Humorous Story and Question

[Joseph Garcia]

Hi Folks,

I thought that I'd share a humorous story with you, and then ask for your thoughts and perspectives on a question that came out of this story.

Story:

I get a call from, my oldest son asking if my Yukon is available to assist him with a problem. I say sure and ask him what the problem is. He tells me that he's trying to cut down a large maple tree in his yard that is too close to his house. So, in order to ensure that the tree does not fall in the direction of his house, he was going to use his pickup truck as an anchor, and attach ropes from the truck to the tree, prior to taking the chain saw to the tree.

He is in the process of re-leveling and re-landscaping his back yard area for better drainage, and the area was all torn up as part of the re-leveling project. So, it was not going to be an issue driving the truck over that area, to get it in the proper position to serve as an anchor. Or, was it.....

So, I get my tow strap and head over to his house to help him get his truck out of the mud. On the way over, I text my youngest son to tell him what I am doing, and he texts back, "ROFL!! Sending a GM luxury SUV over to pull a fully feature loaded Ford F250 pickup truck out of the mud! Priceless!!"

Anyway, we did get his truck out of the mud, and my oldest son is quite humbled by the experience.


Question:

In our first attempt to rescue my son's truck, we simply put the tow strap on the receiver balls of both trucks, my son puts his truck in 2 wheel (rear) drive and in reverse, and we try to pull the truck out of the mud. His truck's rear tires start to spin, and my truck's rear tires start to spin and dig into the mud, and we realize that this is not going to work.

So for, our second attempt, we dig out the mud from behind his front tires and place long wood planks under the back edge on the front tires, my son puts his truck in 4 wheel drive and in reverse, and we successfully pull his truck out of the mud.

My question here is that on our first and failed attempt, my Yukon's rear tires started to spin and dig into the mud, but there was no evidence of any spinning of my Yukon's front tires. I would have though that with AWD, I would have seen evidence of spinning of all 4 tires. On that attempt, I started with the transmission in manual 1st gear, but then I later switched the transmission to automatic 'D' position. In neither case, did I see any evidence of the front tires spinning.

Is this normal or expected behavior of the Yukon's AWD in this scenario? Is there something that I should have done to force power to all 4 tires in this scenario?

Your thoughts and perspectives are most welcome.

 

[Doubeleive]

the power split is not 50/50, not sure what it is exactly I think it is 60/40 or something of that nature, Could have been traction control taking over if you did not have that disabled. Traction control and driving in mud do not mix well, if you put it up on 4 jack stands and put it in drive all 4 wheels should spin.
I am sure some one else with more knowledge will chime in.

 

[gooffeyguy]

The torque split is 60/40 on the awd transfer case. I think your problem had to do with traction control and Stabilitrak still on

Sent from my SM-G930V using Tapatalk

 

[kbuskill]

Not 100% sure about these trucks but the older trucks used a viscous coupling inside the AWD transfer case and the rear tires would have to spin up to a certain speed/rpm before the viscous coupling would really transfer power to the front wheels. I have heard of guys partially setting the parking brake to put some resistance on the rear wheels in order to transfer power to the front wheels. I seriously doubt this is good for the transfer case or the brakes for that matter.

I know that on the regular 4wd trucks, of this Gen, that in order to get full power to the wheels the ABS has to be disabled by pulling the ABS fuse (#9 if memory serves). If not the Stabilitrac and Traction control will over ride things. Turning the ST and TC off with the buttons doesn't cut it. There are videos on the tube that show this fuse method in action.

 

[avalonandl]

Your first issue is you need extra weight. A 24 pack of Budweiiser

 

[Rocket Man]

Your first issue is you need extra weight. A 24 pack of Budweiiser

Or 2 fat chicks sitting in the third row AND a 24 pack of Budweiser in your gut which makes the fat chicks look hot.

 

[CaptainAmerica1]

Nvm…

 

[adventurenali92]

Not 100% sure about these trucks but the older trucks used a viscous coupling inside the AWD transfer case and the rear tires would have to spin up to a certain speed/rpm before the viscous coupling would really transfer power to the front wheels. I have heard of guys partially setting the parking brake to put some resistance on the rear wheels in order to transfer power to the front wheels. I seriously doubt this is good for the transfer case or the brakes for that matter.

I know that on the regular 4wd trucks, of this Gen, that in order to get full power to the wheels the ABS has to be disabled by pulling the ABS fuse (#9 if memory serves). If not the Stabilitrac and Traction control will over ride things. Turning the ST and TC off with the buttons doesn't cut it. There are videos on the tube that show this fuse method in action.

This is only partially true. The actual pick up trucks in the GMT800 platform that were AWD had a viscous couple in the transfer case, however the AWD SUV variants did not have the viscous coupler transfer case, it’s a different set up.

 

[Rocket Man]

This is only partially true. The actual pick up trucks in the GMT800 platform that were AWD had a viscous couple in the transfer case, however the AWD SUV variants did not have the viscous coupler transfer case, it’s a different set up.

That depends. My NVG149 TC has a viscous coupler.

 

[adventurenali92]

That depends. My NVG149 TC has a viscous coupler.

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

 

[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