For years we've begged the engineers at Jeep to offer a three-speed transfer case.
The 4:1 Rock-Trac T-case is great and all, but really only in the rocks or through technical sections. It's pretty much worthless in the mud and sand where more wheelspeed is needed. Several aftermarket options have been available for many years; however all of them have required extensive modifications and new driveshafts, until now. The people at Advance Adapters did their homework and discovered that the tailhousing in the 42RLE automatic transmission found in '03-'09 Wranglers is simply an empty case. With a little ingenuity a heavy-duty six-pinion 2.72:1 low-range planetary gearbox was stuffed into this dead wasted space between the transmission and stock transfer case. The RubiCrawler was born. The result is a compact bolt-in gearbox that allows more gearing versatility than the stock 4:1 found in Rubicons and the necessary double-deep gearing that the non-Rubicon models require for the rocks. It's a win-win for everybody.
How's It Work?
Since the install, our RubiCrawler-equipped '07 Wrangler Rubicon has crawled the Rubicon Trail, revved through the Pismo sand dunes, and commuted several thousand miles on the highway. It shifts smoothly and easily and doesn't make any unusual noises. If you can shift the stock transfer case, you can easily shift the RubiCrawler without issue.
In the rocks, the stock 4:1 low-range transfer case gearing compounded with the RubiCrawler's 2.72:1 provides a whopping 10.88:1 low range ratio. On paper it seems like way too much, but it turned out to be extremely helpful in really tight situations where it helped us avoid body damage. The slower speed provided better throttle control and less bobbing over the rough stuff.
In the dunes we found the RubiCrawler's 2.72:1 way more useful than the factory 4:1 low range. We could blast up dunes in 4Hi with the RubiCrawler engaged and the rear locker on. We also liked running the 2.72:1 RubiCrawler with the T-case in 2Hi and the rear locker on. In the past the Jeep would sort of bog in High range or simply over-rev in Low. The RubiCrawler puts the gearing in the middle for optimum performance. Overall, the addition of the RubiCrawler makes the Wrangler Rubicon more versatile and perform better in every terrain.
Support the transmission so...
Support the transmission so you can remove the skidplates and crossmember. We used an Advance Adapters Uni-Raise universal drivetrain jack to keep everything in place. The driveshafts, breather hose, and T-case shift linkage need to be removed before unbolting the transfer case. Don't forget to unplug the sensor wires too. Wire the driveshafts up out of the way.
With the transfer case pulled...
With the transfer case pulled you can get to the empty transmission tailhousing and factory spud shaft. The tailhousing simply unbolts from the transmission, but you'll need a slide hammer with a 10x1.5mm adapter or bolt to pull the spud shaft. Anywhere from 2-4 quarts of tranny fluid will spill out, so be ready to catch it with a drain pan.
The RubiCrawler (right) replaces...
The RubiCrawler (right) replaces the factory tailhousing (left). Since the RubiCrawler is exactly the same length (about 7 inches) there are no driveline or crossmember modifications needed. There is no cutting, no welding and no grinding. It's a bolt-on deal.
The RubiCrawler is sealed...
The RubiCrawler is sealed to the transmission with RTV. It shares lubrication with the transmission so don't forget to add fresh Chrysler ATF+4 fluid when you are done. Check the fluid again after a short drive to make sure you added enough. The original transfer case simply bolts up to the RubiCrawler just like stock.
The optional electronic interface...
The optional electronic interface module (PN 42R800) plugs into the factory Jeep wiring harness. It allows the use of the Rubicon lockers and sway bar disconnect with the RubiCrawler engaged, regardless of what range the factory T-case is in. For mud and sand you can run the 2.72 low-range of the RubiCrawler with the lockers on, or run the rear locker only while in two-wheel drive for high-speed sand running.
The stock single transfer...
The stock single transfer case shifter is replaced with a twin shifter and a cable-actuated assembly which is mounted under the center console panel. Removing the driver seat speeds up the install. The new shifters poke neat and clean through the original T-case shifter slot without cutting up the body metal.