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dumb qestion..diff between 4x4 &AWD?

lordvette

Full Member
Joined
Mar 14, 2005
Messages
400
i cant seem to get a clear answer on this one and it started when my family member asked me the diff between my "Avy" and a "Escalade".what is "AWD" and why it doesnt make it a good off road vehicle and why cant a 4x4 be drivin on dry street pavement ??? hope this is the right place for this question ??? if not sorry :(
 
lordvette said:
i cant seem to get a clear answer on this one and it started when my family member asked me the diff between my "Avy" and a "Escalade".what is "AWD" and why it doesnt make it a good off road vehicle and why cant a 4x4 be drivin on dry street pavement ??? hope this is the right place for this question ??? if not sorry :(

I believe it is AUTO 4wd. means the front wheels are not engaged unless the rears lose traction
 
Typically 4WD or 4x4 is a mechanical system involving the transfer case, front differential & front hubs & delivering a more locked up system than AWD, hence the reason that it shouldn't be driven on dry pavement (front wheels don't turn at the same rate as the rear so they push / pull the rear around).

AWD systems typically have some smarts involved too (a computer controlling which wheels get power). As one wheel gains / looses grip, the system will redistribute torque to the other wheels. This setup is constantly changing as you drive. I have never seen an AWD system that delivers a fully locked 4wd in addition to AWD.

All that said, with the various traction management systems being added to these trucks, the lines between the two systems are becoming pretty tough to define. I've wondered if the Auto4 system in our Avs is really just an AWD function. One key piece of that system is the encoder motor & sensor. If that part isn't working correctly (which is not uncommon, is it?), then the Auto4 system doesn't engage & disengage correctly as traction changes. Since we've been driving snow packed roads the last month or so, I have felt my own Auto4 system NOT disengaging correctly as the truck is getting good traction....... you can feel the truck start to "hunt" as your driving, steering gets a bit stiffer, etc.

No clue how Cadillac's system works. Or what about the Denali?
 
First of all...there are no "dumb" questions.

Now, the difference between 4wd and AWD...

 AWD is exactly that.  All 4 wheels turn at the same speed with the same gear ratios all the time.  4wd doesn't have to have the same front/rear gear ratios and running it on pavement will lead to excessive tire ware promptly followed by transfer case failure and possible tranny issues.  Newer cars use what is called smart all wheel drive (variations on wording depend on manufacturer).  Basically, a front wheel drive vehicle with a computer that senses when one or more of the 4 wheels is spinning at a radically different speed from the rest, and sends power to the appropriate wheel/wheels to compensate for the difference...sort of a variation on Corvette's active handling feature where it applies the brakes to a specified wheel during hard, hi-speed cornering to allow for better and more controlled handling.  The Avalanche's "auto" feature on the 4wd keeps it in rear wheel only mode until the computer senses a radically different speed between wheels and then applies power to the front wheels until it senses that all is under control again, then reverts back to rear wheel only drive.  The computer will sense these changes and react much more quickly than a human.  Usually by the time we realize we have a wheel slipping, we have been slipping for quite some time and are teatering on out-of-control.

In my opinion...that was a very good question.
 
All wheel drive from Cadillac site

Full-time All-Wheel Drive with single-speed open differential transfer case.

So it's like ms38w said
 
MichiganSilver03 said:
All wheel drive from Cadillac site

Full-time All-Wheel Drive with single-speed open differential transfer case.

So it's like m38w said

Sounds like the Caddy has matched gears...........
 
MichiganSilver03 said:
All wheel drive from Cadillac site

Full-time All-Wheel Drive with single-speed open differential transfer case.

So it's like ms38w said

I love it when people agree with me.

Will you be my friend? :cool:
 
So the Caddie system has only a high range (single speed). What does it mean that it's "open"?

And does that differ from a conventional 4wd system?
 
Yeah I had to go to the Cadillac site, I didn't know it was a single speed, that would explain why it's not good off road.
 
Yes the the transfer case is different.
 
MichiganSilver03, help me out here...

I believe this means that the Caddy lacks things like "4hi" and "4lo"...it simply is 4wd all the time with the front gears being of equal ratios to the rear gears.  I also believe that you can't choose to go rear wheelin' only...it is always spinning all 4 wheels at the same speed, requiring no input from the driver?? Or is it rear wheel until the computer senses the slippage and then goes into all wheel with no input from the driver?
 
