Auto 4x4

pronstar · November 30, 2018

1. No, it doesn’t work like that.

Auto 4 does not engage and disengage 4wd so there is no use for an indicator.

It is a constantly variable system that adjusts power to the front. It’s nearly identical in function to a traditional awd system, and you would never drive an awd vehicle and wonder if the awd is activated

Traditional AWD functionally uses a center differential...so I’m not sure how these are identical in function to the equipment in our trucks?

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Ravenkeeper · November 30, 2018

Owners Manual P.270-272, "Automatic Transfer Case"

"2^ (Two-Wheel Drive High) : Use for driving on most streets and highways. The front axle is not engaged. This setting provides the best fuel economy.

AUTO (Automatic Four-Wheel Drive) : 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 2^.

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 4^ to keep all four wheels engaged."

Now I want to go to AV Chevy and see how many of their 4x4s are in AUTO, as opposed to being in 2^, like the manual says.

Edited November 30, 2018 by Ravenkeeper

truckguy82 · November 30, 2018

1 hour ago, pronstar said:

Traditional AWD functionally uses a center differential...so I’m not sure how these are identical in function to the equipment in our trucks?

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Our clutch based transfer case is identical in function to a center differential. Many modern awd systems use a clutch based center diff, infact most do. Many of them are also far lower quality than the ones in our trucks. Many of them can’t even distribute 50/50 power split between the front and rear.

I don’t think many gm truck owners realize how awesome the system is. You literally have 3 selectable drivetrains. Not many vehicles can have all the benefits of 4wd, 2wd, and awd. Not only is it fantastic it function, it just so happens to be extremely reliable and holds up to a lot of abuse.

The only thing we are missing for perfection is a locker on the front axle.

pronstar · November 30, 2018

Our clutch based transfer case is identical in function to a center differential. Many modern awd systems use a clutch based center diff, infact most do. Many of them are also far lower quality than the ones in our trucks. Many of them can’t even distribute 50/50 power split between the front and rear.

I don’t think many gm truck owners realize how awesome the system is. You literally have 3 selectable drivetrains. Not many vehicles can have all the benefits of 4wd, 2wd, and awd. Not only is it fantastic it function, it just so happens to be extremely reliable and holds up to a lot of abuse.

The only thing we are missing for perfection is a locker on the front axle.

Is a clutch-based transfer case really considered a center diff?

On-demand AWD and true AWD (all wheels driven all the time) aren’t functionally the same...?

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AllterrainX440 · November 30, 2018

10 hours ago, truckguy82 said:

Our clutch based transfer case is identical in function to a center differential. Many modern awd systems use a clutch based center diff, infact most do. Many of them are also far lower quality than the ones in our trucks. Many of them can’t even distribute 50/50 power split between the front and rear.

I don’t think many gm truck owners realize how awesome the system is. You literally have 3 selectable drivetrains. Not many vehicles can have all the benefits of 4wd, 2wd, and awd. Not only is it fantastic it function, it just so happens to be extremely reliable and holds up to a lot of abuse.

The only thing we are missing for perfection is a locker on the front axle.

Any idea what the power split ratio is on our trucks in auto?

A few years ago I sat through a BMW presentation on x drive and how they were the only suv awd system that could independently send 100% of the power to a single tire. Pretty cool demonstration on how none of the other awd systems could figure out how to power out of a traction loss with 3 of the 4 wheels out. I wonder how our trucks awd stacks up

https://www.youtube.com/watch?v=U-FoUTPja4Y

truckguy82 · November 30, 2018

8 hours ago, pronstar said:

Is a clutch-based transfer case really considered a center diff?

On-demand AWD and true AWD (all wheels driven all the time) aren’t functionally the same...?

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If we didn’t have the option of 4hi and 4lo they would call it a center diff.

Awd is simply using 3 diffs, one center, one front, one back. We have all 3. Some diffs are gears, some are clutch. (There are some exceptions, such as acura sh-awd which does not use a center diff)

Traditional 4wd has no center diff and just locks the front and rear together. Because our system does not lock the front and rear together in 4auto, and it constantly adjusts power to the front, it operates just like a center diff, thus making it awd by definition.

Take my wifes awd rdx for example (not sh-awd)

-front diff - open

-rear diff - open

-center diff - clutch based that transmits up to 30% power to the rear wheels if it detects slippage in the front.

