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<-Note links: Klune-V References on Special Applications to left.

 The "Klune-V Applications Manual" contains tech info on aspects of Klune applications, such as adapters needed or not as well as driveline geometry.

Shortest Klune / T-case Combo: Klune-V Bronco Dana 20 Combo 

[Shorter than stock Wrangler T-case replacement]

Klune/Atlas system

An Extreme Underdrive is an underdrive gearbox that bolts in place between the transmission and transfer case. we call it "extreme," because the underdrive multiplies your existing gear reduction by up to 4 times, rather than a usual underdrive of 1.2 times, or so. It is intended for extreme four-wheel-drive applications, rather than towing or gear splitting in a big truck. It works equally well with both manual and automatic transmissions.  

The David crawler is intended primarily for short wheelbase applications where extreme low-crawl gears are desired for moving very slowly and precisely through difficult or very tight rock formations, and up or down waterfall-type obstacles. The emphasis is on precision, skill and finesse. While plenty stout, it is geared too low to be practical for hammer-down, tire-spin applications. (If you need more tire speed, simply shift the David into 1:1 ratio, leaving your transfer case in low range).  

On the other hand, the Goliath is intended for full-size, high-power hill climbing, mud boggin' pulling and tire spinning. Strength and unstoppability are the emphasis.  

Both units are physically the same size, and have the same bolt pattern. These units are new-manufactured, purpose-built units, which come with a full one-year warranty. While similar to "dual transfer case" units in function, they are not built up from cut or sectioned used transfer cases.  

You're a serious enthusiast, which means you've gone down the road and know what you want. You've probably beefed up your suspension, expanded to 33-inches or larger tires, and added a locker or two. You're having fun, you're moving over the environment in all its forms and challenges. There's just one more step to go to maximize your  rig ­ extremely low gearing for extreme high adventure. With the Extreme Underdrive you've gone high tech and really low gearing. How low can you go?

Bottom line, you'll be able to crawl up obstacles that previously were viewed as insurmountable. Here's a real-world example from our R&D department with Greg "Go-for-it" Miller behind the wheel. Here's the scene.

"We're tracking in twelve vehicles looking for action in Surprise Canyon. We run into a Close Encounter of the Watery Kind, seven waterfalls that by the old book would require winches to conquer. We took on three of them just for the fun of it. That's the point, isn't it? Loose rock, slippery rock, big rocks, moon rocks ­ we'll take them all on. Course, we had an edge. First we let the non-Extreme Underdrive vehicles have a go at it. One, a Jeep did manage one of the seven waterfalls, although he did get sideways and take several passes to make it  across. The other guys without Extreme Underdrive packages said let's break out the winches. Not us in the Toyota Mini Truck and the 1977 Bronco equipped with the Extreme Underdrive upgrade. Both rigs crawled up three waterfalls totally unassisted and without any thrashing. Talk about a trial by fire ­ rather water!

And you still get to keep your existing low range, and good highway gears.

So You Can Crawl Over New Horizons ­ What Else Does the Extreme Underdrive Offer?

How about saving wear and tear?

How about saving money?

Extremely Low Gearing Means Reduced Body Damage and Mechanical Breakage.

Time to stop or turn before that rock bites your quarter panel.

By going slower, you control what you hit and how hard you hit it.

Reduces shock loads on axles, drive train and suspension.

Torque can be applied more smoothly, thereby less clutch stress.

Simple physics that pay off in reduced repair, expenses and less down time.  

What are the alternatives?

Sure, you can go another route to get low gearing. But they're called compromises for very good reasons.

You can:

Change axle gearing to real low gears.

Pro: You can get some lower gearing

Con: You have to turn a zillion RPM at highway speeds. Not a good thing.

You can:

Install a two-speed T-case with deeper gearing.

Pro: It gets you somewhat lower and keeps highway driveability.

Con: Loss of normal low range. And no super crawling.  

What are the numbers?

The Klune-V Extreme Underdrive's multiple low range provides the most versatile gearing set-up available.

