Would you get the the rock-trac t-case for your rubicon if you could do it all over again?

grimmjeeper

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The HMMV also used a 242AMG, but it was built differently and MUCH stronger than the XJ 242. My guess is the new full-time system is not built as was the old XJ 242, but something stronger. My comments were really about the utility of the full-time setting, which I used regularly in my XJ.
Yeah, there are several different grades of NP242 transfer cases.

And I guarantee that the current "auto 4WD" case that comes in the JL is entirely different. The 242 had no limited slip or provision for any kind of electronic clutch. It really is an open differential inside the case when you're in full time 4 hi. If you have one tire on wet ice or mud and open differentials in the axles, it's the only tire that will spin when in full time. Though with a TrueTrac front and rear, the full time 4hi mode in the XJ is really great in all weather driving. I recently sold my XJ that was set up like that. Along with good tires, it was just about unstoppable in any snow less than a foot deep.

It will be interesting to see how the JLU does in snow this coming winter. I put the same kind of tires on it but I don't have limited slip or full time 4 hi. I just have the Rubicon lockers and part time 4 hi.

Still, I think I'll manage just fine.
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Reinen

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I am wondering where anybody got the idea that the "full time" transfer case doesn't use a chain drive? There is still a chain that transfers the power to the front driveshaft. The difference is the addition of an electronically controlled clutch pack that engages that chain based on feedback from wheel speed sensors. It is still a fairly standard part time transfer case and most definitely uses a chain.
Then why is the front driveshaft so much wider and the transfer case the same size? Where is that clutch pack exactly? Seems to me like the transfer case is doing its usual 4WD HI thing and the front axle is allowing just enough slip to accommodate different wheel speeds in turns but engages if the slip exceeds that. That's where the automatic engagement kicks in. Wouldn't even need wheel speed sensors for that. In fact, I had a wheel speed sensor go out. Many things stopped working because of that but 4WD Auto wasn't on the list.

BTW, I'm not saying I know. Just that from what I figured out so far, that's what makes the most sense to me.
 

grimmjeeper

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Then why is the front driveshaft so much wider and the transfer case the same size? Where is that clutch pack exactly? Seems to me like the transfer case is doing its usual 4WD HI thing and the front axle is allowing just enough slip to accommodate different wheel speeds in turns but engages if the slip exceeds that. That's where the automatic engagement kicks in. Wouldn't even need wheel speed sensors for that. In fact, I had a wheel speed sensor go out. Many things stopped working because of that but 4WD Auto wasn't on the list.

BTW, I'm not saying I know. Just that from what I figured out so far, that's what makes the most sense to me.
Most of them that I've seen apart have a clutch pack between the main shaft and the gear that drives the chain. So it's buried inside the main part of the case.

I've seen a couple that have the clutch/engagement point on the front output shaft. So the chain ends up spinning all the time and the front output shaft doesn't always spin.

I've never seen any system that uses the driveshaft to do anything but connect the case to the axle. Actuating any kind of engagement in the driveshaft would be way more complicated than it's worth.

A bigger diameter shaft with the same wall thickness is generally stronger. I'm not sure if that's the case with the JL or not.
 

Reinen

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A bigger diameter shaft with the same wall thickness is generally stronger. I'm not sure if that's the case with the JL or not.
On my '21 JL w/ 4WD Auto the front driveshaft is at least twice the diameter of the rear driveshaft. Leads me to believe there is something more than a plain 'ol driveshaft up front.
 

grimmjeeper

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On my '21 JL w/ 4WD Auto the front driveshaft is at least twice the diameter of the rear driveshaft. Leads me to believe there is something more than a plain 'ol driveshaft up front.
Diameter alone doesn't mean anything.

Are there any collars on it with connectors for wires or vacuum lines or anything? If not, how could the shaft know when to "shift" anything?

No. All of the action happens inside the transfer case. The diameter of the shaft has nothing to do with full time/part time workings.
 

Vrrooom

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Blows me away the driving responsibilities people are willing to abdicate to computers... If the road looks slippery, use 4wd. I do not understand relying on the reactionary engagement when your own eyes and butt should be able to discern whether or not you need 4wd.

