2 or Auto

[KA0S]

Yeah if the roads are black there's no need for auto

 

 

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But is it effectively prematurely wearing it out if it is used in Auto all the time?

[Sierra706]

 

But is it effectively prematurely wearing it out if it is used in Auto all the time?

effectively

 

 

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Yes

 

 

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[Luster]

No, 4wd Auto is not the same as All Wheel Drive. With All Wheel Drive power is applied to all 4 wheels all the time in most systems. I believe Subaru's AWD systems work differently, but the concept applies. With 4wd Auto, the front hubs are locked and when there is wheel slippage detected, power is then applied to the front diff. In a All Wheel Drive system, there is a center diff that adjust toque to the wheels that keeps driveshaft binding from happening. A standard 4wd system doesn't have this and this is why you will feel wheel hop when turning the steering wheel in 4wd on dry pavement. There are many posts on this topic, if you want to read more in depth, try doing a search on "4wd" or "All Wheel Drive" It was discussed way in depth here a few months back.

 

Agree 100%.

[Black Denali Canada]

All I know is, I can't do fantastic burn outs with it in auto, so I switched it to 2wd and let that 6.2L howl !!! Ha ha ha ha

 

 

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[chrisuns]

Ehh, a lot of mis-information here. Fwiw, GM uses a Magna-Steyr 3023 in the Silverado/Sierra. It is a selectable system between Active AWD, part-time 4WD, 2HI, 4LO and neutral - this is straight from the manufacture of the transfer-case - Magna. It's also known internally to them as the Ultimax chain drive 2-speed active transfer case. During 4auto the torque is modulated by a software which they call "Diff-Mimic active torque control", it varies torque based off wheel slip, steering angle and throttle input - according to their literature (which is a bit in layman's terms in comparison to how the system is actually programmed).

During 4auto operation, the TCCM reads data from the bus like: wheel speed sensors,vehicle speed, brake pressure, yaw rate sensor, steer wheel position sensor, any information relating to stabilitrak or traction control activation and throttle % from my memory. From there it compiles that data to determine torque bias rates. A variable bias from about 98%R/2%F to 50%R/50%F. So any regards to saying the system shoots to 50:50 anytime there is slip is incorrect - First off, that would be incredibly harsh on several mechanical parts and induce more NVH to the passengers (think dropping a clutch in a manual car); second off, the motors used to activate the clutches would overheat (they can consume anywhere from 17-24 amps from what I've personally measured on 100% activation and they're not designed to shed that heat load rapidly). Also, the system is way more preemptive than you think. If you give it 100% throttle from a stop, you can watch the TCCM command the encoder motor to start modulating torque before there's any sign of discernible traction loss - Granted, I have to the tools at my disposal to watch the data.

Personally, I don't see what the huge argument is here? It is a selectable system that has AWD as one of it's functions, it's way more advanced than using a mechanical means of differentiating like the Silverado SS (it doesn't use viscous coupler that requires traction loss to heat silicone to start working, nor does it require brake biasing from the EBCM like the older denali/escalades) . Heck, most AWD cars now use an electronic or electro-hydro means to control a biasing clutch unit: BMW, Cadillac, Nissan GT-R etc., mechanical differentiating is antiquated in a transfer case to be frank and rare in new production cars. Then you can lock it in 4x4 (100% clutch activation and the motor brake is on) for off-road etc and have 4low...

Now, why didn't GM label it AWD, no idea. I would imagine that they want to reduce the chances of customers running in AWD 100% of the time for warranty claims. The 3023 is used in certain Jeeps; however, that unit is only AWD,4H, 4LO and N, but it also allows the driver to select different biasing profiles: snow, sport, off-road, etc. They do have a few minor internal differences in the form of bearings, one of which is part of the clutch system which I know GM uses a lower quality bearing - which could be one of the reasons.

Fwiw, I also have a custom NP246 autotrak that I have in my duramax which has around 1k FT.LBS. of torque and weighs 8200 pounds. I have a ton of miles on the case, it lives in 4auto and I floor that thing multiple times a day. So I have a bit of experience with these systems as I've taken them all apart and even done data bus hacking to modify crap for the hell of it.

[Black Denali Canada]

Within the menu GM does call it AWD, I agree that they would prefer the truck to be driven in 2WD for multiple reasons (such as fuel economy) and labeling the switch AWD would just cause people to leave it there exclusively.

 

Thank you for the detailed and informed write up BTW!

 

 

 

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[Knotsure]

Ehh, a lot of mis-information here. Fwiw, GM uses a Magna-Steyr 3023 in the Silverado/Sierra. It is a selectable system between Active AWD, part-time 4WD, 2HI, 4LO and neutral - this is straight from the manufacture of the transfer-case - Magna. It's also know internally to them as the Ultimax chain drive 2-speed active transfer case. During 4auto the torque is modulated by a software which they call "Diff-Mimic active torque control", it varies torque based off wheel slip, steering angle and throttle input - according to their literature (which is a bit in layman's terms in comparison to how the system is actually programmed).

During 4auto operation, the TCCM reads data from the bus like: wheel speed sensors,vehicle speed, brake pressure, yaw rate sensor, steer wheel position sensor, any information relating to stabilitrak or traction control activation and throttle % from my memory. From there it compiles that data to determine torque bias rates. A variable bias from about 98%R/2%F to 50%R/50%F. So any regards to saying the system shoots to 50:50 anytime there is slip is incorrect - First off, that would be incredibly harsh on several mechanical parts and induce more NVH to the passengers (think dropping a clutch in a manual car); second off, the motors used to activate the clutches would overheat (they can consume anywhere from 17-24 amps from what I've personally measured on 100% activation and they're not designed to shed that heat load rapidly). Also, the system is way more preemptive than you think. If you give it 100% throttle from a stop, you can watch the TCCM command the encoder motor to start modulating torque before there's any sign of discernible traction loss - Granted, I have to the tools at my disposal to watch the data.

 

Personally, I don't see what the huge argument is here? It is a selectable system that has AWD as one of it's functions, it's way more advanced than using a mechanical means of differentiating like the Silverado SS (it doesn't use viscous coupler that requires traction loss to heat silicone to start working, nor does it require brake biasing from the EBCM like the older denali/escalades) . Heck, most AWD cars now use an electronic or electro-hydro means to control a biasing clutch unit: BMW, Cadillac, Nissan GT-R etc., mechanical differentiating is antiquated in a transfer case to be frank and rare in new production cars. Then you can lock it in 4x4 (100% clutch activation and the motor brake is on) for off-road etc and have 4low...

 

Now, why didn't GM label it AWD, no idea. I would imagine that they want to reduce the chances of customers running in AWD 100% of the time for warranty claims. The 3023 is used in certain Jeeps; however, that unit is only AWD,4H, 4LO and N, but it also allows the driver to select different biasing profiles: snow, sport, off-road, etc. They do have a few minor internal differences in the form of bearings, one of which is part of the clutch system which I know GM uses a lower quality bearing - which could be one of the reasons.

 

Fwiw, I also have a custom NP246 autotrak that I have in my duramax which has around 1k FT.LBS. of torque and weighs 8200 pounds. I have a ton of miles on the case, it lives in 4auto and I floor that thing multiple times a day. So I have a bit of experience with these systems as I've taken them all apart and even done data bus hacking to modify crap for the hell of it.

Not a lot to argue with in this post. It sounds like you have good first hand experience. Thank you for taking the time to write that up.

 

 

2014 Chevy silverado Z71 DCSB w/Bilstein 5100 level