How to Operate the 4WD?

[Marky Dissod]

For the mode switch in and out of 4HI, the truck can be rolling up to 3MpH (and rolling can help it engage smoother, although there will still be an audible clunk when it happens).

Thought it would engage more smoothly if the truck was sitting still.
Hmmm ...

 

[Fless]

Here's the Owner's Manual instructions for getting INTO 4LO:

 

[Doubeleive]

The gmc auto 4wd system isn't intended for 24/7 usage (it absolutely will cause powertrain wear); the advice above about auto 4wd reducing rear diff load is incorrect.

Here is why (generalizing)
- auto 4wd uses a clutch within the transfer case; when rear slippage occurs torque is added to the front via this clutch
- 4 hi means both front and rear axles get torque all the time, albeit at different speeds (why this is bad with high traction)

The wear during auto 4wd is because all the components are lit and getting some torque when engaged.

The reducing rear diff load comment in auto 4wd is incorrect because the rear diff gets 100% of the load until it slips before the front sheds torque. If one was in 4 hi the reduction of rear diff load would be a true statement.

if auto was "not intended for 24/7 use" it would be clearly noted as such in the owners manual, that is a statement you created out of nowhere or some misconception.
you are confusing yourself, it would be impossible to apply power to the front and not reduce power to the rear and therefore load. (there is not 2 engines with 1 that suddently kicks in to the front)
less power applied to the rear = less stress on the rear, auto does not divide power 50/50 but it will reduce stress on the rear "on demand".
yes there is a mpg hit and Divided wear (on demand) instead of 100% wear on the rear end.
that's why you can't do a burnout in auto unless you have a nice horse power upgrade, because it detects wheel spin and applies the means to correct it.
and auto is safer than 2wd, not as safe as AWD but it is a 2nd best. I will gladly take a smidge mpg hit if it might save my life and divide the wear and not put my rear end into early retirement
you could hit a pot hole in 2wd and die, but auto "might" save your life and your rear end.
I have broken several rear ends in 2wd and have YET to break one in auto or awd, why? because it splits the wear when needed = reduced rear end wear
and all those rear ends I broke were guess what? g80's guess what is on my auto vehicle and awd vehicle? that's right the exact same g80
hmm I wonder why they have not broke yet? any guess
rant over you will never ever convince me that driving in 2wd is better than auto, it's impossible.

and in reference to my first line all you will find on the owners manual regarding "auto" is this


AUTO (Automatic Four-WheelDrive) : Use when road surface traction conditions are variable.When driving in AUTO, the front axle is engaged, and the vehicle's power is sent to the front and rear wheels automatically based on driving conditions. This setting provides slightly lower fuel economy than 2wd. Do not use AUTO mode,if equipped, to park on a steep grade with poor traction such as ice,snow, mud, or gravel. In AUTO mode only the rear wheels will hold the vehicle from sliding when parked. If parking on a steep grade,use 4hi to keep all four wheels engaged.
not a single iota about not for use 24/7.......

 

[Fless]

For the mode switch in and out of 4LO, the truck can be rolling up to 3mph (and rolling can help it engage smoother, although there will still be an audible clunk when it happens). Check the owner's manual for your rig.

Corrected; I meant in and out of 4LO.

 

[strutaeng]

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://themanual.nyc3.cdn.digitaloceanspaces.com/m/car/chevrolet/chevrolet-tahoe-2005/chevrolet-tahoe-2005-owners-manual-linked.pdf&ved=2ahUKEwjksJay1-eDAxWWnWoFHWyLCBkQFnoECBMQAQ&usg=AOvVaw2hn-7lBUm9b65yShmjgmZ4

Pages 115-123

 

[Doubeleive]

Is it a preference or is there a functional reason you keep it 4 auto?

to prevent 100% wear on the rear end and it's safer than 2wd. I have broken too many rear ends in 2wd, none in auto or awd

 