I think the CV's are fine, that wouldn't worry me. It is just a "luxury option" for the lazy to have auto engagement. I have lived in big snow country all my life. I have had auto engagement systems. I would never purposely order one and pay extra for it myself.
I'm not sure if this is really about abdicating driving responsibilities. If you live in an area that has roads that are plowed, you will be driving between dry and slick pavement. Making turns on these conditions while in 4hi will cause the vehicle to 'push' and sometimes bind if its dry enough. Higher speed stability is also sacrificed in turns during slick conditions (this includes rain, sleet, snow, etc.) In these situations a 4auto setup is actually safer.

You'll see many people post real life experience and examples of how a wrangler is not so good at higher speeds in adverse conditions. The reason is Wranglers usually have either 2hi or 4hi. 4auto helps in this arena and makes the vehicle safer. And when I say higher speed, I don't mean driving excessively fast. 40-50 mph is plenty to start noticing the shortcomings of either 2hi or 4hi on slick roads and turns.

So why not get it if it makes your vehicle safer to you and those around you in your driving conditions? But agreed, it isn't for everyone.
 

Ridgway Jeeper

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Then why is the front driveshaft so much wider and the transfer case the same size? Where is that clutch pack exactly? Seems to me like the transfer case is doing its usual 4WD HI thing and the front axle is allowing just enough slip to accommodate different wheel speeds in turns but engages if the slip exceeds that. That's where the automatic engagement kicks in. Wouldn't even need wheel speed sensors for that. In fact, I had a wheel speed sensor go out. Many things stopped working because of that but 4WD Auto wasn't on the list.

BTW, I'm not saying I know. Just that from what I figured out so far, that's what makes the most sense to me.
It is in the transmission side of the t-case. The engagement is very much the same as a standard t-case with the exception of being electronically variable. So the fork that engages the front drive via the chain is motor controlled, not just on a fork with a lever attached.

Exploded view at http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=25830

It is definitely not in the driveshaft. I have no idea why that would be substantially larger.
 

MrMischief

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If the auto 4 hi was an option when I bought my Jeep I probably would have opted for it. What I often found is I'll be in 4 hi getting in to work but as I turn into the parking garage I'm now on a high traction surface. Not that big of a deal, push it into 2wd as you go into to the turn. Even in snow/ice covered parking lots I'd often go into 2wd just to get that tighter turning circle, 4wd often causes understeer making it more difficult to make tight turns. If I was in a place where someone else was driving my Jeep I'd find it much easier to tell them to just use 4 auto rather than trying to explain the time/place for 2wd in a snow storm.

Also... I'm the guy who goes 85+ in a TJ across Wyoming in winter, pulling it in and out of 4 high depending on road conditions. It's often clear roads except where the snow has been blown across, melts, then refreezes at night. 4 auto would probably make my life easier. And no, slowing down is not an option. As I said, Wyoming.

I don't see a use for 4 auto outside of snow/ice conditions. OP is from PNW, depending on what exactly that means I see it going either way. If you're in MI, 4 auto makes sense. Nevada, probably not so much. Texas? If you're from Texas you need all the help you can get when it comes to driving so just get it.
 

Ridgway Jeeper

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I'm not sure if this is really about abdicating driving responsibilities. If you live in an area that has roads that are plowed, you will be driving between dry and slick pavement. Making turns on these conditions while in 4hi will cause the vehicle to 'push' and sometimes bind if its dry enough. Higher speed stability is also sacrificed in turns during slick conditions (this includes rain, sleet, snow, etc.) In these situations a 4auto setup is actually safer.

You'll see many people post real life experience and examples of how a wrangler is not so good at higher speeds in adverse conditions. The reason is Wranglers usually have either 2hi or 4hi. 4auto helps in this arena and makes the vehicle safer. And when I say higher speed, I don't mean driving excessively fast. 40-50 mph is plenty to start noticing the shortcomings of either 2hi or 4hi on slick roads and turns.

So why not get it if it makes your vehicle safer to you and those around you in your driving conditions? But agreed, it isn't for everyone.
You are kind of counting on the system to be able to "see" the road, which it simply can not do again despite claims that it is somehow proactive.

