powernoodle

Hey folks. I have an '09 Suburban LT 4x4. I've never quite understood the 4x4 system, in terms of which wheels are pulling in 4x4 HI and "auto" modes.

In "auto" mode, is power going to the rear as usual, but gets diverted to one front wheel if spin is detected?

In 4x4 HI, am I getting power to one front and one rear, or how does that work, or is it at best "3 wheel drive"?

Any info is appreciated.

thx
me

73shark

Auto is two rears 'til slippage is noted then goes to 4WD.

4HI is 4WD in the high range and 4LO is 4WD in the low range.

2WD is two rears no matter what. Best for mpg. Use Auto for changing conditions such as some snow and some dry.

powernoodle

What about in 4WD HI? Am I getting power to just one front and one rear, or is it 3 wheel drive or what? I know that all 4 aren't locked up. Thats what I'm trying to wrap my brain around. Thanks.

SWHouston

If I may restate Shark's very informative reply...

Your Rear Drive is enraged Full Time, weather it's a single Wheel, or both, depends on if you have a Limited Slip/Positrack type Differential.

When you engage any 4 Wheel Mode, the Front Wheels LOCK and drive together. There is NO limited slip for cornering, and you'll hear the inside wheel "skipping" when you are turning on dry pavement. The Auto 4WD only engages the Front when the Wheel Sensors detect a difference in wheel speed. The difference between 4HI and 4LO, is a gear reduction within the Transmission allowing you considerably more Pulling Power.

The use of any 4WD function is recommended, ONLY when there are clear indications of their need.

powernoodle

So, with 4HI, both fronts are locked, and I'm getting either one or two rears, depending on if I have limited slip. Thats the info I'm after.

I bought this vehicle used. Is there a way for me to tell if I have a limited slip differential, maybe via the VIN, door sticker or other way?

I appreciate very much your responses.

SWHouston

Yes, that's correct.

You may go to this link...
http://www.decodethis.com/
enter your VIN, and then click on “Equipment” when the next page appears. It will say of either (Locking/Limited Slip) Option is available for your Vehicle, but I'm not sure if it will say if either is actually installed. One way is to lift/jack a rear wheel (just one), and see it you can turn it by hand when in Neutral.

Or, if you have a Floor Jack, come in from the Rear and lift one rear wheel. Crank it up, and put it in 2WD, slip it in gear and see if it will ease forward. If you don't have the Option installed, the lifted wheel will spin freely. Probably would be a good idea to Block the Front Wheels.

(Don't goose it though )

Just a hunch...
I'm thinking that since you have the "Auto" option, you have Limited Slip back there.

powernoodle

Well, someone else is telling me that the front doesn't lock. And I looked up the RPO code from the glove compartment, which indicates a 3.42:1 rear axle ratio. I think the code would be G80 if I had a locking or limited slip rear end.

So I think my supposed four wheel drive is really two wheel drive: one front and one rear.

What I guess I need to do is jack up the back and see for myself by rotating the wheel.

SWHouston

They could be right, I have the G80/3.73-1 as you can see below, and it locks.
Yes on the manual test, make sure, and I'd do the front as well, just to see if
there was some difference there.

73shark

If you have 4WD, then you have the G80 Eaton locking rear diff. The front is an open diff w/ no limited or locking.

If you have 2WD, then just the two rears are driving and the fronts are free wheeling.

Easy way to tell if you have 4WD is to see if you have a front diff.

SWHouston

I did a lookup on the G80 at...
Differentials & Locking Differentials

There were several different Models, Nospin, Truetrac, MLocker, Suretrac.
Couldn't find specific information to let me know which type I have though.