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4wd Auto Left On

dansk

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dansk Enthusiast

dansk

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I pulled a trailer out of my yard the other day and was worried about spinning on the grass so I clicked on the 4WD auto feature. I use it because the tires don't bind once I'm back on the driveway. Well as most of you know, that little dinky LED on the knob is not a good indicator that you are still in 4WD so I ended up towing the trailer 3 hrs with the knob on auto. Is there any problem with doing this?

DBVille Enthusiast

DBVille

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Posted

 

 

I pulled a trailer out of my yard the other day and was worried about spinning on the grass so I clicked on the 4WD auto feature. I use it because the tires don't bind once I'm back on the driveway. Well as most of you know, that little dinky LED on the knob is not a good indicator that you are still in 4WD so I ended up towing the trailer 3 hrs with the knob on auto. Is there any problem with doing this?
That is why it is not a problem. The open center "diff". No problem, except 0.2 mpg loss or whatever.
dansk Enthusiast

dansk

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Thanks, that is what I thought and a good reason to use the auto feature since I'm prone to forgetting to shut it off. Man, if anyone came out with a means to have something on the guage cluster light up when out of 2WD, I'd be all over that mod for sure.

07max Enthusiast

07max

Posted
Posted
Are hubs new for 09? Can you put manual hubs in now?

 

Auto engages the front drive shaft via the transfer case but does not lock the front 1/2 shafts @ the diff. The computer waits to sense wheel spin, which will then engage the front diff. The front 1/2 shafts are always spinning. In 2WD mode the tcase disengages the front drive shaft. I've done the exact same thing. I liked the OBS 4x4 button cluster high on the dash. It was easier to tell what "mode" the 4x4 system is in.

 

-Steve

2COR517 Enthusiast

2COR517

Posted
Posted

Thought I would clarify how the auto four wheel drive function works in these trucks. Just to clarify, the front "Axle" is made up of a center differential section, with a central axle disconnect (CAD) motor on the right extension housing. Equal length CV, or "Half-shafts" connect the wheels to the diff housing. There are no unlockable hubs at the wheels. The CV shafts are constantly rotating with the tire, similar to a front wheel drive vehicle. The transfer case contains clutches that are used to control the front driveshaft.

 

When in 2wd, the transfer case is driving the driveshaft. This means your front driveshaft is turning all the time, regardless of what button you push on the dash. This is necessary to allow immediate engagement of the CAD when a 4 wheel drive mode is selected. When you choose Auto4wd, two things happen. The CAD motor engages the front axle, then the transfer case clutches release. The clutches are engaged as the PCM senses wheel slip. This process is controlled up to fifty times per second. When you choose 4Hi or 4Lo, the CAD of course engages, and the transfer case clutches are fully applied. Because of the clutches in the transfer case, you must use GMs Auto Trac fluid only in your Tcase.

VMax2007 Senior Enthusiast

VMax2007

Posted
Posted
Thought I would clarify how the auto four wheel drive function works in these trucks. Just to clarify, the front "Axle" is made up of a center differential section, with a central axle disconnect (CAD) motor on the right extension housing. Equal length CV, or "Half-shafts" connect the wheels to the diff housing. There are no unlockable hubs at the wheels. The CV shafts are constantly rotating with the tire, similar to a front wheel drive vehicle. The transfer case contains clutches that are used to control the front driveshaft.

 

When in 2wd, the transfer case is driving the driveshaft. This means your front driveshaft is turning all the time, regardless of what button you push on the dash. This is necessary to allow immediate engagement of the CAD when a 4 wheel drive mode is selected. When you choose Auto4wd, two things happen. The CAD motor engages the front axle, then the transfer case clutches release. The clutches are engaged as the PCM senses wheel slip. This process is controlled up to fifty times per second. When you choose 4Hi or 4Lo, the CAD of course engages, and the transfer case clutches are fully applied. Because of the clutches in the transfer case, you must use GMs Auto Trac fluid only in your Tcase.

 

 

Best explanation EVAR! :D

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