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4WD Auto

Questions about using 4wd

4WD Auto

Postby swervin36 [OP] » Jan 27 2011, 3:18am

I live in NE Pa and drive 55 miles one way to work. I work in the Poconos. With the weather we have been having I often leave the truck in Auto instead of 4-HI so I can get a little better MPG. My question is am I hurting anything by running my truck this way. Also if I put my truck in 4-HI how far can I drive it and at what speeds before risking damage to the transfer case? Thanks for the help guys...
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Re: 4WD Auto

Postby EKinMN » Jan 27 2011, 3:26am

Using Auto 4wd will not hurt anything. It is there and available if the truck detects wheel slippage. But, the hubs are free, so it's not putting extra load on your transfer case.
You don't want to use 4wd high for long distances on dry pavement.
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Re: 4WD Auto

Postby Austin » Jan 27 2011, 3:28am

I don't imagine it hurts a thing to leave it in 4WD-Auto. I'm also confused as to why leaving it in 4-HI would have a limit to how far you can drive and what speeds. Why would it? Since when is using your trucks capabilities risking damage?
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Re: 4WD Auto

Postby EKinMN » Jan 27 2011, 1:36pm

Using 4 hi is fine in a straight line. But as you turn, the wheels turn at different speeds into the corners. Since everything is "hooked together" and trying to turn at the same time, it puts additional strain on the drivetrain. That may show up as tire wear, or early component failure in the drivetrain.
On snowy or icy surfaces, 4wd high is just fine anytime. The tires can then slip ever so slightly on the road surface to compensate for the rotational differences in the wheels.
I use 4wd auto the most. I only go to 4wd high when I know I am going through some seriously deep snow, or if I am going off road.
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Re: 4WD Auto

Postby Hartski » Jan 27 2011, 2:00pm

I leave mine in auto unless it's snowing pretty good or it's icy. In the summer, I put it in 2wd
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Re: 4WD Auto

Postby lzn197 » Jan 27 2011, 2:29pm

When you shift to auto 4 wheel drive, your front axle is engaged so all of the components of your front axle are turning as you drive (front shafts, driveshaft ETC). The transfer case DOES apply a very slight (maybe 5%) rotational force (torque) through an internal clutch to the front driveshaft and because the front axle is engaged, it is ready and waiting for a "slipping event" from the rear axle. When the vehicle senses a difference in speed from the rear axle to the front (rear wheel slip), the clutch within the transfer case applies MORE torque to the front driveshaft to make the front and rear axle turn at the same speed. Kinda like a slightly slipping 4 wheel drive. If the vehicle continues to see a speed differential from the front and the rear axles, the clutch within the transfer case continues to add more torque and eventually will be locked in. As the wheel slip goes away, the transfer case returns to the 5% mode and waits for the next slip event. When you put the vehicle in 4 HI, the front axle is engaged and it receives 100% torque through the internal clutch within the transfer case. A good practice I have found is to NEVER put it in 4 HI on dry pavement. Even if you are going straight!!!! I hope this helps. I believe we have a user on here that works for one of the transfer case manufacturers. Maybe he can give more details. My facts are based on my 2004 Silverado. I assume vehicles today with the same transfer case operate the same way. I hope this helps and as always, READ YOUR OWNERS MANUAL!
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Re: 4WD Auto

Postby jepics » Jan 27 2011, 3:18pm

Thanks for the great info, Gordon. I was pretty sure I didn't want to use the AUTO 4WD function, and you've given me the facts to support my assumption.

I prefer to set it into 4WD when I need it, and be sure I return it to 2WD when I'm done. Based on your explanation, there's a long-term cost associated with the AUTO setting, and since I plan to have my truck a long while, I will continue to give it the best care possible, and avoid expensive repairs later.
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Re: 4WD Auto

Postby bradneal » Jan 27 2011, 3:31pm

Pretty much what's already been said, but here's what the owners manual from my 2010 Sierra says:

AUTO (Automatic Four-Wheel Drive) : This setting is ideal for use when road surface traction conditions are variable. When driving the vehicle in AUTO, the front axle is engaged, but the vehicle's power is sent only to the front and rear wheels automatically based on driving conditions. Driving in this mode results in slightly lower fuel economy than Two-Wheel-Drive High.

Notice: Driving on clean, dry pavement in four-wheel drive for an extended period of time can cause premature wear on the vehicle's powertrain. Do not drive on clean, dry pavement in Four-Wheel Drive for extended periods of time.
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Re: 4WD Auto

Postby koolz71 » Jan 27 2011, 3:34pm

Thanx gordon i was actually going to reply to what u were saying..my brother is an ASE tech and i actually asked him this question a month ago and got the same response. he told me stories of soccer moms who would leave it on all the time in the rain, and anytime they felt unsafe and that they would come in with transmission issues due to this. Thanx for the great info.
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Re: 4WD Auto

Postby bradneal » Jan 27 2011, 3:42pm

jepics wrote:Thanks for the great info, Gordon. I was pretty sure I didn't want to use the AUTO 4WD function, and you've given me the facts to support my assumption.


Just as a point of clarification, there is nothing wrong with using Auto 4WD. It won't damage the vehicle and only engages when necessarily. Not that you would want to leave it on all the time, but if you are driving on roads with patches of ice or snow, then by all means, use it. Probably the biggest downside to using the Auto mode, is the hit that you take on the MPG's.
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