4WD/AWD

RyanZ71 · November 13, 2004

Just something that has got me thinking and wondering... I hear on the car commercials, mainly Subaru and Mercedies Benz claiming that they have the best AWD system out there... Is there really an AWD/4WD system that is better then the others or do they all do the same thing? "Transfering power from the wheels that slip to the wheels that grip" and "Sensors detect wheel spin and make adjustments" is what I hear alot of. I must admit that I think my old 89 Jeep Cherokee got me to more places in 4WD then have other 4WD vehicles I've driven but is there really a difference in the different auto makers AWD and 4WD systems?

Thanks,

Ryan

vhato · November 13, 2004

Yes,

And not all AWD drives systems are the same. GM's AWD is BASCIALLY an AutoTrac T-case without 4-Wheel Hi or 4-wheel Low and running in Auto all the time (Poor mans AWD...ie. SS, C3, some Astro Vans, etc). It transfers torque to one front tire (at a time..the one with least grip) and the rear axle. The rear diff decides which tire gets torque. Adding traction control to this system really improves it.

Systems that transfer torque from the wheels that slip to the wheels that grip add 4 wheel Traction control and Limited Slip differentials and some even electric differentials. These systems use the ABS sensors to determine what wheels are spinning higher that the others. The ABS system applies the brake to those spinning wheels which in return sends torque to the wheels that aren't spinning.

Thtese systems also incorporate a center differential that can engage/disenage by the computer or driver. Allowing for percentage based torque transfers from front to rear.

blue2kzr2 · November 13, 2004

As far as I know, the system in the AWD Astro/Safari, the Syclonce and the Tycoon are non-selectable AWD. That means that there no switch, it's just ON. I may be wrong, it's been known to happen before. However, the systems in the vehicles I mentioned above will NOT control each wheel individually, only alter the power distribution front to rear...

vhato · November 13, 2004

As far as I know, the system in the AWD Astro/Safari, the Syclonce and the Tycoon are non-selectable AWD. That means that there no switch, it's just ON. I may be wrong, it's been known to happen before. However, the systems in the vehicles I mentioned above will NOT control each wheel individually, only alter the power distribution front to rear...

<{POST_SNAPBACK}>

It is still like that.

Butch 02 Denali · November 13, 2004

Yes,
And not all AWD drives systems are the same. GM's AWD is BASCIALLY an AutoTrac T-case without 4-Wheel Hi or 4-wheel Low and running in Auto all the time (Poor mans AWD...ie. SS, C3, some Astro Vans, etc). It transfers torque to one front tire (at a time..the one with least grip) and the rear axle. The rear diff decides which tire gets torque. Adding traction control to this system really improves it.

Systems that transfer torque from the wheels that slip to the wheels that grip add 4 wheel Traction control and Limited Slip differentials and some even electric differentials. These systems use the ABS sensors to determine what wheels are spinning higher that the others. The ABS system applies the brake to those spinning wheels which in return sends torque to the wheels that aren't spinning.

Thtese systems also incorporate a center differential that can engage/disenage by the computer or driver. Allowing for percentage based torque transfers from front to rear.

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Sorry. that is incorrect.

GM's AWD in the SS, Sierra Denali's and Escalades uses the NVG149 transfer case. It uses a viscus coupling and is capable of instantly transferring 0-100% of engine power to the front or the rear, it's called biasing. The true positraction in the rear splits the traction duties again. This system is nothing like Autotrac, and is far superior to the computer controlled one that uses the abs braking to actually apply the brakes to the spinning wheel.

the blur · November 14, 2004

My AWD system in my 03 Denali is terrible compared to my AWD system in my 95 astro van. The 95 van had a direct coupling, or some other method that was more "positive" than the 03 Denali.

I have alreadly gotten stuck in 8" of snow with the Denali, and I could drive through 2 feet of snow with my astro van with posi rear.

the Denali only comes with an open diff, no limited slip, which is a serious flaw in winter traction.

Butch 02 Denali · November 14, 2004

My AWD system in my 03 Denali is terrible compared to my AWD system in my 95 astro van. The 95 van had a direct coupling, or some other method that was more "positive" than the 03 Denali.

I have alreadly gotten stuck in 8" of snow with the Denali, and I could drive through 2 feet of snow with my astro van with posi rear.

the Denali only comes with an open diff, no limited slip, which is a serious flaw in winter traction.