[Fless]

if auto was "not intended for 24/7 use" it would be clearly noted as such in the owners manual, that is a statement you created out of nowhere or some misconception.
you are confusing yourself, it would be impossible to apply power to the front and not reduce power to the rear and therefore load. (there is not 2 engines with 1 that suddently kicks in to the front)
less power applied to the rear = less stress on the rear, auto does not divide power 50/50 but it will reduce stress on the rear "on demand".
yes there is a mpg hit and Divided wear (on demand) instead of 100% wear on the rear end.
that's why you can't do a burnout in auto unless you have a nice horse power upgrade, because it detects wheel spin and applies the means to correct it.
and auto is safer than 2wd, not as safe as AWD but it is a 2nd best. I will gladly take a smidge mpg hit if it might save my life and divide the wear and not put my rear end into early retirement
you could hit a pot hole in 2wd and die, but auto "might" save your life and your rear end.
I have broken several rear ends in 2wd and have YET to break one in auto or awd, why? because it splits the wear when needed = reduced rear end wear
and all those rear ends I broke were guess what? g80's guess what is on my auto vehicle and awd vehicle? that's right the exact same g80
hmm I wonder why they have not broke yet? any guess
rant over you will never ever convince me that driving in 2wd is better than auto, it's impossible.

and in reference to my first line all you will find on the owners manual regarding "auto" is this


AUTO (Automatic Four-WheelDrive) : Use when road surface traction conditions are variable.When driving in AUTO, the front axle is engaged, and the vehicle's power is sent to the front and rear wheels automatically based on driving conditions. This setting provides slightly lower fuel economy than 2wd. Do not use AUTO mode,if equipped, to park on a steep grade with poor traction such as ice,snow, mud, or gravel. In AUTO mode only the rear wheels will hold the vehicle from sliding when parked. If parking on a steep grade,use 4hi to keep all four wheels engaged.
not a single iota about not for use 24/7.......

In AUTO (for the 2 speed NP246e transfer case) the TC clutch packs apply a bit of power (speed) to the front propshaft; this is done to keep the propshaft spinning at the approximate correct speed for a quick engagement when needed. The front diff DOES NOT ENGAGE until rear wheel slippage is detected by the various speed sensors, and the front diff actuator is commanded to be engaged.

In AUTO there will be a short delay (normally about 1 second) when AUTO engages, due to the time it takes the front diff actuator to be commanded and fully engaged.

 

[Fless]

Thought it would engage more smoothly if the truck was sitting still.
Hmmm ...

Slowly moving parts mesh easier than stationary parts, I guess.

 

[Doubeleive]

In AUTO (for the 2 speed NP246e transfer case) the TC clutch packs apply a bit of power (speed) to the front propshaft; this is done to keep the propshaft spinning at the approximate correct speed for a quick engagement when needed. The front diff DOES NOT ENGAGE until rear wheel slippage is detected by the various speed sensors, and the front diff actuator is commanded to be engaged.

In AUTO there will be a short delay (normally about 1 second) when AUTO engages, due to the time it takes the front diff actuator to be commanded and fully engaged.

even if takes "slip" I could hit a rut in the road and loose traction on a wheel or even when making a turn this makes the outer wheel spin more.
I have never felt the auto have a Delay, It could very well be but it's undetectable to me all I ever feel is the traction control/abs kick in certain instances.

 

[Matthew Jeschke]

I didn't read all the other posts, so if somebody already posted these details I apologize. The NP246 TX case is pretty sweet. I took a couple apart (separate thread). I'm assuming that's what you have as you mentioned the auto 4wd.

It's designed to work by pressing Auto, 2hi, or 4hi while moving. A clutch pack splits the torque either 50/50 (fully engaged 4hi or 4lo) or redirects a ratio from the rear driveshaft to the front driveshaft. A little motor pulses the clutches in the case to split the torque.

The only thing, as everybody says, is you have to be careful of 4lo. Honestly, other people probably know better than I cause I've only really used 4lo a couple times. I think transmission has to be neutral... no torque to output shaft on transmission / input to tx-case. Then you can switch into 4lo. For that there's a ring gear that moves in the tx-case (if memory serves me right). There is no torque split (auto) function / locked 50/50. Otherwise everything is handled through the clutch pack.

Oh you also have a pin on a servo in the front diff to lock passenger side output shaft (lock the hub?). It's all automated though.