Yep one speed, by open I believe its more like a differential in operation if one set of wheel slips it engages the other.
 
ms38w said:
MichiganSilver03, help me out here...

I believe this means that the Caddy lacks things like "4hi" and "4lo"...it simply is 4wd all the time with the front gears being of equal ratios to the rear gears.  I also believe that you can't choose to go rear wheelin' only...it is always spinning all 4 wheels at the same speed, requiring no input from the driver?? Or is it rear wheel until the computer senses the slippage and then goes into all wheel with no input from the driver?

Depends on if it's a Full time symmetric AWD (all 4 wheels have power) or Full time assymmetric AWD system (2 wheels have power & 2 get power as needed). Different vehicles use different systems.

Lots of info here:  http://www.4x4abc.com/4WD101/4WD-AWD-autoAWD.html
 
I read a little more about it, there is a 60/40 split of torque and drive is applied to all wheels all the time and it uses the stability system to apply brakes to the tire with less traction.

And thats all the reading I'm doing tonight.
 
MichiganSilver03 said:
I read a little more about it, there is a 60/40 split of torque and drive is applied to all wheels all the time and it uses the stability system to apply brakes to the tire with less traction.

And thats all the reading I'm doing tonight.

very similar to Corvette's active handling then...minus the addition of power to wheels...
 
MichiganSilver03 said:
I read a little more about it, there is a 60/40 split of torque and drive is applied to all wheels all the time and it uses the stability system to apply brakes to the tire with less traction.

And thats all the reading I'm doing tonight.

That would be the symetric system described on that site, similar to Mercedes M class, most Subarus, & the Audi Quattro. 
 
Yep I imagine the system would handle much better than the AV with the constant drive to all wheels, but not good at all offroad. I assume it would heat up quickly and shut off.
 
I actually had a similar discussion with LordAries (are we allowed to speak his name??).  I still think that, if you don't use the 4wd for off-road, it would be pretty cool on the Av, and probably not too difficult of a mod, to apply the Caddy stuff.
 
Sperry, may he rest in peace, posted an excellent and very specific General Motors authored description of the differences between the mechanical and operating characteristics of GM's two catagories AWD systems and three catagories of 4WD systems.

His post was dated February 19, 2005.  I don't have the link, because I am referring to a printed version of the post which truncated the url on the bottom, as it was quite long.  The title to the post was "RPO NP8 Transfer Case 101."  Although NP8 refers to the Auto 4WD transfer case found in 2500 AVs, the document that Sperry postes is actually a service document offering a review of all of GM's AWD and 4WD systems, prepared by GM for GM technicianss who had the same question as you did... what is the difference.  The post is 5 full pages long, and it explains, in detail, the differences in GM's systems.

Not sure where on CAFcNA this post is located, but you might start with the Sperry forum.  Otherwise, note the date  2/19/05.

Sperry was great.  He took a great deal of time to find and post the details of how these trucks work.  I miss him.   He was the only reason why I found/joined this site.
 
Yeah sperry was a bowl full of knowledge about this thing, probably how I caught the mod bug starting with the LUX System.


But to answer the heating up question off road wheel slip the transfer case does not transfer power it tries to brake the wheel with no traction something is bound to heat up
 
Yep, I somehow got notice that you sent a PM.  Check out my signature though.  It seems that after over 2 years of membership and over 40 posts that clearly demonstrate an abiding and longer term interest in contributing to the forum on subjects related to the Av... there still appears to be some perception of risk that I might spam you and everyone else with a flood of unrelated PMs,  if only given the opportunity.  I don't have pm access.  I've brought the issue up before, when I first learned about it, and encounterd a sand pit.  So I am unable to read PMs, or PM you back.

But I did find the thread I mentioned.... http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,41895.0.html

Now I'll have to follow your link to see if it points to the same thread!

On edit, just checked.  Bingo, same thread.  You beat me to it Air Junky.

On whatever your encoder motor sensor question was, if you find one of the three threads on Service 4WD that I posted on, in deepest detail, in the spirit of Sperry, and re post your PM on that thread, then I will eventually find it via the "Responses" tab, and will do my best to answer, to the extent my limited experience permits, any question you might have. 
 
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