If your vehicle is fitted with the "Goliath" Extreme Underdrive, you receive three different Transfer Case ranges:

• Normal High Range

• Normal Low Range

• An additional "crawl" range ­ 2.7 TIMES AS LOW AS YOUR EXISTING LOW RANGE

If your vehicle is fitted with the "David" Extreme Underdrive, you receive four different Transfer Case ranges:

• Normal High Range

• Low Range

• A 4.0 Crawl Range

• Plus an EXTREME crawl range FOUR TIMES AS LOW AS YOUR EXISTING LOW RANGE! (for those super technical spots you want to really creep through)

The Extreme Underdrive provides the most flexible set of options  available to respond to the wide range of environmental challenges you'll meet.

It also means you can actually use your off-roader on the road to get to the off-road site.

For example: Say you have a stock Jeep with stock tires. It turns about 2700 RPM at 65 MPH. With 33s and 4.11 axles (or 35s and 4.56 axles), still close to stock and fairly civilized. You will maintain decent highway operation. But if you switch to 4.88 or deeper gears, the highway ride heads toward the unpleasant zone. Worse yet, these super deep-cut gears rely on a relatively small and thereby much weaker pinion gear.

Sand or mud driving usually requires high range or normal low range gearing. If you are missing your normal low range, a result of switching to a lower geared T-case, you'll find yourself stuck, literally, with an unsatisfactory choice of either high range (not deep enough) or a too-deep low range which restricts your tire RPM and as a result fails to pull you clear.  

Normal low range (about 20-30 to one ratio) tends to work best for scaling loose hills. Scrambling helps maintain the momentum to keep forward-ascending motion. On the other hand, hard, technical rock crawling will be best enjoyed, and accomplished, using much deeper gears. If you venture onto "Sledgehammer" type trails, you¹d probably opt for a setting 130-225:1. Less than that and you'd be reaching speeds too fast for optimal control.  

"It's no surprise that we found a ratio of 145-225:1 best suited to keep you smoothly moving over the rocks and crawling up the falls. That's on the way up. Gravity wanted to drag us down; the Extreme Underdrive took us over the top. On the return trip, we got the best control from the 60-130:1 range. Now gravity tries to throw you down the mountain. Go too low, and you won't be able to scoot if you need to correct a potential end-do situation. Extreme Underdrive Super Crawling made it a walk on the wild side but with total control.

"So we had the water world experience in the canyon environment, and we looked for another dimension. Someone said Moab. They've got slick rock that gila monsters can't even hold onto. We blasted up Interstate 15 to Utah, then left it for some ledge climbing. Walking the ledge keeps you on your toes and the edges of your treads. The slick ledge rock responded best to 60:1 for climbing; slow enough for control, but enough momentum to get up the ledges you can't straight crawl up. Going down, we opted for 145:1 as you kind of "lowered" yourself down ledges, still keeping control.

"During transitions between more challenged sections, like on easier trails, we selected standard low range or 4.0:1 for best results. Extreme crawl is too low. Too many RPM, too much buzzing.

"Final summary: For serious Technical Rock, go for at least a 130:1 final drive."

You're an experienced off-roader. You can walk the walk, dance the dance, but now it's time to learn to crawl ­ Extreme Crawl. The traditional off-road driving method called "Off-road Dancing" involves coordinated tap-dancing on the brakes, clutch and gas pedal to wrangle your way through the tough spots. Good tricks of the sport and valuable survival skills, but it's time to enroll in Extreme Underdrive School for the latest n super crawl driving techniques.

Some trail or rock conditions require a measure of tire spin to negotiate, especially mud. Use Normal Low Range or High Range. This is not a crawl application.

With the Extreme Underdrive at your control, conditions that once only responded to brute momentum as the only way up, are now "no problem." Without relying on sheer momentum and the resultant speed, you also lessen the chances of breakage or going off the line or losing it altogether. No more need to hang right at the edge that momentum requires to carry you up to the top.

In the past, as in pre-Extreme Underdrive days, the reason you couldn't hang on without momentum was because you were already going too fast. Here's the logic. The surface of a rock is very slick, maybe wet, maybe uneven, too. As you move across it, the weight of your vehicle will shift from tire to tire as it compensates. If you are moving fast, the truck will experience a lurching motion which can be sufficient to yank the tire loose from the rock. With the slower speeds afforded by the Extreme Underdrive, the rig does not lurch, and the harsh jerking motions are eliminated. Traction is maintained and you keep on going.

