Auto vs 2H Settings...

[Andy Seibel]

once last winter i had it in 4wd when i left home on icy roads. (I had recently finished plowing and just parked it in 4wd because i did not know about the recall yet) I then drove through town (snowy roads) and forgot about it, and got on the freeway which was clear and dry. I drove over 100 miles in 4wd with no issues. But as soon as i exited and made a turn, i sure knew the 4wd was on, so i immediately put it back in 2wd.

 

As long as all 4 wheels are turning the same speed you are not putting any stress on the system, so you can drive a million miles in a straight line in 4wd. But once you turn a corner on dry pavement you are stressing the 4wd system and wearing rubber off you tires like an eraser on paper.

[Donstar]

It is fairly recent that 4 wd pickups were so common or mainstream. Where I live, 2 wd 1/2 tons are now as scarce as regular cabs on the dealers' lots! The majority of us don't need 4wd for our everyday driving needs, but it is fun to have for recreational activities or for peace of mind in inclement weather. The one point I like to make whenever this topic comes up is don't use 4 wd to compensate for poor tires. If you are regularly "breaking traction" during normal rain, chances are you're on OEM or minimal quality tires.

[powerhaulic]

It is fairly recent that 4 wd pickups were so common or mainstream. Where I live, 2 wd 1/2 tons are now as scarce as regular cabs on the dealers' lots! The majority of us don't need 4wd for our everyday driving needs, but it is fun to have for recreational activities or for peace of mind in inclement weather. The one point I like to make whenever this topic comes up is don't use 4 wd to compensate for poor tires. If you are regularly "breaking traction" during normal rain, chances are you're on OEM or minimal quality tires.

Very true

Exactly why I traded my tires in within the first week of ownership of new truck. (Michelin Defenders)

 

I live in the Adirondack mts. and have a steep driveway, we typically get over 100" of snow each winter. I remove and replace each year with dedicated snows on another set of wheels too. (Firestone Winterforce)

[Silverado Steve]

Surprisingly, I rarely use my 4wd system, or at least 4HI. If there is any snow accumulation or ice on the ground, I put it in 4Auto, and rarely ever use 4Auto when it's wet outside. I think a lot can be done with a set of good tires and Traction control and careful throttle with a 2WD truck, but I also understand 4wd can help immensely in low traction situations. With that being said, I too would only buy a 4wd truck. I believe better to have and not need, then need and not have. Plus being in the military, you can be stationed in Florida one year and Alaska the next...I know a lot of people who took baths on their Bimmer's, Camaro's, Mustang's...etc moving from Texas to Colorado.

[brians09]

Take this with a grain of salt because this is just hearsay from the dealer.. But last time I went in I asked about leaving it in auto and the tech said don't do it unless you really need the traction. He said he's had to replace a hand full of t-cases in soccer mom Tahoe/suburban at around 80k miles because they leave it in auto on wet and dry surfaces. This is also in California where we have no rain, so who knows..

 

 

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[truckguy82]

umm, I don't think so, Tim.

 

The auto system can't send power to specific wheels. It only senses slipping of the rear and and then engages the front axle so you temporarily have 4wd. It would cause excessive wear on the system and tires to be having it shift in and out of 4wd continuously. That is why an intelligent driver can decide if the conditions require 4wd or 2wd and select the range accordingly. But you do whatever you want with your truck. leave it in auto all the time "because you can".

Ok so there's a front differential and a rear differential, they'll allow different rotation speed the left to right side. The real damage from locked in 4wd happens when you don't have a center differential and the front and rear are turning at different speed (ie a tight turn). But being as the "auto" feature is only activated with slipping of the rear axle, it means there shouldn't be any or very little wear and tear on the transfer case.

 

I mean I'm not sure on the actual difference. But most awd systems are bias to one set of drive wheels and are clutch activated just like 4auto and you obviously cannot turn them off. In my limited understanding of the systems, it seems like there is no difference between the 4auto setting and awd.

 

If anybody knows the difference please chime in

[SouthernSilveradoGuy85]

Ok so there's a front differential and a rear differential, they'll allow different rotation speed the left to right side. The real damage from locked in 4wd happens when you don't have a center differential and the front and rear are turning at different speed (ie a tight turn). But being as the "auto" feature is only activated with slipping of the rear axle, it means there shouldn't be any or very little wear and tear on the transfer case.

 

I mean I'm not sure on the actual difference. But most awd systems are bias to one set of drive wheels and are clutch activated just like 4auto and you obviously cannot turn them off. In my limited understanding of the systems, it seems like there is no difference between the 4auto setting and awd.

 

If anybody knows the difference please chime in

 

 

Wrong. An AWD system has the ability to send a certain amount of power to each wheel individually. With a 4wd system it's just 50/50. What you're talking about is one side has to be able to turn at a different speed when turning. That doesn't mean one wheel has more power than the other.

[sdeeter19555]

Ok so there's a front differential and a rear differential, they'll allow different rotation speed the left to right side. The real damage from locked in 4wd happens when you don't have a center differential and the front and rear are turning at different speed (ie a tight turn). But being as the "auto" feature is only activated with slipping of the rear axle, it means there shouldn't be any or very little wear and tear on the transfer case.

 

I mean I'm not sure on the actual difference. But most awd systems are bias to one set of drive wheels and are clutch activated just like 4auto and you obviously cannot turn them off. In my limited understanding of the systems, it seems like there is no difference between the 4auto setting and awd.

 

If anybody knows the difference please chime in

Keep in mind that I don't know how the transfercase guts operate in one of the auto 4wd trucks (assuming it's an electrically-actuated clutch of some sort).

