This is going to be a pretty stupid question I am sure, but this is my first four wheel drive vehicle in my life.

I'm looking basically for some detailed info on really how many wheels actually drive?

I know with a traditional car, and a regular differential, only one wheel actually drives the car-I know both wheels can have power applied, but the way the differential works, the one with the least traction gets the most power, rendering the other wheel useless if you get stuck in the mud.

Now with 4 wheel drive trucks, I know that engaging 4x4 locks the transfer case, so you should have at least power going to one front wheel and one back...

I guess the question lies in the differentials on these things....not even sure how to ask it properly LOL.

FWIW, I have the "limited slip differential". I bought the truck from dealer stock-If I had been picking options to have one built I probably would have opted for the ELD option.

So basically, are these "posi" [i know-gm term) or "trak-loc" diffs front and back or no.....?

Thanks,

-Alan

 

the limited slip is only in the back...

so right now you have one front wheel with power and the other dont

the rear you have two unless the difference of traction is really big....

it is a "limited slip" so it limit the amount of one wheel drive

so you have 3 wheels with power unless there is to much traction difference between both rear wheels

 

I'm not sure that it is very obvious what exactly you're asking because you appear to answer your own post but anyway.

If both ends were open diffs then it would technically be 2wd in a zero traction situation.

With the *clutch based* LS diff in our trucks, in a "low" traction situation, you may see as much as 3wd be it only temporary. There are several variables with this situation though: how different the traction may be between the surfaces under the left and right rear tires, how much torque you are asking to be transmitted through the differential with your right foot, as well as wether or not you have left your traction control on. With the LS diff the traction control can often force the torque to the wheel with more traction by individually applying the brakes to the spinning wheel making the other wheel appear, from the perspective of the differential, as being the path of least resistance for the torque.

Wikipedia has some great write ups on the differences of the different 4wd and awd systems. The article about Audi's quattro is a good place to start.

Also, the common term for your limited slip rear is just that, limited slip. If I remember correctly, true "posi" refers to the Detroit "truetrac" helical gear limited slips that were used in later GM muscle cars. The term "posi" does seem to have been popularized to refer to any vehicle that will "two wheel peel", if only occasionally.

Truetrac LS is a little bit of a bear to explain for me so let's just say it's more proactive than reactive like a clutch based LS or GM's G80 auto-locker concerning the way it vectors torque.

The biggest problem with the G80 from GM is that the wheel has to slip (like a lot) for the locker to engage. In my expearience its not what I would call "subtle", and it usually just leads to both wheels spinning. Also, they have a propensity to buy the farm if you use them often.

 

Yeah, I was not very good at wording my post. I guess I posted how I *thought* it worked, and was looking for confirmation or correction. This is my first 4x4 I have ever owned or even driven for that matter.

Either way, your two posts gave me exactly what I was looking for.

One thing that threw me, I own 2 mustangs, and believe the window sticker indicated "trak loc" difs when I bought my 06 at least. My truck said "limited slip". I did not realize the two were the same thing until now.

Thanks,

-Alan

 

This is the way I have always 'understood' this aspect of the typical 4X4 system. In fact, this is a very important option to me, and why I never buy one of these vehicles (SUV or PU) without the limited slip rearend on the window sticker equipment options list.

I think many people, who may not have owned a 4X4, just naturally assume that a 4X4 means, motive traction on all four wheels, when in that mode of operation.

When you purchase a non-limited slip 4X4 vehicle, you only have motive power to one front and one rear wheel, when in four wheel drive mode; therefore, in some situations, it may be easy to get stuck in snow or mud, even if it says 4X4 on the side of the truck.

Also, what is nice about limited slip, is that even in two wheel drive mode, you still have traction to both rear wheels, which many times is enough to get you out of a sticky spot, without shifting into four wheel drive.

 

No problem Alan. Like I said wikipedia has some great articles on the stuff... Not all 4WD and AWD cars are created equal.