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Easy to Understand - Jeep 4WD Systems

Rock Trac
Pete Trasborg
| Brand Manager, Jp
Posted December 18, 2007
Photographers: Jeep Corp.

Ending The Transfer Case Confusion

Quadra-Hydra-Trac II, Selec-a-Rock, Commando-Drive II ... Many of us have issues trying to keep all the Jeep four-wheel drive systems straight. What system came in which Jeep has been the subject of quite a few campfire arguments.

Well, we weren't even going to broach the subject until we got a nifty little brochure from Jeep Corporation that explains each one of the six current four-wheel drive systems, their features, and what vehicles they came in. So we took it upon ourselves to study the 120-page brochure and provide everyone with an easy-to-understand synopsis of the systems.

The base Jeep 4WD system has remained virtually unchanged since 1988. Sure, there were high pinions here and there, with vacuum disconnects, C-clips, and non C-clips, but we are talking about the bigger picture.

In the Wrangler, the Command-Trac system is based on a Dana 30 solid front axle, a choice of automatic or manual transmission, an NV231 (formerly NP231) transfer case, and a Dana 35 rear axle (with a Dana 44 optional over the years). Also optional for the rear axle is a Trac-Loc, which is a limited slip differential.

This is a part-time four-wheel drive system that is intended to be used as needed. With its new (for the time) shift-on-the-fly ability, this system was something to look at.

The Command-Trac is also available in the Liberty, but it's a different system.

The front axle is still called a Dana 30, but it is an independent suspension version of the 30, with an aluminum centersection. This isn't swappable with the solid axle Dana 30 and is prone to explosion when beat on with larger-than-stock tires. The NV231 remains essentially the same, and out back the Dana 35 is tossed out in favor of a Corporate 8.25 axle. There is no Dana 44 option for the Liberty, but Trac-Loc is still an option.

This is the other available system for the Wrangler that made a big splash with the introduction of the Rubicon Wrangler and, later, the Rubicon Unlimited. It features a 4:1 reduction in the transfer case and Tru-Lok locking differentials. The transfer case's 4:1 low range enables more control in technical off-road situations. The low-pressure, air-locked Tru-Lok differentials allow the driver to lock the front and rear axles from a switch on the dashboard, a first for Jeep vehicles.

Rock-Trac includes a Dana 44 front solid axle with a Tru-Lok locking differential and 4.10 gears, choice of an automatic or manual transmission, a heavy-duty transfer case (comparable to some pickup trucks with the only difference being a 4:1 low range), and a rear Dana 44 solid axle with 4.10 gears and Tru-Lok locking differential.

While both front and rear differentials are called Tru-Lok, only the rear functions as a limited slip when not in the locked position.

It's available in the Liberty (and will be in the '07 Wrangler), but the only thing that was included in our 120-page guide about this system was that it was the typical Command-Trac system.

That means it has two-wheel drive, four-wheel drive, and low-range four-wheel drive options. The low range is 2.72:1.

After some researching on the Jeep Web site, we were able to trick it into specifying a vehicle with this four-wheel drive system. The main thing that this system gives you over the NV231 is a heavier-duty transfer case. It's the same case that comes in the Rubicon Wrangler without the 4:1 low range. This includes a heavier-duty transfer case, which will outlive the Libby's front axle by a ratio of 5:1 (that's five exploded aluminum Dana 30s for every NV241 you could kill).

The transfer case is important because it includes a larger chain that will resist stretching longer than the NV231 chain. Also, it's a heavier case that is less likely to blow apart in extreme shock load kind of conditions.

The trick is how to get this system. There are limited ordering options to get the better power splitter. You've got three options for the '06 model year that can yield a good transfer case: the base sport model with Package B, the 3.7L V-6, and a six-speed manual or the Renegade Model with the 3.7L V-6, six speed manual, and either Package D or Package X. You'll find the NV241 under the Command-Trac HD part-time 4WD system. If you are left with shopping the '05 model year, there are four options; the three listed above, plus the Sport with the Package A, the 3.7L V-8, and the six-speed manual trans.

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