Snow driving - which 4WD mode?

[etoften]

Question. My zr2 has auto 4wd for driving in "mixed conditions". This is the setting for when the highway is dry in sections and ice in others. What do we do in the jeep? Just got 12" of snow. Roads are drying fast. But the wet sections will freeze again tonight. What do we do on a 40 mile curvy commute that's going to be 70% dry and 30% ice / slush?

Sponsored

 

[Heimkehr]

Driving in part-time 4HI on dry surfaces won't damage the axle as some might suggest, provided you're not recurringly making turns sharp enough to cause axle hop (wheel tire scrub.)

In mixed road conditions and sans having Auto 4WD in my JLU, I'll shift into 4HI and drive carefully as conditions compel. No harm to the Jeep, 5+ years on.

 

[etoften]

Driving in part-time 4HI won't damage the axle as some might suggest, provided you're not recurringly making turns sharp enough to cause axle hop (wheel scrub.)

"Part time" 4 hi? Is this a thing? Only have 4 hi and 4 lo.

 

[jadmt]

2wd and slip it into 4 h when the roads are slick

 

[Heimkehr]

"Part time" 4 hi? Is this a thing? Only have 4 hi and 4 lo.

Yes. If your Jeep doesn't have Auto 4WD, as your ZR2 does, then 4HI in the former is part-time. Its use case is described on pp. 154-5 of the 2021 Owner's Manual that you should be reading. Four-position vs. five-position transfer case.

 

[Pape]

Use your jugement, as pointed out 4 hi on dry pavement is not that of issue, the issue start when you do sharp turn and introduce drive line binding.
Happened to me in the past i hit a spot of black ice in 2hi the back end started to slide and the traction control put it back to it place. Just saying 4wd is nice but traction control is the bulk of what keep you in the proper direction except if you are rally driving this is a other story.

 

[Kracka]

Love our Auto4H transfer case!

 

[etoften]

Thanks for all the feedback. Great forum

 

[James Westfall]

70% dry sounds like 2hi conditions to me. It's not like the Wrangler can't move on snow/ice unless it's in 4wd.

I don't understand why the auto-4wd option wasn't more utilized, and then also discontinued, on the Wrangler, however, i've never been held back by not having it.

 

[jeepoch]

@etoften

Eric, it sounds like you don't have the part-time 4wd transfer case. Don't fret, while cool it just means you have to make all the 2wd to 4wd decisions yourself. Not that challenging when you better understand what the Transfer Case (TC) does.

With the standard Command-Trac (manual) TC, moving in to and out of 4wd is straightforward and usually pretty easy to do. Since 2Hi and 4Hi use the exact same high gearing, all you're doing is either engaging or disengaging the drive shaft to the front axle. Nothing more. This is why you can shift the TC lever at higher speeds without needing to slow down.

The typical rule of thumb is to select 4Hi in wet or slippery conditions where more tractive effort is warranted. Selecting from 2Hi to 4Hi or vice versa can be done literally as often as you deem appropriate. Typically reduce throttle, shift the transmission into Neutral or depress the clutch (in order to minimize input shaft torque), push or pull the TC lever to the desired 2 or 4 Hi setting, then reengage the transmission. Easy-peasy, lemon squeezy.

Noting here that all ABS torque control remains enabled and active in Hi gear.

So, with practice it should become second nature to drop in and out of 4wd (high gear) whenever necessary.

The part-time 4wd available on the Select-Trac Transfer Case is specifically designed to do this automatically without any driver intervention. Regardless, both provide the same outcome.

Just keep in mind that you always want to be in 2wd when on dry pavement, in order to reduce binding stresses on both the front and rear differentials, especially while cornering.

Hope this helps.

