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Discussion Starter #1 (Edited)
As winter has firmly cast its spell here in the Northeast, I've been leaving my truck in 4WD auto all the time. There's a decent chance I may hit ice/snow/slush at some point during my daily driving, and I don't want to be caught without 4WD if I suddenly need it.

My impression is that the 4WD auto operates like 2WD unless the system detects wheel slippage, then it kicks into 4WD. Any harm in leaving the system in 4WD indefinitely? Is there a negative effect on fuel mileage?

I've tried to glean this info from the transfer case threads, but I'm not sure I fully understand the mechanism. Thanks!
 

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I'm not sure about negative ramifications, but I'm not so sure you need to be so paranoid about slush or ice. I don't need 4wd unless it's deep. Drove home tonight in about 2" of snow in 2wd and did just fine. If anything, it helps keep you in touch with true road conditions.
 

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I don't leave mine in 4WD Auto all the time, but if conditions warrant I have no issue leaving it there for days if not weeks in row. I had a 2010 Ram 1500 Hemi company truck that I simply left in 4WD Auto all winter long when the truck was assigned to me, after all it's a company truck and everyone knows you don't even have to check the oil on a company truck! Anyway, that truck is still in our fleet driven by one of my employees going strong with about 100,000 miles on it now and never a problem with the transfer case or front end.
 

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I tend to leave it engaged. All depends on the conditions you drive through. There will be a slight drop in fuel economy. I turn it off if I'm in a dry parking lot, or I need to rapidly change direction on a snow covered road.
 

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No problem with leaving it in 4 auto. You can use it in the middle of summer if you want. About a mile per gallon hit to the mileage.
 

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The owner's manual says there is a reduction in fuel mileage because the front axle shafts are turning even if the transfer case is sending no power to the front wheels. I would also thingk the front drive shaft is also turning. When in 2wd these items are not rotating. Other than mileage no harm
 

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I personally use 2WD all the time unless the roads are covers with snow/hard packed snow as in you can't see the pavement (they don't plow here).

If its snowing heavy, freezing rain, ice, or contently driving on packed snow I use 4WD auto. I must stress, if I see pavement I use 2WD, as in any black road.

Only in deeper snow and mud do I use 4WD Lock.


I also run winter tires and primarily drive on road. You're mileage may very.
 

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The owner's manual says there is a reduction in fuel mileage because the front axle shafts are turning even if the transfer case is sending no power to the front wheels. I would also thingk the front drive shaft is also turning. When in 2wd these items are not rotating. Other than mileage no harm
The front axle shafts are always turning regardless of 2wd or 4wd. They are attached to the front wheels via constant velocity joints that do not ever disconnect.
 

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The front axle shafts are always turning regardless of 2wd or 4wd. They are attached to the front wheels via constant velocity joints that do not ever disconnect.
SHNNGNS-I am trying to understand what is happening in the shift between 2 wd and 4wd auto. AS I read your post you seem to be saying that when in 2wd the complete front drivetrain, including axles, differential and front driveshaft is turning and the only thing happening is the fancy clutch in the transfer case is engaging and disengaging. Is that correct? What puzzles me is that the following is a direct copy from the owners manual disk for the 4wd system equipped with 4wd auto.

This electronically shifted transfer case is designed to be driven in the two–wheel drive position (2WD) or four - wheel drive position (4WD AUTO) for normal street and highway conditions on dry hard surfaced roads). Driving the vehicle in 2WD will have greater fuel economy benefits as the front axle is not engaged in 2WD.

For variable driving conditions, the 4WD AUTO mode can be used. In this mode, the front axle is engaged, but the vehicle's power is sent to the rear wheels. Four - wheel drive will be automatically engaged when the vehicle senses a loss of traction. Because the front axle is engaged, this mode will result in lower fuel economy than the 2WD mode.

While it does not directly say that the front axle is disengaged when in two wheel drive it specifically says the front axle is engaged when in 4wd auto, implying it wouldn't be engaged in 2wd.

ANy enlightenment on this would be appreciated.
 

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I don't claim to know it all, but I do know that the front half shafts that run from the wheels to the differential do not disconnect from the wheels. Whether the driveshaft from the transfer case to the front axle stays connected on the axle side I do not know. Based on how the manual reads I would think it does not, but the manual isn't always right. I'm hoping someone that has dug deeper than I has more in depth input.
 

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I don't claim to know it all, but I do know that the front half shafts that run from the wheels to the differential do not disconnect from the wheels. Whether the driveshaft from the transfer case to the front axle stays connected on the axle side I do not know. Based on how the manual reads I would think it does not, but the manual isn't always right. I'm hoping someone that has dug deeper than I has more in depth input.
Well at least we are both in the same boat, 'not knowing it all.':) I hope someone that does 'know it all' on this issue wil take the time to enlighten us all. I would really like to understand this. GENE(Anomaly) you usually seem to have access to a good book with schematics on it. Do you have something that can enlighten us?

All the best,
 

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Discussion Starter #12
Thanks for the responses everyone. I read the portion of the owners manual that mentioned a decrease in fuel economy in 4WD auto, but I'm still not sure why that would be the case. Seems that when on dry roads, the 4WD would function similar to 2WD, as better explained by the other posters in this thread.

Those who mentioned that all-the-time 4WD auto is overkill, you're probably right. I'm coming from an AWD SUV, and never had to think about when to engage 4WD. Except in deep snow when I'd put it in 4 wheel "lock."
 

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Discussion Starter #13
Also, thanks to all for pointing out that there's no harm to leaving it in 4WD auto, other than fuel mileage concerns. Puts my mind at ease.
 

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Thanks for the responses everyone. I read the portion of the owners manual that mentioned a decrease in fuel economy in 4WD auto, but I'm still not sure why that would be the case. Seems that when on dry roads, the 4WD would function similar to 2WD, as better explained by the other posters in this thread.

Those who mentioned that all-the-time 4WD auto is overkill, you're probably right. I'm coming from an AWD SUV, and never had to think about when to engage 4WD. Except in deep snow when I'd put it in 4 wheel "lock."
In any 4wd mode the actuator in the front axle engages. This ties the right and left axle shafts together. When that happens the front ring and pinion starts spinning and that causes the front driveshaft to start spinning. All of that causes a drop in fuel economy because it takes energy to move all of that stuff.

http://en.m.wikipedia.org/wiki/Center_axle_disconnect
It isn't exactly the same but the same principles apply.
 

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In any 4wd mode the actuator in the front axle engages. This ties the right and left axle shafts together. When that happens the front ring and pinion starts spinning and that causes the front driveshaft to start spinning. All of that causes a drop in fuel economy because it takes energy to move all of that stuff.

Center axle disconnect - Wikipedia, the free encyclopedia
It isn't exactly the same but the same principles apply.
Thank you. That is the answer I was looking for and it makes perfect sense and agrees in principle with the owner's manual too.
 

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Everything I'm reading about the center axle disconnect related to heavy duties with solid front axle. I'm not sold on this theory.
 

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Screenshot_2015-01-31-21-43-51.png
Everything I'm reading about the center axle disconnect related to heavy duties with solid front axle. I'm not sold on this theory.
Part number 6.
You looking up the wrong term. It isn't called that on all axles. The term central axle disconnect is the one dodge chose back in the 90's.
 

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Discussion Starter #19
Thanks for the diagram and wikipedia link loveracing1988 - I think I get it now. This forum is great!
 
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