<{POST_SNAPBACK}>

I know. The Denali's changed to the open centerdiff/ABS controlled AWD in 2003 and i think they made a big mistake. The only trucks still using the NVG149, true AWD transfer case are like I said, the SS, all the SIERRA Denali's and the Escalade, though I'm not sure on the Escalade anymore.

BTW...The Astro used the same system used in the Syclone/Typhoon and was a viscus coupling just like the NVG149, just a little smaller. As you found out, this system performs incredibly in all conditions. I also have an Avalanche with Autotrac. Moving them out of my driveway so I can plow gave me a good chance for a side by side conmparison. In a foot of snow, the Autotrac was searching for traction, I could feel it. It was spinning and grabbing. It went, but with difficulity. Put it in 4wd hi, and it was about the same. Next the Sierra Denali. no slip, no grabbing, felt like I was on bare ground, it just went. It was like night and day! I played for a while before I got the plow out and cleaned up the mess.

You know, a NVG149 should bolt right in your Denali, I see them on Ebay once in a while. They were first used in the 2001 GMC C3, then the 2002-2005 Sierra Denali's, all Denali's up to 03 and any AWD Escalade so there are some in the boneyards now.

the blur · November 14, 2004

your saying the 03 Escalade has a different transfer case than my 03 denali??

I also have the stability system, which is a scaled down version of the corvette active handling. so maybe that's why they changed the transfer case??

I know the newer AWD astro vans are NOT as good in the snow because they changed the transfer case from viscous to something else.

I have to start reading about this. it must be the stability system that they use an open diff, and lousy transfer case. I have to get new tires on my denali only because of the snow. if the AWD was better, I Could get another year out of my tires...

8100HD · November 14, 2004

I'll throw another ball into play here...I have a '04 Tahoe with the stabilitrac system on it..what sets it apart from the Denali and Escalade is that I have the option of 4whl Low...along with Awd..I must say that this truck is amazing in the snow..better than my HD without a doubt...was out playing in the fluffy stuff last winter and it is very hard to get the truck sideways, corrects itself quickly.

Xao · November 15, 2004

I see everyone talking about the SUV and Minivan line ups, how do the '04 Silverado Z71's line up with this?

I'm looking forward to winter driving in my new truck. I'm half tempted to drive out to CO to go four wheeling in the mtns, errrr, I mean to see the family.

RyanZ71 · November 16, 2004

Today I saw a GMC Savanna Van 1500 and on the back of it it said AWD When did the full size GM Vans get AWD? Is the AWD system on these full size vans any good?

Butch 02 Denali · November 16, 2004

Today I saw a GMC Savanna Van 1500 and on the back of it it said AWD When did the full size GM Vans get AWD? Is the AWD system on these full size vans any good?

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I'm not sure what system they use, If anyone can get the model number of the transfer case we can tell though.

Butch 02 Sierra Denali

JoeTahoe · November 17, 2004

My AWD system in my 03 Denali is terrible compared to my AWD system in my 95 astro van. The 95 van had a direct coupling, or some other method that was more "positive" than the 03 Denali.

I have alreadly gotten stuck in 8" of snow with the Denali, and I could drive through 2 feet of snow with my astro van with posi rear.

the Denali only comes with an open diff, no limited slip, which is a serious flaw in winter traction.

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Since I am in the process of trying to replace my '99 Tahoe with an '03 Denali, this is depressing to read. I was under the impression that AWD + StabiliTrak on an '03 Denali would make our Ontario winters child's play. Now I am wondering if I should try to get an '04 Tahoe with StabiliTrak instead of an '03 Denali.

mcreyaufmiller · November 17, 2004

I personally do not like the full time AWD systems. I perfer to control this myself. It would seem to me that with the Full time AWD, the sytstem could fail and lock you in AWD on a dry road and really screw the entire thing up. They have yet to fully perfect the 4x4 systems to date, they lock-up all the time, as indicated from other threads here.

Mike

Butch 02 Denali · November 17, 2004

I personally do not like the full time AWD systems. I perfer to control this myself. It would seem to me that with the Full time AWD, the sytstem could fail and lock you in AWD on a dry road and really screw the entire thing up. They have yet to fully perfect the 4x4 systems to date, they lock-up all the time, as indicated from other threads here.

Mike

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Mike, the AWD IS always in, there is nothing to lock, it's always on. There is no "locking" on dry pavement. The system is completly transparent, even on sharp turns on dry pavement.