4x4 Auto ?

Front Runner · October 25, 2015

That's great info! Thanks for posting.

morrislee · October 26, 2015

Auto 4x4 is on demand, it is in 2wd and and when the rear wheels start slipping, TC locks up and engages the front axle. Once traction is equalized, the TC unlocks the front axle and goes back into 2wd mode.

I drive all winter in AUTO, unless I am driving on completely bare roads, which is infrequent in my locale. Lake Superior dumps a lot of snow on this part of Upper Michigan.

I am in Canada, and I live in the boonies. That snow is common here 3/4 seasons LOL

This is also my first vehicle with remote start and figuring out the 4x4 is good as I have 2WD and 4WD vehicles prior.

joefuskie · October 28, 2015

Elcamino, thanks for those information bulletins!

bendari500 · November 7, 2015

http://www.evopower.ca/mrws/filedriver/MP_Transfer_Cases.pdf

http://www.evopower.ca/mrws/filedriver/MP3023_and_3024_Operation.pdf

Links above will take you to the diagrams and explanations of how it works.

Janster · November 7, 2015

Late to the party....new to GMC's (don't own one) but not new to 4WD. I've had 4WD trucks for years and I know the systems (toyota that is).

I'm very intriqued by the Auto feature - as Toyota doesn't offer this. Please pardon these questions...(and my toy references, but that's all I know). Just trying to understand how it works based on what I'm used to.

While in 2WD, are your front axle shafts (hubs) engaged full time to the front diff ? Or is there an ADD (Auto Disconnecting Differential) system up front?

With Auto 4WD - there'd need to be full time connection everywhere. I just wasn't sure if there was another 'disconnecting/connecting' portion at the front diff between 2WD & any 4WD engagement.

When in this 4WD Auto mode...... considering it senses 'slippage' to the rear wheels and sends power to the front wheels (I get that....).

Say for instance you make a Right turn. Inside wheel has a shorter path than the outside wheel. Does the system see this as slippage?? And does it send power to the frong wheels while turning based on the physics of making a turn??

I'm in the market to buy a new truck next year. So I'm shopping around and learning....THANKS!

I totally understand Fulltime 4WD and not driving on dry pavement and not making tight turns (or the system binds up). So....I'm assuming if you're in AUTO 4WD and you make a tight turn, your CV joints are gonna still 'bind' up and especially more so - if its sending power up front.

Sorry for the questions!!

Thanks for the input!

kstruckcountry · November 7, 2015

The CV shafts are live 100% of the time, but in 2wd the front axle is not live.

I think you're confusing full time 4wd with 4lock(hi). Full time 4wd is usually used to refer to a system that operates like AWD.

In auto, the system is always sending a little power to the front. Around corners the speed difference isn't big enough to kick in the front, but a lot of times when you're turning in slick conditions the auto comes in handy to get the vehicle moving. I've never had an issue with binding. That's the main advantage, with partially cleared roads you can leave it in and not worry about binding. Another thing to think about, is that auto is variable, so it changes the output based on what it needs.

Janster · November 8, 2015

The CV shafts are live 100% of the time, but in 2wd the front axle is not live.

I think you're confusing full time 4wd with 4lock(hi). Full time 4wd is usually used to refer to a system that operates like AWD.

In auto, the system is always sending a little power to the front. Around corners the speed difference isn't big enough to kick in the front, but a lot of times when you're turning in slick conditions the auto comes in handy to get the vehicle moving. I've never had an issue with binding. That's the main advantage, with partially cleared roads you can leave it in and not worry about binding. Another thing to think about, is that auto is variable, so it changes the output based on what it needs.

Thanks!!

Ok...I think my wording is off ... the tacoma has part-time 4WD where you switch in to 4hi and/or 4lo.

Another question - with Auto 4WD, is it a mechanical system based on the 'torque' being applied (or lack of) to the viscous coupling / tcase?? Or is it electronically sensed via the wheel speed sensors that send signals to the tcase (or braking system)?

The reason why I said that is..... Toyota has an AUTO LSD (Auto LImited Slip) that's not mechanical at all. It just applies the brakes to the slipping wheel (like ABS) to equalize the power to both wheels. (I'd rather have a real LSD....lol). That's where 'my thinking' has come from.

I've had partime 4WD forever (almost) and I'm so used to just switching into 4hi anytime the roads get slick w/ snow. I guess it would be hard for my brain to comprehend putting it in Auto 4WD and trusting it'll actually be working. LOL Versus just putting it in 4WD like I always do.

Does the Auto 4WD help prevent fish tailing when the roads are just slightly wet/greasy? You know how trucks can get in 2WD - no weight on rear wheels, slight moisture on the road and making turns...... (aged tires don't help either)

Thanks again for help!! There are just certain questions / answers that you cant' get by searching google!!

kstruckcountry · November 8, 2015

The Auto is based off the front/rear wheel speed.

As soon as the rear slips under power, the front will kick in and pull it to wherever the wheels are pointed.

My understanding is that the auto system applies more power to the front at higher speeds than lower speeds. So it would help with fishtailing some. But if conditions are that sketchy I just use full 4x4.

00Silverado4x4 · November 9, 2015

The Auto is based off the front/rear wheel speed.

As soon as the rear slips under power, the front will kick in and pull it to wherever the wheels are pointed.

My understanding is that the auto system applies more power to the front at higher speeds than lower speeds. So it would help with fishtailing some. But if conditions are that sketchy I just use full 4x4.