"While climbing a waterfall at another major event, the trail leader (an experienced wheeler, and one who knew the trail cold), told me, 'You can't crawl this waterfall. You absolutely must use momentum.' He didn't know I had the Extreme Underdrive installed or if he did he didn't think I could make the climb. I asked if I could just give it a try anyway. 'Okay,' he said, 'but be prepared to back down.' So, I started up, very slowly, and kept going until about three-quarters up at which point the tires started slipping. The trail leader shook his head, 'Okay, now you gotta back down and get us some momentum.' I called back, 'Just a sec'.' I used another technique called 'Hunting for traction.'

"You get the tire RPM down to almost nothing, as in one RPM. Turn the wheel a bit to the left, and the rig slowly walks that way. Then turn the wheel a bit to the right, and the rig walks in that direction. With this method, you can get one of your tires to grab a small section of ridge, then start moving again. Conversely, if your tires were spinning any faster, the inertia involved in trying to get the entire truck moving again would simply tear the tire loose from its toe-hold. My Bronco got climbing again, and made it all the way to the top without any further traction problems. This clearly illustrates that there's a whole new kind of driving out there once you have this level of low gearing at your disposal."  

Prior to deep gearing now available through the Extreme Underdrive, you pretty much had to go the stick route, especially if you were into traversing technical rock. That choice was dictated by the fact that with a manual transmission you would have at your disposal much lower first gear ratios which naturally gave you increased hold-back going downhill. At the other end of the stick, so to speak, with an automatic transmission, you had some problems. When you were climbing one side of a boulder, you were consequently slipping the converter in order to build torque. Torque is good. Torque is required. But then at the top of your climb, you'd find yourself suddenly accelerating if you didn't exercise coordinated and precise control over the throttle and brake. It's a simple matter of control, and with a stick tranny you got more.

For loose hill climbs, sand, and deep mud, the distinct preference was towards an automatic transmission. With a stick you are required to carefully pick the right gearing before you started into the particular environment. You couldn¹t afford to lose tire speed even in a relatively quick shift. With an automatic, you simply stick it into drive, put your foot into it, and the transmission picks the right gear. A no-brainer, which means more time to focus your attention on where you¹re going.  

So there were pros and cons on both sides of the picture of auto vs. stick, and a compromise either way you approached the matter. Not so any longer. With the Extreme Underdrive upgrade, stick or automatic has become a question of simple personal preference. With 100-plus gearing, it is now possible to crawl down the steepest hill with your foot off the brake and the tires turning about 2 RPM. Even with an automatic. You can set your hand throttle and crawl over Sledgehammer or Rubicon obstacles with your foot off the brake or gas, maintaining a constant speed ­ close as you can get to cruise control. With an automatic or a stick!

The "Goliath" 2.7 ratio box is intended to be used in high horsepower, full-size truck applications. the gearset has an input torque rating of 5500 ft/lbs. The strength limitation is apparently only the SIZE of the shaft you use to mate the unit to your transfer case. Different sizes are available to fit different transfer cases. We have NEVER (in 9 years of building these at this writing) had a gearset failure. The mating shaft is made of high strength case hardened 8620 alloy steel. They are about as tough as you can make them.

the David 4:1 gearset is rated at 2500 ft lbs input torque. The "David"'s  "low" position 4:1 ratio is intended for CRAWLING. It's "Hi" 1:1 position is intended for when you need tire speed, or are planning to thrash. In high range, it's strength is limited only by the size of the shafts used to mate to your transmission and transfer case. In low range, it's purpose it to go slow. These units are a proven reliable design with years of tough use in trail and competition vehicles. For example the Chevy pickup pictured below had a David in it, and was run successfully through he original 4XOR Ultimate Adventure, including "Die Trying" in Montrose.

"Go-for-it" Greg says, "I personally had an Extreme Underdrive "David" behind a fuel-injected 5.7L motor stuffed into a '77 Bronco. I've flogged it for over 40,000 miles, and we¹re talking flat-out, full-throttle hill climbs ­ sand ­ mud ­ low range wheel-hopping scrambles up soft sandstone and crumbling Moab ledges ­ California rock crawling ­ Interstate miles.

 The Extreme Underdrive eats it all up.

is also available, if you want to have the top of the line components and get the best of all. Kinda pricey, but awesome, This is what I use in my Grand Cherokee buildup