 

The only added wear I could see in auto 4wd is when the transfercase engages...and whatever mechanism engages it. Otherwise, it would engage momentarily until it senses no speed difference between the front and rear wheels, then disengage like a normal 2wd. I'd be more worried about chain stretch in the transfer case from the potentially frequent and abrupt engagements than wear of any other component. The truck needs to sense slipping between the front and rear wheels, so there is going to be a shock load applied at some point.

 

I see two questions for the auto 4wd trucks...

 

1) do they have a front differential engagement deal like the non-autos? In other words, would the front differential be spinning all the time anyway or does it also disengage when not in auto 4wd? I can't see how it could have the front differential engage/disengage everytime 4wd was demanded (too slow for that, at least mine is). If they don't have engagement at the front differential, then those components spin all the time anyway.

 

2) what is the life expectancy of the transfer case and its actuator?

 

 

 

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[truckguy82]

 

 

Wrong. An AWD system has the ability to send a certain amount of power to each wheel individually. With a 4wd system it's just 50/50. What you're talking about is one side has to be able to turn at a different speed when turning. That doesn't mean one wheel has more power than the other.

I'm pretty sure that's not true at all in regards to awd systems sending power to individual wheels.

 

Maybe advanced systems like acura sh-awd and the focus RS. Even then, there's only so much you can do to convert the power of one engine and one transmission into powering 4 tires seperately.

 

If that were the case awd would dominate off road, and they don't.

[Knotsure]

My 2006 GMC Sierra 4wd with auto4 had 187000+ miles in it. I changed the little donut sensor in the transfer case actuator (I don't remember the exact part) at around the 140000. If my 14 is anywhere near that I will be happy.

 

 

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[SouthernSilveradoGuy85]

I'm pretty sure that's not true at all in regards to awd systems sending power to individual wheels.

 

Maybe advanced systems like acura sh-awd and the focus RS. Even then, there's only so much you can do to convert the power of one engine and one transmission into powering 4 tires seperately.

 

If that were the case awd would dominate off road, and they don't.

 

 

I woudln't say that AWD would dominate off-road since AWD is essentially 4hi all the time. In the more extreme types of off-roading you'll need 4lo. Also the front axle, unless it has some type of locker, only power 1 wheel like an open diff. There's really no reason to even compare AWD and 4x4 (even auto 4) since the systems are different and made for different things.

[truckguy82]

Keep in mind that I don't know how the transfercase guts operate in one of the auto 4wd trucks (assuming it's an electrically-actuated clutch of some sort).

 

The only added wear I could see in auto 4wd is when the transfercase engages...and whatever mechanism engages it. Otherwise, it would engage momentarily until it senses no speed difference between the front and rear wheels, then disengage like a normal 2wd. I'd be more worried about chain stretch in the transfer case from the potentially frequent and abrupt engagements than wear of any other component. The truck needs to sense slipping between the front and rear wheels, so there is going to be a shock load applied at some point.

 

I see two questions for the auto 4wd trucks...

 

1) do they have a front differential engagement deal like the non-autos? In other words, would the front differential be spinning all the time anyway or does it also disengage when not in auto 4wd? I can't see how it could have the front differential engage/disengage everytime 4wd was demanded (too slow for that, at least mine is). If they don't have engagement at the front differential, then those components spin all the time anyway.

 

2) what is the life expectancy of the transfer case and its actuator?

 

 

 

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What I think happens when you flip it to auto.... you engage the transfer case actuator into 4wd as every other truck has done for the last 20 years, but there is a clutch somewhere in between the front differential and the transfer case. Normally the clutch is disengaged, and when you lose traction the clutch engages. I'm pretty sure that's out most clutch type limited slip differentials operate.

 

I mean my wife's acura rdx, i know when i was hooliganing in the snow it gave me a service message that the awd clutch fluid was too hot.

 

Subaru's, i know you can pull a fuse to disengage the awd clutch that sends power to the rear tires.

 

Both these "awd" vehicles are front biased systems have a clutch that transmits power to the rear.

 

How that's different from our trucks I can't figure out.

[truckguy82]

 

 

I woudln't say that AWD would dominate off-road since AWD is essentially 4hi all the time. In the more extreme types of off-roading you'll need 4lo. Also the front axle, unless it has some type of locker, only power 1 wheel like an open diff. There's really no reason to even compare AWD and 4x4 (even auto 4) since the systems are different and made for different things.

Yeah but what mechanical components precisely makes awd different from auto4.

 

Both have differentials front and rear and both transmit power front and rear via clutch.

 

I seriously am trying to figure this out, I'm not concluding they are the same thing.

[SouthernSilveradoGuy85]

Yeah but what mechanical components precisely makes awd different from auto4.

 

Both have differentials front and rear and both transmit power front and rear via clutch.

 

I seriously am trying to figure this out, I'm not concluding they are the same thing.

 

I guess this is a situation where Youtube is your friend. Think about it though. If they were the same then it would be safe to drive in 4hi all the time and it certainly isn't. I personally, like I've stated, don't agree with putting it in 4auto even in the rain. Too me just a wet road still has more grip than you think and has more grip than snow or ice which is what 4 auto is for. It's for inconsistent road conditions. It says that in the manual. Which is if it switches between snow/ice/slush and asphalt that's just dry or wet from when snow and ice melts.

[sdeeter19555]

In reality, AWD only means that any ONE of the four tires will be driven at any one time, not that all four will necessarily be driven at any one time. The advent of electronically-controlled clutches and speed sensors that clamp individual calipers on spinning wheels is what makes the modern AWD systems superior on slippery surfaces (read: surfaces, not buried up to the body in mud).

 

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