4wd modes when to use full time

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

This might sound funny but I’ve never owned a 5 position T case before this Jeep and I’m sort of wondering why anyone would ever use the full time 4x mode? The only thing I can think of is high speed ice driving? But even then, I would probably just use 4wd hi. What’s it for?

WWDiesel · **Posted:** Sat Sep 19, 2020 12:15 pm

From the owner's manual:
Explanans it pretty good.
My understanding is the "Full time" is used for driving on pavement in snowy and icy road conditions.

Jeep Owner's Manual wrote:

The Selec-Trac® transfer case provides 5 mode positions –
1. normal 2-wheel drive mode
2. part-time 4-wheel drive high range
3. full-time 4-wheel drive high range
4. neutral
5. 4-wheel drive low range.

This transfer case is equipped with an inter-axle differential which allows driving the vehicle in the 4 FULL TIME position at all times on any given road surface including dry hard surfaced roads. The 4 FULL TIME mode allows the front and rear wheels to rotate at different speeds which eliminates driveline binding and component wear that is normally associated with driving the vehicle in the 4 PART TIME position on dry hard surfaced roads. This feature provides the safety, security, and convenience of operating in 4–wheel drive at all times regardless of road conditions.

When additional traction is required the 4 PART TIME and 4LO positions can be used to lock the front and rear driveshafts together through the transfer case inter-axle differential and force the front and rear driveshafts to rotate at the same speed. This is accomplished by simply moving the shift lever to these positions.
The 4 PART TIME and 4LO positions are intended for loose, slippery road surfaces only. Driving in the 4 PART TIME and 4LO positions on dry hard surfaced roads may cause increased tire wear and damage to driveline components.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

So it’s for dry hard pavement? I think I’ll keep using 2wd for that lol. As I thought, it’s a useless mode.
I have the same T case in my hmmwv, except they omit the 2wd position. So for that vehicle it is for dry pavement, only because they don’t provide 2wd.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Jett wrote:

So it’s for dry hard pavement? I think I’ll keep using 2wd for that lol. As I thought, it’s a useless mode.

It's not useless. The main advantage of 4FT is that you're not going to risk steering bind while turning because the centre differential allows the front and rear axles to turn at different speeds when unlocked. Effectively, it's an AWD setting.

Advantages: being able to maintain a reasonable speed on hard surfaces in adverse weather conditions with significantly better control of the vehicle; making sharp turns (or turning around) on trails where 4WD is needed.

Quote:

I have the same T case in my hmmwv, except they omit the 2wd position. So for that vehicle it is for dry pavement, only because they don’t provide 2wd.

That's the 242AMG, which also gains a extra chain and external oil cooler over the 242J in the KJ / XJ / ZJ / WJ and a couple of others I'm forgetting. If memory serves, it is possible to engage 2WD with the Hummer case, but shifter linkage (and possibly other) modifications are needed to allow access to it. 2WD isn't 'removed' as such; it's just not accessible in stock form.

Also IIRC (and it's been over a decade since I was last in an HMMWV), that transfer case should have a shift pattern that goes HL-H-N-L. HL is equivalent to 4PT, H is equivalent to 4FT (and is the range that should be used on hard surfaces, including roads), N is also neutral, and L is the same as 4LO. It has the same centre differential as the 242J does, so capabilities are the same.

flash7210 · **Posted:** Sat Sep 19, 2020 2:42 pm

Think of full-time 4wd like all-wheel-drive.
You know, like a Subaru :wink:

I use it during heavy rain.
Great traction and handling on wet and flooded roads.

Mountainman · **Posted:** Sat Sep 19, 2020 3:23 pm

And to add to the above, if you're on icy roads going at a relatively high speed, part time will make you break loose, where as full time will be less likely to do so. Now, if you're going really slow on those same conditions, or roads so slick that you're limited to a max of 25mph or so, then part time is more helpful. But, dont use it if you're going to hit bare pavement or full traction.
I rarely have a road so slick that I use part time on the pavement, only solid ice going very slow...

Offroad, I use part time primarily if I need more traction. Then the lockers when it gets serious.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

casm wrote:

Jett wrote:

So it’s for dry hard pavement? I think I’ll keep using 2wd for that lol. As I thought, it’s a useless mode.

