by applying braking to a tire that has less traction and dividing the engine torque to the other axle.

The BW 4481 case halves are high-pressure, die-cast magnesium. Ball bearings support the input shaft, the front output shaft, and the rear output shaft. The transfer case requires DEXRON[emoji2400]III ATF GM P/N 12378470 (Canadian P/N 10952622), which is red in color.

I have the NR3 rpo code on my 2012 Denali

Sent from my SM-G930V using Tapatalk

 

[Bill 1960]

The NVG149 with the viscous coupler is different. I have a hard time getting a wheel to spin, on wet roads with a supercharger, cam, headers, etc. It really hooks up. Also great in the snow or on sand. This is why I don’t understand why they changed.

I’m pretty sure it was a cost decision, the VC is an expensive component. Perhaps some issues with long term reliability IDK specifically about that case but some other brands the viscous units torque transfer capacity degraded over time as wear took place.

The VC is nice because it’s acting essentially as an LSD in the center. Allows some slip but is always biased to try and match the shaft speeds front and rear.

 

[Rocket Man]

I’m pretty sure it was a cost decision, the VC is an expensive component. Perhaps some issues with long term reliability IDK specifically about that case but some other brands the viscous units torque transfer capacity degraded over time as wear took place.

The VC is nice because it’s acting essentially as an LSD in the center. Allows some slip but is always biased to try and match the shaft speeds front and rear.

I’m at 170k with power adders and it’s still kickin ass.

 

[Joseph Garcia]

Thank you all for your thoughts and perspectives. Very much appreciated.

My takeaway is that my truck's AWD is functioning as designed. The next time that I am in the shop, however, I'll have the mechanic lift all 4 wheels off the ground and confirm that all 4 wheels turn, when in Drive.

 

[Bill 1960]

Thank you all for your thoughts and perspectives. Very much appreciated.

My takeaway is that my truck's AWD is functioning as designed. The next time that I am in the shop, however, I'll have the mechanic lift all 4 wheels off the ground and confirm that all 4 wheels turn, when in Drive.

It would be much more entertaining to drive to the nearest off-road recreation spot and pin the throttle in a mud hole.

Please post pics and we’ll help you analyze the wheel speeds based on the mud spray patterns.

 

[Doubeleive]

It would be much more entertaining to drive to the nearest off-road recreation spot and pin the throttle in a mud hole.

Please post pics and we’ll help you analyze the wheel speeds based on the mud spray patterns.

YA, just be sure to hold the traction control button down for about 5 seconds first that will turn off traction control and stabiltrac