2 or Auto

Silverado Steve · January 13, 2017

Absolutely, straight from GM

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TJay74 · January 13, 2017

Im looking for gm documentation, found plenty of posts

Also right back at you

Why don't you post some evidence it locks the front and rear together for a 50/50 split. You haven't done exactly what your asking me to do!

Man I am very familiar with GM systems, I have worked on them for years along with working on them with my dad who retired from GM. GM does not use any sort of vectoring or torque split in their truck 4wd system, PLAIN AND SIMPLE...!!!

The only reason that while in 4Auto that the transfer case loads the clutches 10% is because it takes the transfer case actuator 10-15 seconds under a normal move from 2Hi to 4Hi. While you can shift from 2Hi to 4Hi while on the fly, if you tried to do that after reacting to a slippage event you would be 20-30 down the road before the 4Hi locked into place and you were in 4wd mode with 50/50 power split. When you go into 4Auto the actuator moves over into 4Hi with the 10% clutch hold, that way you don't have to wait on the actuator to move the hard parts over from 2Hi to 4Hi. Instead now all you wait on is the clutch pack loading to go from 10% to 100%. There is no variableness to the transfer case at all, it is either 0%, 10% or 100% engaged.

So please continue to show how ignorant you are to people who know how this system works and tell us that it works like a AWD system and we will continue to tell you that you are wrong, so please quit posting inaccurate info to confuse people who will then trust you and get into a situation that would of have normally been in had they listened to someone who knows how the actual system operates.

I have owned a 1996 Yukon 4x4, 2001 Silverado 4x4, 2010 Sierra 4x4, 2014 Sierra 4x4 and my 2016 Sierra 4x4. So to say I know how the GM 4wd system operates would be saying it lightly.

truckguy82 · January 13, 2017

Man I am very familiar with GM systems, I have worked on them for years along with working on them with my dad who retired from GM. GM does not use any sort of vectoring or torque split in their truck 4wd system, PLAIN AND SIMPLE...!!!

The only reason that while in 4Auto that the transfer case loads the clutches 10% is because it takes the transfer case actuator 10-15 seconds under a normal move from 2Hi to 4Hi. While you can shift from 2Hi to 4Hi while on the fly, if you tried to do that after reacting to a slippage event you would be 20-30 down the road before the 4Hi locked into place and you were in 4wd mode with 50/50 power split. When you go into 4Auto the actuator moves over into 4Hi with the 10% clutch hold, that way you don't have to wait on the actuator to move the hard parts over from 2Hi to 4Hi. Instead now all you wait on is the clutch pack loading to go from 10% to 100%. There is no variableness to the transfer case at all, it is either 0%, 10% or 100% engaged.

So please continue to show how ignorant you are to people who know how this system works and tell us that it works like a AWD system and we will continue to tell you that you are wrong, so please quit posting inaccurate info to confuse people who will then trust you and get into a situation that would of have normally been in had they listened to someone who knows how the actual system operates.

I have owned a 1996 Yukon 4x4, 2001 Silverado 4x4, 2010 Sierra 4x4, 2014 Sierra 4x4 and my 2016 Sierra 4x4. So to say I know how the GM 4wd system operates would be saying it lightly.

From one of our members, He says "continueally modulate pressure. "

"Gentlemen. Former Master auto tech and I have worked on the GM AutoTrac many times. It's an extremely simple system:

The transfer case uses clutches and a mechanical force motor to apply varying pressure to the clutch plates connecting to the front driveshaft.

The clutch has preload on it, which means the front driveshaft is always engaged and turning the front differential. If you go under your truck, you will find that you cannot turn your front driveshaft freely. (With enough pressure it can slip, but this would mean your clutches are probably wearing out).

So since your front diff is always spinning, it is at the correct speed when you engage 4A or 4Hi. When you shift into 4A or Hi there is an actuator on the front axle that locks the front axle to the differential carrier so the front wheels are then mechanically locked in to the power train.

