Exclusive: Behind The Scenes With Jeep's New Four-Door
One of the most anticipated new vehicles in the four-wheel-drive segment right now is the completely new 2007 Jeep Wrangler JK, which replaces the 10-year-old Wrangler TJ. Ever since Jeep teased us with its four-door Dakar concept in 1997, the idea of a four-door Wrangler has inspired Jeep enthusiasts everywhere. While we all knew a factory-built four-door was coming, few facts were known about the Unlimited, and Internet rumors ran rampant with speculation. We brought you some of the first JK two-door photos a couple of issues back, and we recently talked our way into an invitation to a secret warehouse in suburban Detroit, where Jeep allowed us unrestricted access to the '07 Wrangler Unlimited months before its unveiling, as well as a Q&A session with the team behind the JK program. It is good to have friends in high places.
Essentially identical to its two-door sibling from the B-pillar forward, the '07 Unlimited is the four-door model of the new Wrangler and the second body style based on the new JK platform. Three models of the Unlimited will be offered: the base X model, the sophisticated Sahara (distinguished by body-colored flares), and, of course, the mighty capable Rubicon, which is sure to give the Hummer H3 a run for its money in the dirt. Ranging in weight between 4,075 pounds (Wrangler X/manual) and 4,340 pounds (Rubicon/automatic), this four-door Wrangler is a full 20 inches longer-and about 200 pounds heftier-than the two-door Wrangler, which brings the wheelbase to a lengthy 116 inches, when compared with 103 inches for the outgoing, two-door TJ Unlimited and 95.4 inches for the two-door JK. The frame has been stiffened by 50 percent in torsional rigidity and 100 percent in bending resistance, while the body is about 50 percent stiffer when compared to the TJ. Approach and departure angles on the Unlimited Rubicon-44.4 and 40.5 degrees, respectively-are similar to the two-door (44.3/40.4), but the breakover angle drops down to 20.8 degrees from 25.4. Track width is the same as the two-door at 61.9 inches, compared to the 58.5-inch track of the TJ.
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Gone from the lineup is the anemic 2.4L I-4 (although a four-cylinder CRD diesel model will be available in Europe) as well as the venerable 4.0L I-6. Replacing both engines is the standard 3.8L OHV V-6 making 205 hp and 240 lb-ft of torque. This is the same V-6 found in Chrysler's minivans, but the JK is the first application where it is longitudinally mounted. Drive by wire replaces the mechanical throttle linkage of the TJ, allowing engineers to tailor throttle response to varying situations. Along with power and refinement, the new V-6 allowed Jeep to meet stringent crash and emissions requirements. To us, the engine bay appears big enough to fit a larger engine, but Jeep officials are mum on whether there will be future engine options for the JK in the U.S. Our gut instinct tells us there will be. Backing the new engines are the same four-speed (42RLE) automatic and six-speed (NSG 370, now with reverse lockout) manual found in the current TJ, each featuring stronger cases.
The standard transfer case is now the NV241 Command-Trac with a 2.72:1 low range, and of course the Rubicon will continue to feature the NV241OR Rock-Trac 4.0:1 case. This Gen 2 Rock-Trac is stiffer and quieter than the model it replaces, and neither case has a slip tailshaft, now favoring smoother-running CVs with a slip joint in the driveshaft. And all Wrangler JKs have a different ABS algorithm while operating in 4-Lo. The full range of safety acronyms are either available or standard on the JK, but fortunately, engineers tell us that the usually intrusive ESP system can be completely disabled at the push of a button.
As of press time, Jeep was still determining what to call the JK's upgraded Dana 44 axles, which are beefed up in so many areas that nothing is interchangeable with the TJ. This new axle, which we'll call a Dana 44 hybrid for now, has bigger axletubes, bearings, ring gear, and pinion stem; the Unlimited also gets a standard Dana 44 hybrid in the rear-30-spline for Sahara and X models, 32-spline for the Rubicon-while two-doors get a standard rear Dana 35 (30-spline). Front axles are either Dana 30 (27-spline) or a Dana 44 hybrid (30-spline). Rubicon models also get new electric lockers with magnetic activation instead of the pneumatic operating axles on the TJ. When the JK Rubicon lockers are disengaged, the diff is open, as opposed to the TJ Rubicon, which had a rear limited-slip. Other models can be upgraded to a Trac-Lok limited-slip in the rear. Rubicons and automatics have 4.10:1 gears stuffed in their axles, while everything else gets 3.21:1s standard with 4.10:1s optional.