I'll second that. I use 4 auto only to get the truck moving but if I'm in the muddy, snowy type conditions of stop and go, I'll just lock it in 4hi.

bendari500 · November 9, 2015

Disclaimer: Not a mechanic, and I love this truck.

This time of year i leave it in Auto. I noticed the benefits when going up slick wet driveways. Also when going up wet ramps in parking garage. Also when my wife is driving I have her leave it in auto mode. Wet parking garage ramps are too slick for 2WD mode (w/no weight in the rear) because traction control lights come on and the truck struggles for a few seconds, so leaving it in Auto is perfect for that situation. Especially since if i had put in 4 Hi the front end would bind as I make the corners in the parking garage prior to going up the next ramp.

In summary 4 Auto is great for wet/greasy/slick conditions or when your wife is driving. I did some tests pulling into fast moving traffic onto and from a wet roadway (left plenty of space) in 2WD, Auto and 4Hi . In 2WD the traction control lights come on as the rears spin and acceleration is poor. In Auto as the rear starts to spin it engages/disengages the clutch packs in the Transfer Case and starts transferring power up into the front wheels (this clutch engagement wasn't noticeable too me, i suspect it happens almost instantly). In 4WD HI my rear tells me the acceleration was the same as in Auto as far as I could perceive. However the front was binding as i was making the slow tight turns on wet pavement.

I "think" I can feel a little more weight in the steering wheel and heavier body motion when its in Auto mode vs 2WD. I notices this when going overspeed humps it "feels" a little different. I asked my wife and she says she couldn't tell the difference. I don't know if i'm detecting phantom motion or its just responding a little differently going over bumps.

robvas · November 9, 2015

I've had partime 4WD forever (almost) and I'm so used to just switching into 4hi anytime the roads get slick w/ snow. I guess it would be hard for my brain to comprehend putting it in Auto 4WD and trusting it'll actually be working. LOL Versus just putting it in 4WD like I always do.

Does the Auto 4WD help prevent fish tailing when the roads are just slightly wet/greasy? You know how trucks can get in 2WD - no weight on rear wheels, slight moisture on the road and making turns...... (aged tires don't help either)

Thanks again for help!! There are just certain questions / answers that you cant' get by searching google!!

Traction control and Stabilitrak also fill in a few roles with keeping your vehicle pointed straight. It's not just simply the auto-4wd system

If there's snow on the ground I usually keep the truck in auto, and if the snow is deep or really coming down (think driving in a snow storm or when there's 6" of snow out and plows didn't come out yet I just throw it in 4HI and leave it there so I don't have to wait that 1/2 second for the front wheels to kick in when I need it.

Janster · November 10, 2015

Awesome feedback gang!! THANK YOU!!!

When I bought my current truck 9 years ago.... there wasn't any/many trucks available with all those traction control devices on them (again - Toyota not offering it). The only traction control I have, is a mechanical LSD in the rear! LOL But then again, 9 years ago I wouldn't have cared and couldn't afford it.

See ...you guys are starting to really sway me. I just hope the overall size & test drive is as impressive.

kstruckcountry · November 11, 2015

Other than the Auto 4x4, my 2006 is the same way. With the locker in the rear, it's very sure footed for a near 6000 pound vehicle.

Janster · November 12, 2015

The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0-5 ft lb of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability. The NVG 246 EAU transfer case features a 4 button shift control switch located on the instrument panel. When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range position. At a single press of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp will continue to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly. During normal driving situations, the transfer case can operate in the Auto 4WD mode. In the Auto 4WD mode, the transfer case shift control module monitors rear wheel slip speed, based on the inputs from both the front and rear propshaft speed sensors. When the vehicle experiences a rear wheel slip condition, the vehicle experiences a rear wheel slip condition, the transfer case shift control module sends a pulse width modulated (PWM) signal to an electronic motor, which is the transfer case encoder motor. This motor rotates the transfer case control actuator lever shaft, applying a clutch pack. This clutch pack is designed to deliver a variable amount of torque, normally delivered to the rear wheels, and transfers it to the front wheels. Torque is ramped up to the front wheels until the front propshaft speed sensor matches that of the rear propshaft speed sensor. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again. The NVG 246 EAU transfer case has the added feature of also providing the driver with 3 manual mode/range positions:

*4HI - 4 Wheel Drive high range

*2HI - 2 Wheel Drive high range

*4LO - 4 Wheel Drive low range.

For some reason, I just now saw this. AWESOME explanation!!! I was curious whether it was 'electronic' versus 'mechanical' - and indeed, its electronic (per say). As everything seems to be going in that direction these days.

Another question - We used to own an 01 Corvette. Obviously, not 4WD....but anytime you'd get on the gas too much (QUILTY!!) and the rear wheels slipped (usually resulting in fishtailing)... the system would kill the power drastically regardless of gas pedal input.

Do these trucks operate in the same manner in ALL modes? Kills the power when too much slippage is detected?

Or - would it only do this in 2WD? - because in 4WD, you'd have less chance of fishtailing to begin with and/or power sent to the front wheels to pull you out of it? (sorry, thinking out loud)

THANK YOU for all the input gang!!

robvas · November 12, 2015

You really have to romp on it in the snow to get the truck to kick the throttle back in 4WD, but it will be all over you in the rain with 2WD. In 4WD it pretty much just pulls forward unless you're on ice.