It's not useless. The main advantage of 4FT is that you're not going to risk steering bind while turning because the centre differential allows the front and rear axles to turn at different speeds when unlocked. Effectively, it's an AWD setting.

Advantages: being able to maintain a reasonable speed on hard surfaces in adverse weather conditions with significantly better control of the vehicle; making sharp turns (or turning around) on trails where 4WD is needed.

Quote:

I have the same T case in my hmmwv, except they omit the 2wd position. So for that vehicle it is for dry pavement, only because they don’t provide 2wd.

That's the 242AMG, which also gains a extra chain and external oil cooler over the 242J in the KJ / XJ / ZJ / WJ and a couple of others I'm forgetting. If memory serves, it is possible to engage 2WD with the Hummer case, but shifter linkage (and possibly other) modifications are needed to allow access to it. 2WD isn't 'removed' as such; it's just not accessible in stock form.

Also IIRC (and it's been over a decade since I was last in an HMMWV), that transfer case should have a shift pattern that goes HL-H-N-L. HL is equivalent to 4PT, H is equivalent to 4FT (and is the range that should be used on hard surfaces, including roads), N is also neutral, and L is the same as 4LO. It has the same centre differential as the 242J does, so capabilities are the same.

you are correct, there are some slight differences but very minor and yes I could get a 2wd mode if I really wanted to but I don’t becaue ive swapped a Cummins into my hmmwv and I’m afraid it would doo doo metal if I tried to use 2wd lol.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

flash7210 wrote:

Think of full-time 4wd like all-wheel-drive.
You know, like a Subaru :wink:

I use it during heavy rain.
Great traction and handling on wet and flooded roads.

So it’s for when it rains at the mall. Got it.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

Mountainman wrote:

And to add to the above, if you're on icy roads going at a relatively high speed, part time will make you break loose, where as full time will be less likely to do so. Now, if you're going really slow on those same conditions, or roads so slick that you're limited to a max of 25mph or so, then part time is more helpful. But, dont use it if you're going to hit bare pavement or full traction.
I rarely have a road so slick that I use part time on the pavement, only solid ice going very slow...

Offroad, I use part time primarily if I need more traction. Then the lockers when it gets serious.

I think I agree with your assessment. It’s for warp speed on ice. Even tho I don’t mind warp speed on ice in any of my true 4wd rigs, because the edict about “dry pavement winding up your driveline” is really only applicable to sharp turns at slow speed. So, it’s a fairly use,ess mode but I’ll try to find use for it someday.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

Ooh I just thought of the perfect use! It’s for trailer pulling/maneuvering on uneven ground that might also be dry.

geordi · **Posted:** Sat Sep 19, 2020 5:29 pm

4WD does not increase your traction. It MIGHT increase the torque applied to the road, but if you are towing that heavy that 2WD isn't sufficient... You are likely WAY over what the engine should be pulling.

PZKW108 · **Joined:** Sun Apr 06, 2014 5:23 pm **Posts:** 461

geordi wrote:

4WD does not increase your traction. It MIGHT increase the torque applied to the road, but if you are towing that heavy that 2WD isn't sufficient... You are likely WAY over what the engine should be pulling.

Traction is the friction between tires and the ground that allows a vehicle to move forward. It is the resistance to spinning when a torque is applied to axle the wheel. When a surface is wet, a layer of water can act as a lubricant, greatly reducing the traction and stability of the vehicle.

You don't need to reinvent the wheel geordi :dizzy:

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

geordi wrote:

4WD does not increase your traction. It MIGHT increase the torque applied to the road, but if you are towing that heavy that 2WD isn't sufficient... You are likely WAY over what the engine should be pulling.

Is this some sort of engineering humor or just nonsense? Lol. 4wd does increase traction, that’s literally the entire point of it. And when I say use it for towing I mean like parking a trailer, on gravel on a hill, where you are maybe steering lock to lock in reverse....
oh never mind it’s a useless mode that literally nobody uses probably.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Jett wrote:

geordi wrote:

oh never mind it’s a useless mode that literally nobody uses probably.

Having had multiple Jeeps with both the NP231 and NP242 transfer cases, I'll take an NP242 over an NP231 any day. 4FT is a large part of the reason for this - when it's needed, it's invaluable. It may not be obvious what the value is, but I can say from experience owning a variety of 4WD and AWD vehicles, it's made me a fan of lockable centre diffs.

