Looking for info on my truck

[Z71GUY]

I was wondering if there is a website out there that describes in detail exactly how our 4x4 systems work in the 99+ trucks.  I'm also curious as to how the Auto on the Autotrac system works.  

 

Thanks!

 

Eric

[CMNTMXR81]

Nope, not that I'm aware of.

 

You can see all the parts and the trobleshooting and repair chassis manuals that GM gets but they won't show you how they work.

[Z71GUY]

dang...I really wanted to know what happens in the background when I push the 4hi button and the Auto button.  Would be interesting to see the mechanics behind it...

 

 

Eric

[chevy4x4trucks]

This might be something, I know it's info on changing the axle fluid, but gives you a good schematic of your front axle

 

http://home.att.net/~m.prendergast-allieds...erado_axle.html

 

I think that w/ autotrack your front driveshaft is always engaged and when 4x4 engages it just locks the hubs or something like that.

[Shaners]

As far as the AutoTrac goes here is my theory...

 

The computer monitors the sensors on the wheels for the ABS.  When it senses the rears are moving at a different rate then the front, it engages the transfer case.  Where as 4HI leaves the transfer case engaged all the time...

[Z71GUY]

Ok, I was with Jon on this one.  I also thought in "Auto" the front shaft is engaged, but the hubs dont kick in until it detects slipage.

 

 

Oh BTW, thanks for the link.  Atleast I'll know how to change the fluid up there.

 

 

Eric

[chevy4x4trucks]

Ok, I was with Jon on this one.  I also thought in "Auto" the front shaft is engaged, but the hubs dont kick in until it detects slipage.

 

 

Oh BTW, thanks for the link.  Atleast I'll know how to change the fluid up there.

 

 

Eric

That's not a problem.

[Shaners]

I disagree.  I think the hubs lock (so obviously the shaft is turning), but the shaft is free-wheeling.  Then when slippage is noticed the transfer case will engage with the shaft.

[Z71GUY]

I disagree.  I think the hubs lock (so obviously the shaft is turning), but the shaft is free-wheeling.  Then when slippage is noticed the transfer case will engage with the shaft.

ahhh, I see what you are saying now.  That does make sense.  It would also explain the odd steering feel at slow speeds making sharp turns.  

 

 

Eric

[Smitty00Z71]

Here is the real skinny on the 99 up, includes info on Autotrack

 

http://www.4x4review.com/vehicles/chevy/99silverado.asp

[Kansas Kid]

Just out of curiosity, exactly why are you guys even mentioning hubs?  The IFS Gm 4wd trucks do not have hubs, and they never have.  Just go look at the front end of your truck sometime, and I think this would be quite obvious if you've ever looked at a real 4wd that has locking hubs.

 

Now to beginning so we can all understand exactly how the GM 4wd systems works.  The CV joints are turning when ever the truck is moving, and the front axle is enganged by CAD (center axle disconnect).  The actuator for this is now electronic compared to the old version which was thermal.  On trucks with autotrac the front axle is always engaged with when the "auto" button is pushed.   The auto transfer case has a multi-disk clutch that engages the front driveline. The clutch is similar to clutches in an automatic transmission. A PWM electric servomotor moves a clutch fork that engages the clutch.  PWM means pulse width modulated, this gives the control module precise control of the motor. This is necessary to control clutch slippage and ensure a smooth transition to four-wheel drive.  Trucks with a lever shift transfer case have a actual lever that shifts the case, no electric motor here.

 

The control module relies on output speed sensors on the front and rear output shafts of the transfer case to control the clutch engagement. It also compares the speed of the two shafts to identify slippage for automatic engagement.  There is a ton of stuff going on here and you just better hope the engineers that designed this system did a great job.

 

btw, is that in depth enough for ya?

[Shaners]

OK Kansas Kid...

 

It is much easier to say the "hubs" are engaged then go through the 1000 word essay.

 

You said what I said but you used all the exact terminology.  Thankyou for taking the time to put it all in black and white!!!

 

Shane

[Kansas Kid]

Shane, I really wish I could have done all that in less words, trust me.  That was alot of typing.  LOL  Had to do it though, as one of my pet peeves is the huge amount of misunderstanding that people on these forums have about the GM 4wd system.  Most of them don't know any better either so the bad information just keeps getting passed around.  Must just be the engineer in me, but it felt good to do that.  I guarantee that there are quite a few people here that know what their truck is actually doing now, instead of just thinking they do.

[chevy4x4trucks]

Kansas Kid (in my best bart simpson impression)  Must you always embaress me

[Z71GUY]

Just out of curiosity, exactly why are you guys even mentioning hubs?  The IFS Gm 4wd trucks do not have hubs, and they never have.  Just go look at the front end of your truck sometime, and I think this would be quite obvious if you've ever looked at a real 4wd that has locking hubs.

 

Now to beginning so we can all understand exactly how the GM 4wd systems works.  The CV joints are turning when ever the truck is moving, and the front axle is enganged by CAD (center axle disconnect).  The actuator for this is now electronic compared to the old version which was thermal.  On trucks with autotrac the front axle is always engaged with when the "auto" button is pushed.   The auto transfer case has a multi-disk clutch that engages the front driveline. The clutch is similar to clutches in an automatic transmission. A PWM electric servomotor moves a clutch fork that engages the clutch.  PWM means pulse width modulated, this gives the control module precise control of the motor. This is necessary to control clutch slippage and ensure a smooth transition to four-wheel drive.  Trucks with a lever shift transfer case have a actual lever that shifts the case, no electric motor here.

 

The control module relies on output speed sensors on the front and rear output shafts of the transfer case to control the clutch engagement. It also compares the speed of the two shafts to identify slippage for automatic engagement.  There is a ton of stuff going on here and you just better hope the engineers that designed this system did a great job.

 

btw, is that in depth enough for ya?

This is why I posted the question.  Thank you for the detailed answer.  

 

 

Eric