A4WD on dry pavement

[Frankd1]

I just realized that my wife has been driving with the selector set to A4WD on dry pavement for several hundred miles....
Is this something that would cause damage or wear and tear? I realize that driving in 4HI on dry pavement is a no no because of the potential for damage but I wasn't sure about A4WD.....
My understanding is that in A4WD the front is on "alert" in the event of rear wheel slippage but otherwise will not engage unless the rear wheel slips..

 

[Sparky]

Probably didn't hurt it, although the "on alert" mode does put like a 5% torque bias to the front IIRC. No really enough to likely do anything, but over a long period of time could cause increased wear over time.

Stick it in 4HI and try to do a low speed tight turn. Does it want to bind and crow hop? Then you're fine, stick it back in 2HI and move on

 

[Mooseman]

Putting it in A4WD puts it in the same mode as the AWD only trucks like the Bravada, Rainier and 9-7x. Basically, the front disconnect is "on" and keeps the front wheels connected to the differential. When the TCCM detects rear wheel spin, it shifts the transfer case to 4x4 temporarily and then after a while, shifts it back to 2WD however still leaving the front wheels connected. I call it the "slip/bang" system.

Leaving it in A4WD won't hurt anything except MPG a little and adding just a tiny little bit of wear to the front system. In fact, a lot of people leave it in A4WD "just in case" not realizing this. It would be most useful driving on snowy roads as it would engage only when needed. Personally, I'd just put it in 4HI then. My 9-7x is basically permanently in that mode and I hate it with its slip/bang effect.

 

[BRomanJr]

Since GM started with the A4WD Transfer case and the Blue fluid (around 2000), the Front axle drive Clutch in the Transfer Case utilizes a residual friction (5% ???) at all times.

This means that all parts spin no matter what, what is locked varies. The fact that everything always spins allow for the non-destructive normal driving and the on-the-fly engagement feature. This on-the-fly feature means (if the system is working properly) you can change into or out of any mode except 4LO or Neutral while moving at any speed.

Examples:
When is 2HI, the Disconnect is open and the Clutch has only residual friction, but everything spins when driving. No front drive is provided.

When in A4WD the disconnect is locked (mimics the Bravada, and others with non-selectable A4WD), the clutch has residual friction and can slip on turns. The system monitors slippage and the clutch will be engaged when needed and all wheels drive for a period of time until the front to rear slippage is eliminated. This could translate to a front ~5% ?? bias when in this mode (like Sparky noted above).

When in 4HI or 4LO, the Disconnect is locked and the TC Clutch is locked, normal 4WD operation, not for dry roads of course.

 

[linneje]

I have had my 2003 for about 8 years now, and I have always used A4WD if the traction is "iffy" in the winter, including on the highway if the highway is "iffy". Never had a problem with the transfer case or differential. MPG is a little worse, but would rather have more control.

If the highways here are good in the winter (about half the time) I drive in 2HI.

 

[Frankd1]

Thanks guys!
Yeah I've always instructed her to use 4HI and only when the road conditions warrant ie, slippery roads in deep snow etc and then to switch back to 2HI again.
For whatever reason during the last snow fall, she must have switched to A4WD and then forgot to switch back to 2HI, so I figure its been driven 400 miles or so on dry pavement but sounds like no harm done.

I noticed it last night on the highway so I switched back to 2HI on the fly.

I haven't checked the system by trying to get it to bind and crow hop in 4HI in a slow tight turn, but I'll try that with the next snowfall..

What I do generally do is to cycle the switch between the various modes while in park and listen for the correct sounds from underneath, and also that the indicator light does what it is supposed to do - flash while selection is occurring and then solid once selection is set.

With snow on the roads in 2HI, I gently apply gas to break the rear end loose and get the fish tail, then select 4HI and do the same but no rear end fish tail.....tells me the front end is engaged.

Oh, and I did notice about a 2mpg difference when I filled the tank!