Our sytem in 4auto setting

- front diff - open

-rear diff - locking diff

- center diff - clutch based that transmits up to 50% power to the front wheels if it detects slippage

truckguy82 · November 30, 2018

12 minutes ago, AllterrainX440 said:

Any idea what the power split ratio is on our trucks in auto?

A few years ago I sat through a BMW presentation on x drive and how they were the only suv awd system that could independently send 100% of the power to a single tire. Pretty cool demonstration on how none of the other awd systems could figure out how to power out of a traction loss with 3 of the 4 wheels out. I wonder how our trucks awd stacks up

https://www.youtube.com/watch?v=U-FoUTPja4Y

4auto power range to front tires = 5-50%

A system that can send 100% power to one tire primiarly is used for on-road performance. It’s just happens to be good for off-road as well.

As far as getting unstuck or getting up an incline, nothing is better than just locking all the diffs together. When our system is sending 50% power to the front, it is effectively locked at the center diff.

The only reason you wouldn’t use 4auto in very bad conditions is because; why would you heat up the clutches when you have the ability to put it in 4hi and just mechanically lock the center diff.

aseibel · November 30, 2018

On 11/28/2018 at 11:51 AM, AllterrainX440 said:

Two questions in regard to the auto 4wd

1. Is there any way to tell when the truck switches to 4wd while in auto?

yes, when your rear end breaks loose, and then it doesn't and you start moving, that's when it kicked in the front axle.

So many people talking about AWD. That's not how this works, as far as I know when you select 4auto, the truck is still sending ALL the power to the rear axle UNLESS a slip is detected, then the clutch grabs the front driveshaft to make instantaneous 4wd. I don't know how long it continues to engage the front, but I don't think its long after you reach speed. If your rear end is not slipping, you are just driving in 2wd, with the front driveshaft being spun by the road turning your front wheels.

This is why its pointless to use 4auto unless the road is snow or ice covered or maybe in heavy rain.

truckguy82 · November 30, 2018

2 hours ago, aseibel said:

yes, when your rear end breaks loose, and then it doesn't and you start moving, that's when it kicked in the front axle.

So many people talking about AWD. That's not how this works, as far as I know when you select 4auto, the truck is still sending ALL the power to the rear axle UNLESS a slip is detected, then the clutch grabs the front driveshaft to make instantaneous 4wd. I don't know how long it continues to engage the front, but I don't think its long after you reach speed. If your rear end is not slipping, you are just driving in 2wd, with the front driveshaft being spun by the road turning your front wheels.

This is why its pointless to use 4auto unless the road is snow or ice covered or maybe in heavy rain.

No, it does not do that.

it constantly changes the power to the front. It’s not just a simple automatic on and off clutch grab.

That is exactly how many awd systems work

also it is not sending all the power to the rear in 4auto, it is sending 5% to the front at a minimum and 50% as a maximum. So if you turn on auto 4 and you have perfect rear wheel traction, it’s still sending 5% of the power to the front

that is why it is completely fine to use auto4 in any condition you want

in fact the only condition you dont want to use it is in heavy snow, because you might as well lock it in 4hi and not force the clutch to constantly work

Edited November 30, 2018 by truckguy82

aseibel · November 30, 2018

17 minutes ago, truckguy82 said:

No, it does not do that.

it constantly changes the power to the front. It’s not just a simple automatic on and off clutch grab.

That is exactly how many awd systems work

also it is not sending all the power to the rear in 4auto, it is sending 5% to the front at a minimum and 50% as a maximum. So if you turn on auto 4 and you have perfect rear wheel traction, it’s still sending 5% of the power to the front

that is why it is completely fine to use auto4 in any condition you want

in fact the only condition you dont want to use it is in heavy snow, because you might as well lock it in 4hi and not force the clutch to constantly work

Well that is news to me that it is a variable system. I thought it was all or nothing. I just found another post on an older thread where somebody stated that in 4auto, the clutches are loaded to 10% when no slippage occurs (who know how much power is transferred to the front at 10% of clutch grab, you said 5%, that could be true). That's fine, but again, this is why I won't use it on clear pavement, even if wet. I don't want to be in 10% 4WD all the time. If the roads are so bad that I need 4 powered wheels, I put it in 4HI. Wet pavement doesn't create enough slippage for me to drive in 4WD.

truckguy82 · November 30, 2018

8 minutes ago, aseibel said:

Well that is news to me that it is a variable system. I thought it was all or nothing. I just found another post on an older thread where somebody stated that in 4auto, the clutches are loaded to 10% when no slippage occurs (who know how much power is transferred to the front at 10% of clutch grab, you said 5%, that could be true). That's fine, but again, this is why I won't use it on clear pavement, even if wet. I don't want to be in 10% 4WD all the time. If the roads are so bad that I need 4 powered wheels, I put it in 4HI. Wet pavement doesn't create enough slippage for me to drive in 4WD.

