Racing in AUTO vs 4X4
 

Read this from another page and it got me thinking.

When you shift to auto 4 wheel drive, your front axle is engaged so all of the components of your front axle are turning as you drive (front shafts, driveshaft ETC). The transfer case DOES apply a very slight (maybe 5%) rotational force (torque) through an internal clutch to the front driveshaft and because the front axle is engaged, it is ready and waiting for a "slipping event" from the rear axle. When the vehicle senses a difference in speed from the rear axle to the front (rear wheel slip), the clutch within the transfer case applies MORE torque to the front driveshaft to make the front and rear axle turn at the same speed. Kinda like a slightly slipping 4 wheel drive. If the vehicle continues to see a speed differential from the front and the rear axles, the clutch within the transfer case continues to add more torque and eventually will be locked in. As the wheel slip goes away, the transfer case returns to the 5% mode and waits for the next slip event. When you put the vehicle in 4 HI, the front axle is engaged and it receives 100% torque through the internal clutch within the transfer case. A good practice I have found is to NEVER put it in 4 HI on dry pavement. Even if you are going straight!!!! I hope this helps. I believe we have a user on here that works for one of the transfer case manufacturers. Maybe he can give more details. My facts are based on my 2004 Silverado. I assume vehicles today with the same transfer case operate the same way. I hope this helps and as always, READ YOUR OWNERS MANUAL!

Has any one done back to back testing between AUTO and 4x4 with the new trucks. ( are these diff than nnbs transfer cases)

If not, I could come spring. In a higher hp truck, id think leaving it in 4x4 would be a better choice but for us ~400 wheel guys, maybe the auto will get us a couple mph on the top end?

A few guys have posted they launch in 4wd and turn it off right after the 1-2 shift. They say they run a tenth or so faster than leaving it in 4wd

What you gain on the top end from auto would likely be lost on the launch waiting for the controls to detect the inevitable slip and apply torque to the front axle. If you launch in 4wd and try shifting out, you're rolling the dice with your transfer case whether or not it wants to yank the synchro assembly out of the front hub to complete the shift or just break the aluminum shift fork attempting it.

Agreed and I've also always thought it was a bad plan to make the transfer case apply or release under WOT but it's not my truck.

Choda for results on what it does at the track Gorske has posted quite a bit about it and his other testing if you read through his posts.

I used to do it all the time on my 07 4wd to 2wd after the 1-2 and it definitely improved et but I remember Atomic saying same as smokeshow. It's a gamble. I also used to nail it at 40-50 without downshifting the 4l60 and blow the tires off until auto trac kicked in just because it was fun. Not a great idea either lol. Actually pretty freaking stupid.

I race my truck now going from 4x4 to 2wd after the 2nd gear shift. Ill have to play with it come spring. I was hoping someone has tested the AUTO function.

Oh I see your point. As I recall it did let go and go back to 2wd in auto trac when it would stay hooked but I seem to also recall others saying on previous models to mine (07) they would stay engaged in all 4.

The auto deal is good rolling or if you ease into it but under a hard launch it bangs in hard. I tried that 4HI to 2wd while racing years ago and it did speed up a tenth and half and 2mph but ended up killing the shift fork, and drum, I quit doing it after that.