on the 99-07 classic trucks, there is an option on the 4x4 selector to run Auto 4WD - What is the differnce for this? I usually run 2-Hi until I ...

on the 99-07 classic trucks, there is an option on the 4x4 selector to run "Auto 4WD" - What is the differnce for this? I usually run 2-Hi until I feel the rear wheels slipping, and then put it in 4-Hi. My question is - what actually is "Auto 4WD"?

Auto 4wd is just a way to have the truck be able to use 4wd when needed, but not have it in 4wd all the time. It's a waste in my opinion and I never found the need for it.

But how it works is that there are clutches in the transfer case. When you select auto 4wd, the front axle engages and the clutches slightly preload. When there is wheel slippage, thebtranfer case fully engages the clutches and sends power to the already engaged front axle until the slip is no longer happening.

GMs intended use in the manual days something to the effect of mixed traction surfaces. So for example a road that has some snow on it, but also is clear in some areas.

That makes a lot of sense. I usually opt for 4-hi just for when my wheels start to spin, but I might try out the auto function.

We just got about 10 inches of snow here in MN and they are awful about plowing the streets. I might just use that on bad roads where it looks clear but is also snowy in spots.

YouTube has several videos with visual explanations as to what it does.


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I will sometimes select Auto 4WD when it's raining. Maybe not so much now since I got new tires, but with the old set I could barely start moving if I was on an incline and had to stop. It was a constant battle between spinning and traction control taking over.

Jetmech76 wrote:I will sometimes select Auto 4WD when it's raining. Maybe not so much now since I got new tires, but with the old set I could barely start moving if I was on an incline and had to stop. It was a constant battle between spinning and traction control taking over.

Same here - I used to do this in the winter or heavy downpours with my stock Goodyear LS2s but since getting K02s the truck feels more planted. I haven’t used Auto 4wd since.

Since winter is here, I throw a couple hundred pounds of sand in the bed and good to go. Rather keep it in 2wd unless I absolutely need 4 wheels going.


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Same here. If in a heavy downpour I switch on the AUTO, especially when it first starts to rain. The rain starts to wash off all the oil and crap from the vehicles, making the road a little slicker than normal at first. It's great in snow as well, when the asphalt peaks through, and then disappears underneath the snow.

AUTOMATIC TRANSFER CASES
The last category is a combination of 4WD and On Demand AWD. These transfer cases have a 2HI, Auto-4WD, 4HI, 4LO and Neutral position and would fall in the general 4WD category. This transfer case has the operating characteristics of both an On Demand AWD and a Part-Time 4WD system depending on the mode selected. This transfer case uses a clutch pack to allow for a difference in speed between the front and rear axles in the Auto-4WD mode. In the 4HI or 4LO modes, there is no allowance for the difference in speed between the front and rear axles.

I love auto. I like using it with intermittent slippery roads in the winter. Especially trailering. If the roads are pure snow or ice I usually go 4 hi.
I never use 4 lo.

I've never used the auto 4x4 function. Use 4-hi when I need 4x4. About the only times I use 4-lo is when I wish to creep really slow on a primitive road or when I need to get unstuck when 4-hi failed.