Safe travels,
Jay

 

[virkdoc]

So what exactly does 4 Auto do? And in Ice do we drive on 4H or 4L? Still a newbie trying to understand this. My jeep does show 4Auto

 

[Ed Pursell]

Selec Trac had the 4 Auto mode along with 4 h and 4 l part time… Command is the part time 4 h and 4 l…


Normal” wrangler transfer cases have three modes: 2H, 4H, 4L. See below from another post… I have a 2021 Willys and I ordered it with the Selec Trac transfer case. It was like a $700.00 option to get the 5 speed transfer.. 2 h, 4a, 4h part time, neutral, and 4l part time.

“Selec trac (as well as the optional version of the Rock trac on the new rubicons) adds a fourth mode: 4A
What you heard is true in regards to 4H & 4L, they should only be used on loose surfaces. (I.e. off road, thick snow, solid ice, etc….). Meaning do not use them on the road.

the 4A option can be used any time, as it defaults to rear wheel drive, and only sends power to the front wheels when needed.

i had selec trac on my 2019 JL, and have the new Rock trac with the 4A on my new Rubicon.”

 

[Fatbob Frank]

I never cared for the 4 Auto ( in my 1500 Ram)
It only really helped taking off from a stop sign.
At highway speeds if your rear end breaks traction it may be too little too late when the front end kicks in.
It's a non-issue in my Powerwagon now or my wife's Willys...Strictly 4Hi or 2Hi the way it should be...
My general rule of thumb is -if you think you may need 4WD just use the 4WD...

 

[etoften]

@etoften

Eric, it sounds like you don't have the part-time 4wd transfer case. Don't fret, while cool it just means you have to make all the 2wd to 4wd decisions yourself. Not that challenging when you better understand what the Transfer Case (TC) does.

With the standard Select-Trac (manual) TC, moving in to and out of 4wd is straightforward and usually pretty easy to do. Since 2Hi and 4Hi use the exact same high gearing, all you're doing is either engaging or disengaging the drive shaft to the front axle. Nothing more. This is why you can shift the TC lever at higher speeds without needing to slow down.

The typical rule of thumb is to select 4Hi in wet or slippery conditions where more tractive effort is warranted. Selecting from 2Hi to 4Hi or vice versa can be done literally as often as you deem appropriate. Typically reduce throttle, shift the transmission into Neutral or depress the clutch (in order to minimize input shaft torque), push or pull the TC lever to the desired 2 or 4 Hi setting, then reengage the transmission. Easy-peasy, lemon squeezy.

Noting here that all ABS torque control remains enabled and active in Hi gear.

So, with practice it should become second nature to drop in and out of 4wd (high gear) whenever necessary.

The part-time 4wd available on the command-Trac Transfer Case is specifically designed to do this automatically without any driver intervention. Regardless, both provide the same outcome.

Just keep in mind that you always want to be in 2wd when on dry pavement, in order to reduce binding stresses on both the front and rear differentials, especially while cornering.

Hope this helps.

Safe travels,
Jay

Thanks for the detail. We bought the jeep as a third vehicle just to drive around on nice days with the top down and back up our aging daily drivers. The ZR2 gets the bulk of the milage.

The Auto 4wd is turn knob and forget. We got a near record 11" of snow here. We aren't equipped to clear that. Going to let my drive the ZR2 for her commute since she won't have to worry about changing anything. I will drive the wrangler. First time and probably last for another 10 years in snow.

 

[jadmt]

I never cared for the 4 Auto ( in my 1500 Ram)
It only really helped taking off from a stop sign.
At highway speeds if your rear end breaks traction it may be too little too late when the front end kicks in.
It's a non-issue in my Powerwagon now or my wife's Willys...Strictly 4Hi or 2Hi the way it should be...
My general rule of thumb is -if you think you may need 4WD just use the 4WD...

ditto...one thing I really like about the power wagon is being able to lock the rear axle in 2hi...pulling onto a busy street that is dry from a side street that is slick makes a big difference. I used that feature a lot. wish my jlur could do similar or better yet wish there was a 2lo wishes and fishes....

Sponsored