Advance Adapters RubiCrawler: Ultimate Crawl Ratios for Jeep TJ and JK Wrangler with the 42RLE Transmission
This tour of the RubiCrawler with Steve Roberts at Advance Adapters explains the function and fit of the Rubicrawler. The ingenious gearbox occupies the factory tailhousing space on the Jeep TJ and JK Wrangler models equipped with the 42RLE automatic transmission. Without driveline modifications, this is a “bolt-in” swap with immediate and significant gearing advantages for big tires and the OE or aftermarket axle gearing.
In the rocks, many Jeep owners want crawl-pace gear ratios to reduce the risk of vehicle damage and powertrain load. By crawling slowly, we can negotiate rough, rocky terrain with better vehicle control. This minimizes wheel spin while delivering exceptional torque.
The more elaborate methods of gear reduction have involved dual-transfer case installations. Bulky, weighty and requiring chassis and driveline modifications, adding an extra transfer case is a complex approach. For some, simply installing lower ratio, low-range gearing in the transfer case has been popular—but this does not offer the same range of ratios that an extra gearbox does.
Advance Adapters has provided an ideal solution for owners of 2003-present Jeep Wrangler and Jeep Wrangler Rubicon models equipped with the 42RLE automatic transmission. A “RubiCrawler” gearbox, essentially a two-speed planetary transmission, offers direct drive plus 2.72:1 reduction drive. The gearbox fits neatly between the transmission and transfer case, offering the driver a dramatic reduction ratio by simply moving levers.
In addition to the Jeep’s original low-range ratio, the RubiCrawler provides an additional reduction that takes gearing down another 2.72:1! This means that the stock Jeep Rubicon low range reduction of 4:1 (NV241 Rock-Trac transfer case) can be multiplied to: 4 x 2.72 = 10.88:1!
How to Properly Shift a Rubicrawler Gearbox
Shifting from high range to low range plus low range of the RubiCrawler, the reduction nearly triples. With the transmission’s 1st gear ratio of 2.84:1, the Rubicon model’s 4:1 low range, the RubiCrawler’s 2.72:1 ratio and a final axle ratio of 4.10:1, the total reduction available is 127:1! Add to this the torque converter multiplication, and the torque available in the lowest gear slots is astounding!
The RubiCrawler is well conceived. Advance Adapters RubiCrawler system, with either the twin-stick option or a universal style shifter, looks like a factory installation. Actually, the shifter components and fit-up pieces have an even more durable presence than original equipment. Better yet, the RubiCrawler fits the exact length and space of the stock transmission-to-transfer case adapter. This means no driveshaft cutting, mounting issues or driveline problems. Install the assembly by the instruction sheet and start enjoying an additional 2.72:1 reduction ratio!
Note: For current pricing and additional details, visit the RubiCrawler page at the Advance Adapters website catalog. The instruction sheets for various RubiCrawler applications are available at the Advance Adapters website.
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