The auto feature then works by monitoring input and output speed of the transfer case. It continuously adjusts pressure to the clutch pack in the transfer case to maintain no or a small percentage of slip. Because the clutch is preloaded and always has a little pressure on it, it takes milliseconds to add power to the front axle when slip is detected. This is why the system reacts so fast. You should never feel a delay in the front kicking in when in auto. If there is a delay, you have worn parts in the transfer case.

4Hi works similar, except the force (shift) motor on the transfer case simply applies high pressure at all times to the clutch not allowing any slip. There may be an actual mechanical connection in 4Hi but I can't say for sure. But I do know the clutch pack controls the auto feature.

I have seen many of these clutches burnt out from people using auto when they really should be in 4Hi and they put way too much torque on the front axle. They are clutches like in an auto transmission. Big difference is we only have 1.5 qts of autotrac fluid in the transfer case and it can get overheated quickly if the auto feature is used when conditions really warrant 4Hi. It is good to change the fluid frequently too, because of this.

Hope that helps explain a bit. Auto is meant to use for varying conditions, but if constant power is needed up front you will save your transfer case by using 4Hi. "

Silverado Steve · January 13, 2017

Alpine Sled is that you?

From one of our members, He says "continueally modulate pressure. "

"Gentlemen. Former Master auto tech and I have worked on the GM AutoTrac many times. It's an extremely simple system:

The transfer case uses clutches and a mechanical force motor to apply varying pressure to the clutch plates connecting to the front driveshaft.

The clutch has preload on it, which means the front driveshaft is always engaged and turning the front differential. If you go under your truck, you will find that you cannot turn your front driveshaft freely. (With enough pressure it can slip, but this would mean your clutches are probably wearing out).

So since your front diff is always spinning, it is at the correct speed when you engage 4A or 4Hi. When you shift into 4A or Hi there is an actuator on the front axle that locks the front axle to the differential carrier so the front wheels are then mechanically locked in to the power train.

The auto feature then works by monitoring input and output speed of the transfer case. It continuously adjusts pressure to the clutch pack in the transfer case to maintain no or a small percentage of slip. Because the clutch is preloaded and always has a little pressure on it, it takes milliseconds to add power to the front axle when slip is detected. This is why the system reacts so fast. You should never feel a delay in the front kicking in when in auto. If there is a delay, you have worn parts in the transfer case.

4Hi works similar, except the force (shift) motor on the transfer case simply applies high pressure at all times to the clutch not allowing any slip. There may be an actual mechanical connection in 4Hi but I can't say for sure. But I do know the clutch pack controls the auto feature.
I have seen many of these clutches burnt out from people using auto when they really should be in 4Hi and they put way too much torque on the front axle. They are clutches like in an auto transmission. Big difference is we only have 1.5 qts of autotrac fluid in the transfer case and it can get overheated quickly if the auto feature is used when conditions really warrant 4Hi. It is good to change the fluid frequently too, because of this.
Hope that helps explain a bit. Auto is meant to use for varying conditions, but if constant power is needed up front you will save your transfer case by using 4Hi. "

TJay74 · January 13, 2017

Here you go, not perfect but pretty good

http://m.gmc.com/gmc-life/how-to/when-to-use-four-wheel-drive.html

AUTOMATIC 4 HI

If road conditions frequently alternate between high- and low-traction areas, consider using the AUTO setting found on select GMC electronic transfer cases. This setting allows your GMC to automatically distribute torque to the front axle by anticipating the need for additional traction. Shifting into auto engages the front axle, but the transfer case sends power primarily to the rear wheels in normal conditions and the clutches modulate torque forward to provide stability and enhance traction to the vehicle. Although not always optimal for efficiency and wear of your vehicle 4wd driveline, AUTOMATIC 4 HI can be used on any road condition without risk of damaging your vehicle.

"Clutches modulate torque"

Wait a second, that sounds just like what a clutch based differential does! I'm pretty sure they didn't say "clutches lock"

Man you reading comprehension skills are severely lacking man, I have posted at least 3 times in this thread alone the transfer case while in auto mode applies the clutches 10%, then it goes to 100% when a rear wheel slippage event is detected. Once a certain amount of time is elapsed (called event decay time) then the system returns back to the normal 10% clutch loading that 4Auto uses.

