When to NOT use 4WD AUTO ?

[NorskieRider]

When shouldn't I use 4WD AUTO ? (2026 w/5-position selector, not RHO)

I ask because my neighborhood is often ice and snow and I need 4WD to get up my driveway and in/out of the neighborhood, but I can get around town in 2WD.
When I get out on the highway I'll usually switch to 2WD, except in blizzard conditions last night and 'highway speeds' was < 45 mph.

Part of my question arises from the ignorance of the mechanicals in this driveline.

The manual states this, suggests it won't hurt anything:

Four-Wheel Drive Automatic High Range (4WD AUTO)
— This range sends power to the front wheels
automatically when the vehicle senses a loss of
traction. This range may be used during varying road
conditions.

That suggests it's basically 4X4 when it needs to be, and more it senses a loss in traction is switches as needed, which seems to imply a lot of work on part of the transfer case shifting in and out of 4WD AUTO.

Interestingly, the RHO section describes 4WD AUTO differently:

Four-Wheel Drive Auto High Range — This range always
sends power to the front wheels and automatically
adjusts the front and rear torque split to optimize
performance for the operating conditions. For example,
when the vehicle senses a loss of traction. This range
may be used during varying road conditions.

That sound more like a standard FWD-biased AWD system.

So ... smarties .... my questions:

1. Is frequent (2+ times per trip) shifting between 2WD and 4WD AUTO detrimental to the transfer case?
2. Is driving in 4WD AUTO at highway speeds detrimental?
3. Is driving around all day at city speeds in 4WD AUTO detrimental to the transfer case? (I know 4WD HIGH or LOW is). I'm guessing is a lot of "shift on the fly".
4. Does the RHO have a different 4WD AUTO system or is the user's guide wrong?

 

[vincentw56]

When shouldn't I use 4WD AUTO ? (2026 w/5-position selector, not RHO)

I ask because my neighborhood is often ice and snow and I need 4WD to get up my driveway and in/out of the neighborhood, but I can get around town in 2WD.
When I get out on the highway I'll usually switch to 2WD, except in blizzard conditions last night and 'highway speeds' was &lt; 45 mph.

Part of my question arises from the ignorance of the mechanicals in this driveline.

The manual states this, suggests it won't hurt anything:

That suggests it's basically 4X4 when it needs to be, and more it senses a loss in traction is switches as needed, which seems to imply a lot of work on part of the transfer case shifting in and out of 4WD AUTO.

Interestingly, the RHO section describes 4WD AUTO differently:



That sound more like a standard FWD-biased AWD system.

So ... smarties .... my questions:

1. Is frequent (2+ times per trip) shifting between 2WD and 4WD AUTO detrimental to the transfer case?
2. Is driving in 4WD AUTO at highway speeds detrimental?
3. Is driving around all day at city speeds in 4WD AUTO detrimental to the transfer case? (I know 4WD HIGH or LOW is). I'm guessing is a lot of "shift on the fly".
4. Does the RHO have a different 4WD AUTO system or is the user's guide wrong?

The only answer is when you want to save on gas. That's the answer from Ram. I watched a video on it with one of the Ram employees (engineer maybe?).

And yes, the RHO and TRX both use 4WD Auto differently than the regular 1500s.

 

[CHeYeNNe71]

 

[vincentw56]

Yes, that's the video I watched. It was mentioned that fuel economy is the only true benefit from not using it all the time.

 

[skny]

My understanding is when 4Auto - the front wheels are semi engaged all the time using a clutch to increase or decrease the engagement according to sensed slip (I probably didn’t explain it super accurately but thinks it’s close enough). When it’s on, you can feel it when slowing down on normal dry pavement - at least I and many others can. It’s a slight shudder / friction type feel. I leave it off - unless I know I’m going to be in potentially slick conditions & don’t want to put it into 4 Hi or 4 Low explicitly.
I prefer the way the truck rides & feels in 2WD during normal paved road driving. With that said - I believe I read that failure to use it periodically could cause it to fail sooner - the belief similar to not using a parking brake for a long time - then trying to use it and it breaks. Same goes with switching to 4HI / 4Low. Good idea to at least periodically enable these - properly of course (dirt, snow etc & not dry pavement while turning).
Again - I may not have explained properly - but 4WD Auto has been discussed in great detail in different groups / forums with people way smarter then me explaining the technicals behind it - and what I provided is what I feel is the gist of things.

 

[Grimlakin]

The 4wd system in non RHO's and probably in full RHO's is a clutch plate. Depending on needs as slip is detected the system will allocate power to the front tires as needed. In the RHO there is always some power distributrion because the intended use case is different than someone who might pop into 4wA for towing or weather.

