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

aldo98229

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I have Selec-Trac + LSD on my JL Sahara: in winter driving conditions, this Sahara is superior to any of the many JK Rubicons I owned before.
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Thanks for the mention. I 2nd that, Off-Road Plus is not for winter driving.

4WD Auto is better for winter pavement than 4WD. The reason is that 4WD locks 1 front tire and 1 rear tire at the same rotation speed. In turns, none of the tires will travel the same distance so 1 tire will be forced to skid (when it otherwise wouldn't) and lose its lateral traction holding you in the turn. This is why it's common to see 4WD vehicles skidding off the road in turns. The 4WD drivetrain will force one tire to skid regardless of whether power is applied or not and you suddenly have only 3 tires holding you to the turn. Of course, front and/or rear lockers also force the same tire skidding.

4WD Auto will not force a front and rear tire to turn at the same speed. Therefore, you can hold turns at a faster speed in 4WD Auto than 4WD HI. It is almost but not quite as good as AWD on winter pavement. AWD allows splitting power between front and rear 0-100%, 4WD Auto only splits power 100% rear or 50/50 front & rear.
I would get use out of it with the patchy slush and ice i get here. I just have to not think about any potential issues with the durability of the rock-trac or the cv's. To be fair, I haven't read anything negative for either one so it's probably safe to assume they can still handle tough crawling.
 

AcesandEights

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When I had a TJ I really wished it had the Selec-Trac that I had in my XJ. There is a difference between all-wheel/full-time and 4H, and that difference made the Selec-Trac a better t-case for winter driving. The torque split is different.

I don't know if the full-time Rock-Trac, or whatever it is called, has a similar torque split as the old Selec-Trac, but if it does, then it isn't the same as 4H, and it will provide enough differentiation between front and rear to allow it to perform better on-road than trying to throw it into and out of 4H. It's just better than a locked t-case (front/rear) for winter driving (heavy rain, hail, snow, etc.). Having had both, I really appreciated the differences.

I did not however choose to purchase the full-time t-case in my new Rubicon and that is because it isn't chain driven (that's my understanding anyway), and I don't plan to use my new Rubicon in the same way I used my XJ. I have a 4Runner that I can drive in inclement weather, with "auto" full-time 4x4.
 

word302

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I like it simple because it gives me every option. I like having control off road, and with the system I still have access to 4 hi and 4 lo.

But, there are times, like when driving through some of the crappy mixed weather that the northeast presents, that I don’t want to have to hop back and forth between 4 hi and 2 hi.

It’s also nice for when my wife drives since she doesn’t want to have to select the correct mode for the correct situation. Same goes for my a soon to be driver in the house.

My two cents, for what it’s worth, is it gives you more options and doesn’t take away from any capability.
I’d argue that a clutch-based system will never be as strong as a gear/chain-driven system, so while it doesn’t necessarily take away capability it does in fact fall short on strength and durability.
 

AcesandEights

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I’d argue that a clutch-based system will never be as strong as a gear/chain-driven system, so while it doesn’t necessarily take away capability it does in fact fall short on strength and durability.
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.
 

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I’d argue that a clutch-based system will never be as strong as a gear/chain-driven system, so while it doesn’t necessarily take away capability it does in fact fall short on strength and durability.
It's proving difficult to find actual info on the t-cases outside of the standard Rock-Trac. I did find a forum comment that RT FT uses clutches in 4A and mechanically engages in 4Hi and 4Lo, but no reference material.

Would make since (at least for low) because the gear reduction takes place ahead of the power take off.
 

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I would get use out of it with the patchy slush and ice i get here. I just have to not think about any potential issues with the durability of the rock-trac or the cv's. To be fair, I haven't read anything negative for either one so it's probably safe to assume they can still handle tough crawling.
CV joints are actually more durable than U joints. The reason why people don't like them on Jeeps is because:
  1. The CV boots are susceptible to being torn by sticks & roots. Once dirt gets inside the CV boot it gets destroyed fairly quickly. So a torn CV boot must be repaired ASAP.
  2. CV joints are very difficult to fix on-trail whereas a U joint is easier to repair, at least to a "limp home" state.
  3. CV joints are more expensive to repair.
So a rock crawler who expects to break a joint on occasion will absolutely want U joints, even though they are not as durable. People who wheel over sticks and roots often will have added anxiety over tearing a boot.
 