AWD vehicles like Subaru and Audi (A vehicle that I also own as well so I am familiar with their system as well) have the ability to vector their power on the fly between the front and rear. Audi can apply as much as 80% of the power to the rear wheels and up to 60% to the front depending on situations, Audi can also vector side to side with their Quattro system. Subaru depends on the years, their early system put more power towards the front normally and then would either go 80/20 front to rear or 20/80 front to rear. Their newer systems are 45/55 front to rear biased and then go from there.

So as I said earlier, the GM system is nothing like a AWD system that GM uses on their other vehicles (Cadillac ATS AWD) or like any other brand that uses a AWD system.

truckguy82 · January 13, 2017

Man you reading comprehension skills are severely lacking man, I have posted at least 3 times in this thread alone the transfer case while in auto mode applies the clutches 10%, then it goes to 100% when a rear wheel slippage event is detected. Once a certain amount of time is elapsed (called event decay time) then the system returns back to the normal 10% clutch loading that 4Auto uses.

AWD vehicles like Subaru and Audi (A vehicle that I also own as well so I am familiar with their system as well) have the ability to vector their power on the fly between the front and rear. Audi can apply as much as 80% of the power to the rear wheels and up to 60% to the front depending on situations, Audi can also vector side to side with their Quattro system. Subaru depends on the years, their early system put more power towards the front normally and then would either go 80/20 front to rear or 20/80 front to rear. Their newer systems are 45/55 front to rear biased and then go from there.

So as I said earlier, the GM system is nothing like a AWD system that GM uses on their other vehicles (Cadillac ATS AWD) or like any other brand that uses a AWD system.

enough with the insults ****

If I'm wrong I'm wrong, but we have a gm master tech on here saying that the system

1)apply varying pressure to the clutch plates

2)continuously adjusts pressure

We have tjay the guy that owned a few trucks saying

"it goes from 10%-lock"

also please stop posting drivvle over and over, we are here to debate one thing, does the truck have a varying torque clutch pack or does 4auto lock the front with the rear

SouthernSilveradoGuy85 · January 13, 2017

Don't you think if it was exactly like AWD they would just call it AWD and not 4 auto? I mean that's a simple thing too realize. There are many differences and you even said it's only similar which you're trying to make the word "similar" sound like the word "exactly".

phabejhmoob · January 13, 2017

This.

The larger point here is that we all (4X4 GM owners) have a 4wd system that we can leave on all winter and only lose a mile or two per gallon, while gaining safety for ourselves and our families.

A 4wd system we can use at a boat ramp on vacation and drive home on the freeway and not have to wonder if we destroyed the transmission.

A 4wd system that engages seamlessly when our rear wheels slip if we hit an icy patch on the road

THAT is the issue, not if it's the same as a soccer mom Subaru. (nothing against Subarus, handy in the snow, but we're all full size truck drivers who likely don't consider a Subaru a substitute)

As far as I know, no other full size truck brand offers this and there is no more important feature if you live in a region that gets snow.

I make it a point to buy American, but if Toyota was the only brand selling this there would be a Tundra in the garage. The other differences between the truck brands are irrelevant.

but op is asking about "auto" mode, not 4x4. And " When in 4 Auto the system loads the transfer case clutch pack around 10%, as soon as the rear wheels detect slippage via the ABS sensor the transfer case locks in fully and splits the power 50/50 front to rear.". Subaru is all time AWD, not 10% front

Silverado Steve · January 14, 2017

This post says nothing to back your claim that in 4auto upon detection of slippage the vehicle does not act like 4hi mode. In fact in the info says, it acts like 4wd upon slippage. Do you have other info to the contrary?

From one of our members, He says "continueally modulate pressure. "

"Gentlemen. Former Master auto tech and I have worked on the GM AutoTrac many times. It's an extremely simple system:

The transfer case uses clutches and a mechanical force motor to apply varying pressure to the clutch plates connecting to the front driveshaft.