PZKW108 · **Joined:** Sun Apr 06, 2014 5:23 pm **Posts:** 461

casm wrote:

Jett wrote:

geordi wrote:

oh never mind it’s a useless mode that literally nobody uses probably.

Having had multiple Jeeps with both the NP231 and NP242 transfer cases, I'll take an NP242 over an NP231 any day. 4FT is a large part of the reason for this - when it's needed, it's invaluable. It may not be obvious what the value is, but I can say from experience owning a variety of 4WD and AWD vehicles, it's made me a fan of lockable centre diffs.

Same here !

I do a lot of fast pace winding gravel roads and 4FT is the ticket ! For any season.

WWDiesel · **Posted:** Sat Sep 19, 2020 9:39 pm

geordi wrote:

4WD does not increase your traction. It MIGHT increase the torque applied to the road, but if you are towing that heavy that 2WD isn't sufficient... You are likely WAY over what the engine should be pulling.

4WD does increase applying motivational power to the ground with all four tires provided the tires can get traction on something.
Having been in some very serious situations where gooey slippery Georgia swamp mud was involved, I can fully attest to the benefits of having 4WD.

4WD is just like a Winch, neither one is worth a darn until you need either one or both of them; then there is absolutely nothing else like them.
Speaking from experience; been there done that. :wink:

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

PZKW108 wrote:

casm wrote:

I do a lot of fast pace winding gravel roads and 4FT is the ticket ! For any season.

Agreed - been there, done that, repeated the experience :mrgreen:

As another example: we get severe weather in this neck of the woods. Tornadoes aren't uncommon, but neither are strong (50mph+) winds or heavy rain (2 inches or more in an hour). Sometimes, this sort of weather is unavoidable. Being able to get as much power to the ground at speed while you GTFO as far as possible from the problem is the difference between going home or injury and/or death. I'm not overstating the issue; our weather kills people on a fairly regular basis.

Even when I lived in the Southern California monoseason, having 4FT was hugely preferable to not. The roads there (except at high altitude) were not surfaced for weather, and a quarter-inch of rain would turn them into hydroplane nightmares. And on the trails in that part of the world, 4FT (where usable) gave much better turning capability on switchbacks as well as other tight-turn situations - not to mention that at speed over sand or other loose surfaces, control was much improved.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

PZKW108 wrote:

I do a lot of fast pace winding gravel roads and 4FT is the ticket ! For any season.

Okay I can see that being a good use. Basically the same as ice driving.

layback40 · **Posted:** Sun Sep 20, 2020 2:54 am

It shows those who have owned a 4wd without the FT function. FT is like a car with AWD.
I find that when there is rain after a long dry spell & smooth bitumen in town becomes a bit greasy, FT stops the jeep from fish tailing when turning in a hurry & you hit the slippery white line. In FT the drive is distributed to both front & back so there is less torque being applied to the rear wheels as some is going to the front.
If you think its just a gimmick thats fine, you dont have to use it!

krb · **Posted:** Sun Sep 20, 2020 6:22 am

4FT saved my butt several years ago and made be a believer.

We had a snow & ice storm and my daughter was 4.5 hours away at college in a toxic situation with a roommate that went dangerous. So ol' dad set out in the new to me KJ with an extra 5 gallons of diesel, blankets, food & water, S&W.38+P, plus shovel, chain etc. around 3 a.m.

Anyway, most of the driving was on the parkway with semis and all the SUV drivers that have no clue how to drive (or stop) in snow. I soon learned that the road would change from clear pavement to snow covered to one lane open to black ice at the blink of an eye - mainly at interchanges where the plow truck would switch directions...

If I drove at a safe comfortable speed I'd be overrun by semis or the crazy SUV drivers which was ok when we had two lanes open but scary with only one or none. Worst thing was going around a bend to find a lane blocked by a stuck semi and everyone panic funneling into the "open" lane. 4FT was wonderful!

Once I got to my destination, their 6" of snow was topped by freezing rain so it was solid corn ice. I drove around like it was a normal summer day dodging all the manhole cover craters where it all had melted. 4FT was wonderful.

I'm used to that mode though, my 1977 M880 (W200) has a permanent version. I drove home from work one day in it during another ice storm. On hills I'd have to put one set of tires on the shoulder or ditch for traction.

I don't need it often but when I do it's invaluable to me. :pepper:

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4wd modes when to use full time

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