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teralow 3.07 for Isuzu

By Dr. Sean Michael

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When Isuzu released the venerable Trooper to America it jolted the growing SUV market. The boxy, utilitarian 4x4 that comfortably hauled 5 passengers plus all of their gear was long on value. In the process of its evolution, the truck soon garnered the most votes for three years as Motor Trend's 4x4 of the Year. It did that not only by being rugged and economical, but by striking a balance in its design. The IFS provided good on-road handling, while trading off some of a solid axle's trail potential. Accordingly, its gearing was chosen to pass easily between service in both types of jungles- asphalt and dirt.

First gear in the manual transmissions was typically 3.77:1 (in comparison to the Jeep WranglerTJ's current 4.04:1), while axle ratios in Troopers, Rodeos and other models were either 4.10, 4.30, 4.56 or, in a few vehicles, even 4.77s. While these ratios are certainly respectable, their potential was limited through the use of 2.05:1 transfer case low range (compare this to a TJ's 2.72:1). The result was a crawl ratio, at best, of 37:1.


While most owners of Isuzu 4x4's would find 1st gear and 4Lo to be plenty capable, most owners, as with any SUV's, are not trail enthusiasts. So it was the pioneering individuals in the Isuzu OHV community who sought solutions to the problem of too much speed and too little control while on the trail. A few people swapped engines and transmissions via the now defunct Advance Adapters kit for 4.3L Vortec motors. Many sought out the hard-to-find 4.77 axle gears that came with option code SL2, the so-called Big Tire Package (31x10.5" and honeycomb aluminum rims). A rare few went so far as to swap in Toyota front axles and transfer cases equipped with Marlin Crawlers.

All of these solutions worked fine for the enterprising souls who put themselves on the bleeding edge of innovation. However, the average 4x4 enthusiast (if there is such a person) is not interested in such one-off, expensive experiments. As with any marketplace, such unmet demand drives businesses to get busy and come up with solutions. For the Isuzu aftermarket, this happened in 2000 when Tera Manufacturing (Utah) stepped up to the plate by putting the first ever aftermarket low range gear set for Isuzu's into R&D. The process saw the first prototype installed at the end of the year and production units shipped the following autumn.

Isusu Applications
Fits 1987*-1992 All models. Transfer case uses a rear, slip-yoke style driveshaft.

Fits all models 1993-1996.Transfer case uses a fixed-yoke rear driveshaft.

Fits 1997-2001 with automatic transmissions only.

Fits 1997-2001 with 5-speed manual transmissions only.

First Encounter
My first encounter with the teralow 3.07 gear set (other than the enormous clamor generated by the online Isuzu communities!) was at the Moab 'ZuZoo IV in May of 2001. At this event, the largest off-road gathering of Isuzus in the Americas, were four vehicles that had been equipped with Tera's new 3.07:1 gears in their transfer cases.

Watching those rigs slowly pick and choose their lines was apparently all one had to see to know that this was THE mod to get. I listened with growing interest to trail reports from those envious onlookers who watched one or more of the Tera-equipped rigs. Soon it was my turn to gawk.

I followed Fernando Rivero on the Moab Rim trail in his Amigo, which served as the test mule for the prototype gears, for a day. On obstacles where I was putting the WomBAT's Lock Right and ARB Air Locker to full use, along with the umph of its tweaked 3.4L Camaro V6, Fernando was able to slowly and nimbly ooooze his way up, only occasionally relying on his own ARB. Yes, he was an excellent driver. Yes, his Amigo was a lot lighter, but those gears!

I wasted no time falling in behind Fernando's Amigo. Not long after doing so, I weaseled my way into its driver's seat. With the WomBAT in the rear view, I got my first taste of the control and capability that Tera's gears afford. It was immediately apparent that the 3.07:1 ratio yielded a gear reduction that felt like a full gear lower than stock. In sharing this impression over the CB, I soon found out that his Amigo was only sporting 4.56 axle gears. I was used to 4.77s! Correction: Make that more like two full gears lower!

Throughout the remainder of 'ZuZoo I was able to watch and talk with the other Tera owners. All of these were Amigos or Rodeos, and none were manual transmissions. Upon my return, I immediately began looking into the prospect of installing the gears in the WomBAT. I had come away with feeling that the gears rivaled, if not exceeded, the benefits of the rear ARB Air Locker that had for so long been considered the single best off-roading modification available for our trucks. Fortunately, Jeff Mock and the rest of the crew at Tera again stepped up to the plate and provided a set of the 3.07's to review.

The gear set arrived in an extremely well-protected bed of dense foam, with each element fitting snuggly into its pre-cut slot. Accompanying the three-piece kit (new idler gear, low speed clutch drive and shift rail) were a set of clearly-typed instructions and the ever important "Tera Inside" sticker, whose Intel mocking even a Mac guy like me could appreciate. The two pages of instructions offer a step-by-step description of the assembly and disassembly, coupled with an exploded view of the transfer case from the Isuzu factory manual. Following several discussions with colleagues who were running the Tera gears, I opted to take the whole shooting match to our local transmission specialist (aptly named Transmission Specialists).




Tera Manufacturing, Inc.
(801) 256-9897
8385 S. Allen St., Unit 115
Sandy, UT 84070
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