The clutch has preload on it, which means the front driveshaft is always engaged and turning the front differential. If you go under your truck, you will find that you cannot turn your front driveshaft freely. (With enough pressure it can slip, but this would mean your clutches are probably wearing out).

So since your front diff is always spinning, it is at the correct speed when you engage 4A or 4Hi. When you shift into 4A or Hi there is an actuator on the front axle that locks the front axle to the differential carrier so the front wheels are then mechanically locked in to the power train.

The auto feature then works by monitoring input and output speed of the transfer case. It continuously adjusts pressure to the clutch pack in the transfer case to maintain no or a small percentage of slip. Because the clutch is preloaded and always has a little pressure on it, it takes milliseconds to add power to the front axle when slip is detected. This is why the system reacts so fast. You should never feel a delay in the front kicking in when in auto. If there is a delay, you have worn parts in the transfer case.

4Hi works similar, except the force (shift) motor on the transfer case simply applies high pressure at all times to the clutch not allowing any slip. There may be an actual mechanical connection in 4Hi but I can't say for sure. But I do know the clutch pack controls the auto feature.

I have seen many of these clutches burnt out from people using auto when they really should be in 4Hi and they put way too much torque on the front axle. They are clutches like in an auto transmission. Big difference is we only have 1.5 qts of autotrac fluid in the transfer case and it can get overheated quickly if the auto feature is used when conditions really warrant 4Hi. It is good to change the fluid frequently too, because of this.

Hope that helps explain a bit. Auto is meant to use for varying conditions, but if constant power is needed up front you will save your transfer case by using 4Hi. "

Knotsure · January 14, 2017

I would like to have a clarification on the Auto mode on the 4X4 knob. when AUTO is selected, is it a real All Wheel Drive or the more a 4X4? Can I drive on asphalt over 60mph on dry pavement??

I would say it is more like awd than a 4x4 when in auto. You can drive on dry pavement and at any speed. That alone differentiates it from straight 4x4. I am not arguing it is like all these Subaru or Audi awd systems. Just saying I think it is more awd than an auto traditional 4x4 (if that last part makes sense).

kstruckcountry · January 14, 2017

AUTO APPLIES VARIABLE TORQUE. There.

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Silverado Steve · January 14, 2017

By variable are you saying all or none? Or like a modern all wheel drive anywhere in between 20-80, 30-70, 40-60...etc like the Honda pilot, crv and new Ridgeline does?

AUTO APPLIES VARIABLE TORQUE. There.

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kstruckcountry · January 14, 2017

By variable are you saying all or none? Or like a modern all wheel drive anywhere in between 20-80, 30-70, 40-60...etc like the Honda pilot, crv and new Ridgeline does?

Variable = 10-50%, as the computer deems neccessary.

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Silverado Steve · January 14, 2017

Where is that info. Modern awd systems can modulate anywhere between those ranges, i cant find any info, GM blods, Sandy blogs that say our trucks do that too.

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TJay74 · January 14, 2017

Where is that info. Modern awd systems can modulate anywhere between those ranges, i cant find any info, GM blods, Sandy blogs that say our trucks do that too.

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That's because you and I understand how the GM system works, it isn't a AWD variable viscous system like you see on Subaru, Audi, BMW and so on. The GM system uses a set of clutch packs that ride near the encoder motor that handles the switch from 2Hi to 4Hi. As said earlier and info that easily found on the web, the system goes ahead and switches over to 4Hi but doesn't lock the clutch pack fully so at this point the front wheels are not fully locked in. The transfer case is fully locked but the front diff and front wheels are not under power fully. Once slippage is detected (difference in speed from the front prop shaft to the rear prop shaft) the encoder motor locks the clutch pack in fully and at that point the transfer case is fully locked with equal split in power.

Viscous system use a silicone fluid and clutch packs, as a wheel slips it heats the silicone fluid up which then expands, that expansion then locks the clutch pack up fully for that axle or for the whole system.

