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Today I had the first opportunity to appreciate the sure-footed 4WD on my 14 Sierra in some slow speed (under 20 MPH) situations. Came to a complete stop at the base of a hill that a number of cars simply could not make it up. Once it was my turn to go, I put it in 4WD High and effortlessly rolled to the top of the hill, then shifted out.

Later, nearing my parking lot, I was on almost 100 percent ice and was losing speed with 2WD due to rear wheel slippage so I shifted it back to 4WD until I made the parking lot. Once again, I was impressed by the immediate return of full control.

I realize there is an Auto setting. Wanted to get some feedback from other owners as to how these two settings compare in normal winter driving and which setting some prefer.
 

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4WD is for slippery conditions ONLY, if used on clear roads your tires will wear quickly and your handling will suffer to the point of being dangerous
AUTO mode goes between 2WD and 4WD automatically using clutches and the front axle is already connected so you will have a MINOR loss of FE in "summer" conditions and NOT loose any handling in dry conditions and it will almost instantly become 4WD when wheel slippage happens

MY 07 is in AUTO and will stay there until the snow gets deep or goes away (in 6+ months)
 

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Leave it in auto. The greatest thing about auto is that your wheels will not bind up when your on drier ground, you save fuel, and you don't have to worry about getting into or out of 4wd when it's needed. When it gets really nasty, use the 4WD.
 

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Nobody should be tooling around in "Auto" 365 days a year unless you enjoy wasting gas and rebuilding your transfer case every few years. The transfer case is not designed for continuous Auto or 4 wheel drive usage. Believe your manual states this.

You should leave it in 2High all the time especially on dry surfaces. In a rainy situation where you need max acceleration from a stand-still, such as pulling out onto a busy wet road for example, "Auto" can be useful. In auto mode, the transfer case is engaged but power isn't applied to the front wheels until there is slippage detected in the rear wheels. But you're still pushing all of the machinery in the transfer case in Auto mode-- all the time. This can wear on internal components in the transfer case and reduce fuel economy somewhat.

Switch to 4High on road only if there is an accumulation of snow or ice and you need extra traction all the time--or off road in sand, gravel, mud, deep snow, etc.

Switch to 4Low in deep sand, mud, climbing or descending hills, pulling a boat up a ramp, dragging a car out of a ditch or other times when the torque multiplication of the low gear range will assist.
 

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This is how I used the 4x4 system:

2hi - normal dry conditions. on road
auto - slick street, rain, light snow
4hi - offroad, heavy snow on street
4lo - offroad, low speed.

Do not leave it in auto all the time. This is a waste of fuel and adds unneeded wear to the 4 wheel drive system.
 
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Leave it in auto. The greatest thing about auto is that your wheels will not bind up when your on drier ground, you save fuel, and you don't have to worry about getting into or out of 4wd when it's needed. When it gets really nasty, use the 4WD.
I have had more "Scary situations" in "Auto Mode" than in 4x4 Hi mode. Now that is from 25 years of driving in Full 4x4 mode on Slippery Roads.

Full 4x4 Mode, I know to Accelerate through a corner, Never let off on the throttle, I know what to expect, and what is coming. Just gradually apply throttle and accelerate through an icy corner. I proved this to 1 of our Techs in a 1995 GMC K1500 with 2 Bald tires on a naughty/icy Highway one night.

Now Auto Trac, I have had it engage while the back end was starting to get loose. "MY" first instinct was to let off of the gas, which suddenly causes a 4 wheel slide. Even before I know it, both axles want to turn at the same speed.

I know I am not an Expert Driver. But I have driven 1000's of miles when No one should be on the Road. "4x4 IS YOUR FRIEND" When the road is Snow Packed and Covered.

When the Road has "May Have Icy Spots (i.e. Shade covered Corners) And Driving is "Some Icy Sections". Turn a bend to find Black Ice, I would go with Auto Trac. With the knowledge that Auto Trac, may correct me at anytime! Other than that, I run in 4x4. And let Stability Control do the work.
 

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So in "auto," the front wheels are turning the front diff, which is turning the front driveshaft, and the transfer case engages, sending power to the front driveshaft when slip is detected?

Seems like GM should have came up with a 2WD/AWD/4hi/4low transfer case like in some Dodge products, or a fixed-AWD/4hi/4low transfer case like in my Durango
 

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Thanks for the responses. I assume the locking rear differential will engage, if necessary, in 2Hi, 4Hi, OR Auto, right?
The Eaton G80 locking rear diff that GM uses (when option is checked or standard with tow package/Z71 I believe) works independent of the 4x4 system. It is a mechanically engaged locker (not driver selectable electronically or vacuum) that engages in certain situations when one rear wheel loses traction (under a certain speed--I think 20mph) and locks both rear wheels together. If you spin the low traction wheel too fast, it will not engage.

