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Test Drive
Automatic Transmission
The results of the lower transfer gears were dramatic. Shifting into low range was like shifting into an entirely different vehicle. The first thing I noticed was that the Jeep started creeping forward even though I had my foot on the brake pedal. I had to use extra pressure to keep it stopped. Clearly, the torque had improved dramatically. Letting off the brake and increasing the throttle was a strange sensation. The rpms rose quickly but the Jeep's speed remained unusually slow. It was a somewhat disorienting feeling. The improved detent pockets in the shifter rod were also noticable. The shifting felt crisper than with the stock case.
With the stock gearing, I usually shifted into 1st gear, low range when I was driving over technical terrain. 2nd and Drive were too high and usually left for cruising to the next obstacle. Not so with the 4:1 gears. I found myself staying out of 1st over most of the obstacles unless I really needed to go SLOW. The Tera kit made all of the transmission's gears more useful when in low range.
Crawling over boulder-strewn sections was less jarring because I didn't have to use the throttle to climb over large rocks. Idle provided enough torque to crawl over rocks without requiring any additional throttle. That meant I didn't have to brake after coming off of the bigger rocks, too. This smoother performance on the rocks will translate into longer lifespans for the Jeep's parts.
Low gears provide slow speeds which
avoid situations like this where the driver
used too much throttle.
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It is this low speed torque that is the main reason why I think the 4:1 kit is so valuable even in an automatic transmission. Auto trannies have become very popular in the rock crawling community because they allow you to go extremely slow without worrying about stalling the engine. However, when attempting an obstacle that provides a lot of resistance, such as when your tires are up against a vertical rock face, you will need a lot of torque to overcome it. Applying more throttle will usually work but not always. If the obstacle requires a lot of engine rpm before the torque converter can turn the wheels, the vehicle might shoot up and over the obstacle or break traction. In the latter case, you can't get past the obstacle. In the former case, the sudden speed could catch you off guard and slam you into the next obstacle.
A few years ago on the Shoestring Trail in Washington, I saw a Grand Cherokee caught in a similar situation. He had caught a diff on a tree root while climbing up a dusty trail. The driver was trying to back off the root but it was providing a lot of resistance. The Grand Cherokee's torque converter couldn't overcome the root's grip so the driver continued to increase the engine rpm. Once the torque converter had enough speed to catch and break free from the root, the high rpms send the Grand Cherokee flying backwards into a tree. If the driver had lower gears, he would've had enough torque to turn his wheels without needing so much engine speed.
The only situations I encountered where the gears were not an improvement were those that required lots of wheel speed. If your primary interest is in racing up sand dunes or mud bogging, you will see little benefit from lower transfer case gearing.
Manual Transmission
Although the 4:1 kit is a great benefit to an automatic transmission 4x4, it's even more beneficial to a manual transmission 4x4. For starters, most manual transmissions have a first gear which is almost twice as low as an auto transmission's. Secondly, the final gear ratio remains constant whether you're accelerating or engine braking. As an example, if Project YJ had a manual transmission with a modest 3.83:1 first gear (used in the AX-15 5-spd manual which is used in most YJs and all TJs), the final gear ratio would be:
3.83 x 4.00 x 4.10 = 62.8
With low transfer case gears, manual transmission vehicles
can idle down these kinds of obstacles without using the brakes
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Now, as much as I like my automatic transmission, I have to admit a certain amount of envy for that kind of gearing. With a ratio that low, idling down scary slopes is within the realm of possibility. Being able to idle at 62.8:1 while negotiating your way around, over and between boulders gives you a tremendous advantage over someone else who has to worry about the engine stalling. The slow speed also gives you more time to react since the obstacles come at you much more slowly.
The slow speed also improves your traction by reducing the chances that you'll break your tires loose from the terrain. It is a fact that slowly turning tires are less likely to spin. That's the reason why sometimes a driver who has stalled his 4x4 on a steep obstacle will leave it in first, low-range and try to drive out by keying the starter motor. I've seen this technique work several times. With the 4:1 kit, you won't need to rely on your starter for that slow speed. And for those times when the 4:1 gearing isn't slow enough, you can still fall back on the starter motor technique with the added benefit that the lower gearing will put less stress on the motor.
Conclusion
The TeraLow gear set is one of those rare upgrades that improves your vehicle's offroad abilities by an order of magnitude without affecting its highway manners in any way. Given that Project YJ's prime objective is to competently straddle the worlds of day-to-day commuting and hardcore offroading, it's obvious why we consider the TeraLow kit to be one of the most important upgrades we've made to Project YJ.
Special thanks to Jason Conover for performing the installation.
...lars
Addendum
August 18, 2000
I've put on quite a few more kilometres since the installation and am still overwhelmed by how much better Project YJ performs off-road. Fourwheeling over highly technical terrain has become even more enjoyable now that I have more time to plot my next move. The lower gearing also lets me feel for traction at the slow, creepy-crawly speeds. If you're serious about rockcrawling, you should start setting some money aside for a TeraLow kit!
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