AcesandEights

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Maybe this is a circular argument/reasoning, but unless you break a u-joint, what's the difference? If the CV is more durable (which I'm not saying it is or isn't), but you never break a u-joint, then the u-joint serves you well. The maintenance and replacement of the CV is more expensive and more likely (in my experience), because most of us are more like to tear a CV-boot than break a u-joint, and then the cost of the CV comes into play, regardless of which is more durable. Unless you're breaking either one, the u-joint is better; and if you are breaking u-joints it's easier to replace anyway (and limp home), which is better anyway.

I've never broken a u-joint, but I've replaced three CV-joints due to torn boots (due to loss of grease and introduction of water and dirt).
 

Reinen

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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.
I've been curious about this myself and looked into this. The JL 4WD Auto clutch is the front driveshaft itself. It is significantly thicker. I haven't found details about how it actually works. I assume it has a mechanical "locked" mode for 4WD HI and a "clutch" mode for 4WD AUTO. The transfer case would disengage the driveshaft for 2WD. So it may be that even if the 4WD Auto clutch fails it could still lock for 4WD HI.

If anyone has more info about this I'd love to hear it.
 

oceanblue2019

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CV joints are actually more durable than U joints. The reason why people don't like them on Jeeps is because:
  1. The CV boots are susceptible to being torn by sticks & roots. Once dirt gets inside the CV boot it gets destroyed fairly quickly. So a torn CV boot must be repaired ASAP.
  2. CV joints are very difficult to fix on-trail whereas a U joint is easier to repair, at least to a "limp home" state.
  3. CV joints are more expensive to repair.
So a rock crawler who expects to break a joint on occasion will absolutely want U joints, even though they are not as durable. People who wheel over sticks and roots often will have added anxiety over tearing a boot.
The Jeep JL's CV's have an issue with breaking especially on slick rocks. I have personally been involved in a MOAB recovery which snapped a CV as well as involved with a Sahara with a similar failure. Both were on factory sized tires as well.

I have yet to see someone break a U-joint even with big tires and lots of gas pedal abuse. In those cases it's the axle splines going into the carrier that twist or snap.

I have personally broken the FAD twice; once axle/collar; second occurrence was the other axle broke at the FAD collar (while engaged).

The RCV's are awesome but they are very different in design and material used from the factory CV's and no comparison should be assumed. The RCV's are the ultimate as they give you the smooth running of a CV but also great strength and a reliable boot as well. Plus they are orange.

I am not sure what they have done on the 392 as I would assume it would be munching CV's rapidly. But we are not hearing this..... Would be interesting to get one on some slick rocks where you need to use some throttle to heat up and get traction and what happens when it grips. That is where I've seen the factory CV's fail.

Also the select-track is not available on the diesel which is curious.
 

Zandcwhite

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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.
I’m assuming the new case is similar to the np242 from the xj days. The 4 auto used a clutch type engagement, but the planetary, 4 hi, and 4lo as well as the actual connection were all identical to a standard np231 chain drive and all. That being said, the 242 is the only tcase I’ve actually blown up on the trail. More moving parts mean more potential failure points in my opinion. As far as cv strength, I hope the new ones are stronger than the old xj Dana 30 front cv’s as those failed on every trail I ever took them on. The factory u-joint shafts in the Dana 30’s were way stronger than the factory cv shafts.
 
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Reinen

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I've never broken a u-joint, but I've replaced three CV-joints due to torn boots (due to loss of grease and introduction of water and dirt).
Exactly. If you don't tear your CV boots the CV joint is more durable. But CV boots aren't all that hard to tear. I have 4WD Auto and CVs. The boots are rather well protected from rocks but a stick can definitely find its way in there and tear the boot if you're not so lucky.

Luckily for me, sticks and roots aren't all that common in the Utah desert. But snow is.
 

AcesandEights

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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.
 

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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.
 

Reinen

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The Jeep JL's CV's have an issue with breaking especially on slick rocks. I have personally been involved in a MOAB recovery which snapped a CV as well as involved with a Sahara with a similar failure. Both were on factory sized tires as well.
Do you mean slick rocks or slickrock? Because dry Moab slickrock is anything but slick and will wrench the heck out of your drivetrain. You have to expect a high chance of breaking something there. It's worse than using 4WD on pavement. That's the rock crawler who wouldn't want CVs.
 
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