AWD vs 4WD

[JustinH]

Hummers are all-wheel drive, right? I'm trying to figure out the difference between AWD and 4-wheel drive. What would be the advantage to put the transfer case in 4-HI if I already have power going to both axles and the traction control is in effect either way?

Justin

[cgalpha08]

They are full time 4 wheel drive, which is different than awd, although im not sure what the difference is

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[Hunner]

Actually, it is my understanding that from info from other sources and this sticker under the hood, it is ALL WHEEL drive.
I believe it is a 60 rear 40 front ratio in 4 Hi and shifting to 4 lock makes it 50/50.

[cgalpha08]

Yep my bad, hunner you are right.

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[Mark]

I have seen this debate played out a number of times and it is normally the none Hummer owners that say it's All Wheel Drive while the more knowledgable people claiming it is Four Wheel Drive, not sure who is right. I personally don't know what makes the difference but I could see that sticker being less about what it actually is and more about CYA from GM so that anybody reading it knows you can not put it in two wheel drive unlike most four wheel drive vehicles. Anybody know what actually makes the difference? Hunner is correct in that 4HI is 60/40 split while either HI or LO locked is a 50/50 split.

[cgalpha08]

I researched this some, and the only difference i could find was that AWD is more or less automatic, where as the 4WD has a selectable hi lo feature.

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[Mark]

Don't all wheel drive systems tend to move the power around a bit more depending on conditions and type of driving (performance) unlike on the H3 were it is either 60/40 or 50/50.

[cgalpha08]

Don't all wheel drive systems tend to move the power around a bit more depending on conditions and type of driving (performance) unlike on the H3 were it is either 60/40 or 50/50.

I believe so, i think it responds to wheel spin and shifts the power around where it is needed.

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[JustinH]

... Hunner is correct in that 4HI is 60/40 split while either HI or LO locked is a 50/50 split.

Well, I guess this is the important part for my understanding. Thanks!

[ltr450crbm]

AWD is the new marketing term for 4wd cars that are not intended to go off road.
AWD is 4WD and vice versa.
Here in Australia we call AWD cars "soft-roaders".
As opposed to 4WD cars being "off-roaders".
Subaru WRX or Liberty (Legacy) are also AWD, with not intention whatsoever of going off road. The AWD is for safe handling.
AWD may be used to denote constant 4WD, as Hummers are. We can not disconnect the front drive.
4HI is just a constant 4WD with all diffs open. Any split in torque front-rear would only be relevant on bitumen. In extremely slippery conditions the car would become only a 1WD = one wheel drive, as torque finds the path of least resistance.
4HI locked means that the centre diff is locked => torque is always split 50% front and 50% rear. With front and rear diffs open, in extremely slippery conditions the car becomes a 2WD (one of the front wheels and one of the rear wheels).
4Lo is same as 4Hi , only the ratio of transfer case changes.
4Lo Locked + rear diff lock turns the car into a 3WD.
4Lo Locked + rear locker + front locker finally gives you a true 4WD ! Where all 4 wheels always get driven.
Wonder if anybody will bother reading this ?
Cheers

[f5fstop]

You want the true SAE meaning as set forward in J2008 back when I was the GM representative to the SAE board? (Now understand this could have changed in the last few years since I left government motors.)

AWD does not have a selectable low range tranfer case (however, I believe in the past few years, there have been some AWD systems released that do have a selectable t/case).
Full-time 4-wheel drive has a selectable t/case.

AWD will transfer power as needed between the normally driven wheel without driver input (most are done via electronic solenoids, some are done via clutch slippage) and the other axle; most full-time 4x4 systems keep at a set power to the axles.

As for that sticker under the hood, that is a generic GM warning sticker and is appropriate for any awd or 4 wheel drive system that is mounted to a 2 wheel drive dyno. In other words, don't stand in front of the vehicle when it launches itself from the dyno. It was not used to determine the type of drive system it was used to protect human body parts.

In GM engineering, the Hummer line was considered to be a full time, 4x4 system. And yes, we did have a few selectable models running around for testing to see how much fuel mileage would be increased with a selectable 4x4 system (similar to the Heep). And guess what, without lockout hubs, the difference in fuel mileage as negligible so the system remained a full-time system.