Having a little push or bind is something that simply comes with part time 4wd, it isn't really that big of a deal if you are used to how it functions.

To me it is a massive leap of faith. I do not want the vehicle making decisions for me, simple as that. Learning to use the tool properly seems much "safer" to me rather than assuming it can see the road as well as you.

I think the feature is offered and obviously there is a demand for "no brainer" systems. I still see it as abdicating your driving responsibilities to a machine with no eyes. That makes me uncomfortable. Clearly it makes others more comfortable.

I think it is a leap to claim it makes your vehicle safer. I feel a good driver is what makes a vehicle safer, not blind automatic reactionary "safety systems".
 

Reinen

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It is in the transmission side of the t-case. The engagement is very much the same as a standard t-case with the exception of being electronically variable. So the fork that engages the front drive via the chain is motor controlled, not just on a fork with a lever attached.

Exploded view at http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=25830

It is definitely not in the driveshaft. I have no idea why that would be substantially larger.
That's exactly what I was unable to find. Thanks for clearing that up!
So now I have no idea why the front driveshaft is substantially larger either. :)
 

GATORB8

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It is in the transmission side of the t-case. The engagement is very much the same as a standard t-case with the exception of being electronically variable. So the fork that engages the front drive via the chain is motor controlled, not just on a fork with a lever attached.

Exploded view at http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=25830

It is definitely not in the driveshaft. I have no idea why that would be substantially larger.
Who'd have thought the answer would have been on a Jeep Liberty forum, haha.

Looking into this has certainly been a lesson in Jeeps 4wd naming scheme.

Both Command Trac and Rock Track PT are the same NV241 with different low range
Both Select Trac and Rock Trac FT are MP3022s with different low range, and the 392 is the same thing with 2wd locked out electronically.
 
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Reinen

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You are kind of counting on the system to be able to "see" the road, which it simply can not do again despite claims that it is somehow proactive.

Having a little push or bind is something that simply comes with part time 4wd, it isn't really that big of a deal if you are used to how it functions.
But it isn't a matter of learning to use the tool properly. It's a matter of knowing there is an inherent flaw in the tool. It is impossible to make a turn in 4WD without a tire breaking traction. On snow & ice, once you break traction it's much more difficult to regain it than on summer surfaces.

The only time 4WD benefits you on snow & ice is when you're trying to accelerate forward. It turns it's detrimental. So if you really learn to use 4WD properly on snowy pavement, you'll be constantly shifting to 4WD on most accelerations and 2WD on every turn. Which is a PIA so almost nobody does this. 4WD Auto doesn't need to "see" the road, it only needs to detect the rear wheels slipping during accelleration and that's the only thing it should react to. Anything else is detrimental.

It's not a major leap of faith when an automatic system transitions between 2WD and 4WD quicker and more accurately than 99.999% of drivers.
 

word302

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I think that only holds true if it actually falls short. If it lasts as long as anyone is going to use it, it would be fine. Does anyone really know if it is prone to failure prior to the rest of the vehicle falling apart?

That's not to say you're wrong. I would generally agree, the clutch-based system would probably fail before a chain, but maybe neither would fail before the rest of the vehicle rusted away.
No I'm sure it will be fine for most users, but for the type of wheeling I do I need the most robust hard parts that I can get.
 

word302

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I am wondering where anybody got the idea that the "full time" transfer case doesn't use a chain drive? There is still a chain that transfers the power to the front driveshaft. The difference is the addition of an electronically controlled clutch pack that engages that chain based on feedback from wheel speed sensors. It is still a fairly standard part time transfer case and most definitely uses a chain.
The point is that you are adding a wear item to the inside of the TC. How fast that wear item fails is yet to be determined.
 
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The topic of Auto 4X4 is kinda like the old days when people did not want fuel injection. LOL Carbs were the only way to go. LOL A properly working auto 4X4 is amazing. It will perform circles around non auto units in adverse conditions. Some think they can out think the computer. HAHA. Kind of like ABS brakes. Light years ahead of conventional brakes. Of course there are instances where "locked up" is an advantage, but that is in a very small arena.

My 02.

Sam
 
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