Personally I use 4wA if it's even misty outside... with the crazy torque and power these trucks can put down and the lighter rear end... it just feels like it makes sense. Heck even on a perfect day pulling out of the carwash onto the road I can spin the back tires not even aggressively accelerating in 2wD mode. And I have the standard output Hurricane.

 

[Granite Goat]

I use 2wd most of the time. If nothing else, it forces me to at least try to drive gently as to not spin the tires. But if it is remotely slippery, I've been using 4WD Auto. I do not think that leaving it in 4WD Auto most of the time does any harm as long as you cycle through the modes once in a while.

 

[John Kloehr]

Did not know there were two systems, makes me wonder which my '22 Rebel has. Anyway, I use it in the rain or snow. It costs about a mile per gallon when engaged. I therefore suspect the front diff and maybe CVs are engaged just waiting for the hubs to get a lock command on slippage. This is also in line with auto-4wd on a '00 2500 Suburban I used to have.

I have not noticed anything different in the way the truck drives in auto-4wd as long as it does not engage, except maybe some hint of additional driveline noise.

Engagement on slip is very controlled and helpful. This might be due to snow or ice, mainly use it for a certain intersection where I am at a stop facing uphill in the rain. The rear will spin without it, and just drive nice when engaged. There is another spot with gravel from road repair on a right corner (again, at a stop sign). Nice to just drive around it with auto-4wd rather than carefully feathering the gas.

When not to use it? A dry clear highway or otherwise good clean roads. And being aware of the cost to fuel economy. I found nothing in the owners manual saying not to use the automatic feature.

 

[vincentw56]

Did not know there were two systems, makes me wonder which my '22 Rebel has. Anyway, I use it in the rain or snow. It costs about a mile per gallon when engaged. I therefore suspect the front diff and maybe CVs are engaged just waiting for the hubs to get a lock command on slippage. This is also in line with auto-4wd on a '00 2500 Suburban I used to have.

I have not noticed anything different in the way the truck drives in auto-4wd as long as it does not engage, except maybe some hint of additional driveline noise.

Engagement on slip is very controlled and helpful. This might be due to snow or ice, mainly use it for a certain intersection where I am at a stop facing uphill in the rain. The rear will spin without it, and just drive nice when engaged. There is another spot with gravel from road repair on a right corner (again, at a stop sign). Nice to just drive around it with auto-4wd rather than carefully feathering the gas.

When not to use it? A dry clear highway or otherwise good clean roads. And being aware of the cost to fuel economy. I found nothing in the owners manual saying not to use the automatic feature.

There are 2 systems, yes. But there is one that is selectable and one that is not. The one on the RHO and TRX are in 4WD Auto by default. They do not have a 2WD option. There's no guessing which one your Rebel has.

 

[NorskieRider]

Thanks - that's the kind of information I'm looking for! Also found this:

which was helpful in having diagrams etc.

So the 5th gen uses wet clutches - much like most motorcycles - to send torque to the front axle. It's not like a traditional transfer case with forks etc. engaging sprockets. In 2WD the clutches don't send any power to the front, in 4WD HI or LO it they are fully engaged and have no slippage (wear) and in 4WD AUTO they slip to some degree. Being wet clutches, assuming they're not abused, they should last long past the time the body succumbs to a pile of rust.

So the answer to my questions: Just leave it in 4WD until I get on the highway and it's safe to get another MPG or so.

 

[vincentw56]

Thanks - that's the kind of information I'm looking for! Also found this:

which was helpful in having diagrams etc.

So the 5th gen uses wet clutches - much like most motorcycles - to send torque to the front axle. It's not like a traditional transfer case with forks etc. engaging sprockets. In 2WD the clutches don't send any power to the front, in 4WD HI or LO it they are fully engaged and have no slippage (wear) and in 4WD AUTO they slip to some degree. Being wet clutches, assuming they're not abused, they should last long past the time the body succumbs to a pile of rust.

So the answer to my questions: Just leave it in 4WD until I get on the highway and it's safe to get another MPG or so.

Pretty good video, but it must get really tiring flailing your arms around while you talk all the time.

 

[OlegShv]

I am in Alaska. I use 4Auto pretty much all winter long and on wet pavement during summer months. If we have dry pavement I use 2WD. I engage 4High when we get significant snowfall (5 inches or more). 4High works fine as long as the road surface is very slippery, I.e. compacted snow with ice. If it snows less than 3 inches they won’t even plow the roads here.

In 4Auto it engages the front axle but only sends about 5-10% of torque there. If it senses slippage in the rear wheels, it sends more torque to the front. In 4High torque distribution is 50-50% front to rear axles.

Given the wet clutch transfer case design, driving in the city or on the highway in 4A is fine even with dry pavement. Regarding the frequency of shifting - I think it is a good idea to shift the transfer case periodically through all modes, say once a month.