You don’t have to, but it’s perfectly fine if you do.

Keep in mind 5% or 10%, it doesn’t matter, the important part is that the front axle is not locked to the rear axle, which is the only reason you can’t drive around in 4hi on a dry street.

ftwhite · December 2, 2018

On 11/30/2018 at 9:25 AM, aseibel said:

Well that is news to me that it is a variable system. I thought it was all or nothing. I just found another post on an older thread where somebody stated that in 4auto, the clutches are loaded to 10% when no slippage occurs (who know how much power is transferred to the front at 10% of clutch grab, you said 5%, that could be true). That's fine, but again, this is why I won't use it on clear pavement, even if wet. I don't want to be in 10% 4WD all the time. If the roads are so bad that I need 4 powered wheels, I put it in 4HI. Wet pavement doesn't create enough slippage for me to drive in 4WD.

You must have sticky-er rain in Green Bay, or better roads. Here in the northwest, we have crumbling roads, and even light rain brings out the oils on the roads and creates traction challenges, for all cars and trucks. Certainly not impossible to drive in 2wd, but why would you if you had awd? Just for the challenge I guess. I also doubt sports car and luxury sedan makers are going to awd just for snow or heavy rains. Its because having power at all four wheels helps even on dry payment for cornering, acceleration, and handling; and even more on wet, loose, or muddy pavement. It is a personal choice in our trucks, so each to their own. I paid for it, and its under warranty, so I am going to use it...all the time...even summer. 4th GM truck and I have never had an issue with the drive train.

aseibel · December 3, 2018

On 12/1/2018 at 7:58 PM, ftwhite said:

You must have sticky-er rain in Green Bay, or better roads. Here in the northwest, we have crumbling roads, and even light rain brings out the oils on the roads and creates traction challenges, for all cars and trucks. Certainly not impossible to drive in 2wd, but why would you if you had awd? Just for the challenge I guess. I also doubt sports car and luxury sedan makers are going to awd just for snow or heavy rains. Its because having power at all four wheels helps even on dry payment for cornering, acceleration, and handling; and even more on wet, loose, or muddy pavement. It is a personal choice in our trucks, so each to their own. I paid for it, and its under warranty, so I am going to use it...all the time...even summer. 4th GM truck and I have never had an issue with the drive train.

maybe up north where we get frequent precipitation, the oil does not build up as much as down south or other places. Maybe all the people who can't drive in 2hi when its raining aren't as crazy as i thought. For me, I can spin my tires if i want to in the rain, but it takes something like 75% throttle to do it. It's not hard to drive around without reaching 75% throttle. If there are road conditions out there where people are spinning the rear wheels with less than 50% throttle, i guess i would use 4 auto in that situation. It was my assumption that 4 auto is for people who need to floor it to pull out into traffic in a gap that was too small to make otherwise. I feel no need to be that aggressive when road conditions are compromised by weather. What if the person you are flooring it to pull in front of isn't paying attention and fails to hit their bakes early enough on the wet pavement so they rear end you? Having the ability to drive all 4 wheels in low traction conditions doesn't mean you need to drive that aggressive in traffic. Now if I want to have fun when no other vehicles are around, that is another story.

4weight · December 3, 2018

On 11/27/2018 at 10:04 PM, Lino said:

Thanks bro... And yes did notice the gas loss.

Just got a 2017 1500 All Terrain and had the same question. Hit the manual and basically on auto the front axle is engaged but is not in 4W high. It clearly says in there your best gas mileage will be in 2W high.

When I picked my truck up it was in Auto and only got 17 per gallon although I was into a headwind most of the trip. Learned my lesson too in the manual.

Edited December 3, 2018 by 4weight