Go to youtube and search on "Eaton G80" and you can see how it works. If you search on "twist ditch" you can also see some cool videos of the trucks in action.

Some people hate them but they are fine for most on-road situations and light off roading. They aren't made to handle rock crawling or other extreme off roading.

Next time it's raining or with light snow on the road, you should experiment with light acceleration runs to get a feel for how the rear end engages on your truck. You can hear/feel it lock in if you listen carefully.
 

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What he said. I didn't make myself clear. Of coarse, I don't use auto during the summer. I also live in the North. We have snow and ice covered roads from October until May.
 

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So in "auto," the front wheels are turning the front diff, which is turning the front driveshaft, and the transfer case engages, sending power to the front driveshaft when slip is detected?

Seems like GM should have came up with a 2WD/AWD/4hi/4low transfer case like in some Dodge products, or a fixed-AWD/4hi/4low transfer case like in my Durango
The transfer case is like that? In 1500 trucks. It has 2hi, 4hi, 4lo and auto modes. The front axle locks and the transfer case controls the power sent to the front axle via a clutch set and torque sensor. In lower speed turning it transmitts 0-5ft lbs of torque to allow the front end to not crow hop (bind).
 

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Rear axle sounds like the standard mechanical posi-traction that's been on HP cars for decades.

2WD unless you're stuck. 4wd gives a false sense of security IMO.
You will dig four deeper holes instead of two shallower holes. I've had a 6x6 Army deuce and a half stuck in snow and it took another one to snatch it out with one Big Momma chain. Glad that chain didn't snap! :eek:
 

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Let me rephrase, 2wd unless you're in DEEP SNOW or on a beach. 4LO is good until 45mph on the Colorado apparently, lol. Says to only use it in deep snow or in sand though.

So I guess 2wd until your tires can no longer accelerate, then some type of 4auto/4HI.

Rear axle sounds like the standard mechanical posi-traction that's been on HP cars for decades.



You will dig four deeper holes instead of two shallower holes. I've had a 6x6 Army deuce and a half stuck in snow and it took another one to snatch it out with one Big Momma chain. Glad that chain didn't snap! :eek:
That must have been fun.
 

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The transfer case is like that? In 1500 trucks. It has 2hi, 4hi, 4lo and auto modes. The front axle locks and the transfer case controls the power sent to the front axle via a clutch set and torque sensor. In lower speed turning it transmitts 0-5ft lbs of torque to allow the front end to not crow hop (bind).
ok yeah, definitely a different transfer case. The '98 Durango had the 2WD, the 4WD "full time," 4WD "part time," and 4WD Low. The "full time" was a 50/50 full time split with a viscous coupling like in my Forester allowing for some give like when turning on pavement. 4WD "part time" and low are the conventional "locked" by gears engaging kind of 4WD. This transfer case had a lever.

The '05 Durango just doesn't have the 2WD option (rotary dash switch). It's permanently AWD (full time) with a 50/50 torque split, then "4LOCK" and "4LO." There's a little button that you need a pin or paper clip to press for neutral.

When driving in light/medium snow I like having "full time" AWD but having a 2WD option is nice...AWD isn't going to help much when like driving on a paved road in a desert and its 100+ degrees out. You can argue that there's extra driveline and tire wear (must keep properly rotated) plus some fuel economy loss but oh well.

The "auto" modes in trucks sound basically like having a truck with manual locking hubs, but driving with them locked, and the PCM engaging the transfer case into 4WD right when the ABS sensors detect slip. I guess that's not all bad but
 

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I'm on my 4th Silverado with full time 4WD, never use 4Hi and 4Low.

I use Auto all the time though. Pulling the boat out of lakes in the summer, and the nice thing there is if you leave it in Auto it does not matter. It only engages when the rear wheels slip, so the usual dry pavement warnings of 4Hi/4Low don't apply.

I use Auto a LOT in the winter. My dad leaves it in Auto all winter. I turn it off when roads are dry, but a lot of the time in Wisconsin you don't really know when you come across snow or ice on country roads, so it's on a lot.

Agree with the other guy on people driving like normal because they have 4wd, you still need to match speed to conditions and be more careful any time there are treacherous conditions. I would not leave it in 2wd though- Auto 4wd is a safety feature and a big reason to own a GM truck.

Ford/RAM are starting to put it in their trucks more, but it's on ALL GM trucks and I don't think that is the case with the others. (or even close)
 
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