If those guys who are saying the GM system is an AWD would just go out and do some research on the NP transfer case system that GM uses they would see and understand that the GM 4WD system does not work that way. I don't care what lingo some technician has posted, the GM system does not sit there are vary the power split in the transfer case anywhere from 0%-100%. Yes it is variable in the fact that it pre-loads the transfer case clutch, then when wheel slip is detected goes to full 100% lock up and then once slippage is no longer detected goes back to pre-load percentage.

I wish I would of had the conversation with the GM powertrain engineer over email versus the phone, I asked him about this back in 2014 to confirm what I had always thought. Even GM's own owners site pretty much says the same thing in the break down of how and when to use 2wd, 4wd and Auto.

TWO-WHEEL DRIVE

For normal operation on paved roads, four-wheel drive GMC models should be operated as two-wheel drive vehicles to save wear on the 4WD components. If road conditions are optimal or there’s no loss of traction, the “2↑” position on the transfer should be utilized. In this setting, the transmission sends power into the transfer case, which then sends power only to the rear axle and rear wheels. Although not always optimal for traction, TWO-WHEEL DRIVE can be used on any road condition without risk of damaging your vehicle.

HIGH-RANGE FOUR WHEEL DRIVE

High-range four-wheel drive, marked as “4↑” on most transfer cases, is designed for use on loose or slippery surfaces. In this setting, the front axle is engaged, and the transfer case then sends power to both the front and rear axles and to all four wheels.

This mode forces the front and rear axles to spin at the exact same speed. Due to minor tire size differences and track length differences when turning, the front and rear axles can ‘fight’ against each other on high-friction surfaces and results in a condition sometimes known as ‘crow hop’ as tires are forced to slip to the ground.

Since GMC’s transfer cases are designed to be “shifted on the fly,” drivers can shift between high-range two-wheel drive and high-range four-wheel drive without bringing the vehicle to a halt. On electronic transfer cases, an indicator on the selector knob will flash while the shift is being performed and turn solid once it’s fully engaged. For trucks equipped with a manual transfer case, an indicator within the gauge cluster will illuminate.

It’s important to note that high-range four-wheel drive is not intended to be used on dry surfaces or roads with good traction. Doing so may place undue stress on axles, transfer cases, and other drivetrain components which could lead to damage. It’s important to remember to shift out of 4 HI as soon as road conditions improve.

AUTOMATIC 4 HI

If road conditions frequently alternate between high- and low-traction areas, consider using the “AUTO” setting found on select GMC electronic transfer cases. This setting allows your GMC to automatically distribute torque to the front axle by anticipating the need for additional traction. Shifting into “auto” engages the front axle, but the transfer case sends power primarily to the rear wheels in normal conditions and the clutches modulate torque forward to provide stability and enhance traction to the vehicle. Although not always optimal for efficiency and wear of your vehicle 4wd driveline, AUTOMATIC 4 HI can be used on any road condition without risk of damaging your vehicle.

LOW-RANGE FOUR WHEEL DRIVE

GMC models equipped with a two-speed transfer case also include a four-wheel drive setting known as “low range.” Typically marked as “4 ↓”, low range effectively doubles the torque sent to the wheels, making it useful for off-road driving in deep sand, mud, or snow. 4WD Low is important for severe off-roading to allow accurate control of vehicle speed over obstacles, and to provide effective engine braking on steep grades to save the brakes from overheating. Low range is meant predominantly for off-road situations, and should not be used at speeds above 45 mph.

Shifting into low-range four-wheel drive is a little more involved than shifting into high-range four-wheel drive. Drivers will need to shift the transmission into neutral to disconnect torque to allow the transfer case to shift gears. It is sometimes helpful on Manual Shift Transfer cases to keep the vehicle moving below 3-5 mph while shifting into 4 ↓ to allow the gears to align teeth. Once the transfer case is in low-range, shift the transmission back into drive. To shift out of low-range back to high range, follow the same procedures.

It’s important to note that Low-range four-wheel drive is not intended to be used on dry surfaces or roads with good traction. Doing so may place undue stress on axles, transfer cases, and other drivetrain components which could lead to damage. It’s important to remember to shift out of 4 Low as soon as road conditions improve.