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Driveshaft and Gearbox Upgrades - Big-Truck Tech

Posted in How To on July 1, 2001
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Here’s what you get with the Klune-V Extreme Underdrive. The basic coffee-can–sized unit has the shift pod attached and is ready to bolt in. The output spud shaft is available in different spline counts for many different applications, and the input spline arrangement  has just as many options. Two adapter mount plates and a cable shifter complete the package—all for around $1,895. Try to get lower transfer case gears and axle gears for that small chunk of change. Plus, you now have options available for gearing selections. Here’s what you get with the Klune-V Extreme Underdrive. The basic coffee-can–sized unit has the shift pod attached and is ready to bolt in. The output spud shaft is available in different spline counts for many different applications, and the input spline arrangement has just as many options. Two adapter mount plates and a cable shifter complete the package—all for around $1,895. Try to get lower transfer case gears and axle gears for that small chunk of change. Plus, you now have options available for gearing selections.
The CNC-machined Klune-V Extreme Underdrive is a beautiful piece, good enough for your coffee table. Check out the five different mounting options on the input side of the unit. Klune offers two basic styles: the David model with 4:1 gearing made for rockcrawling, and the Goliath model with a 2.7:1 ratio for heavy-duty applications such as our mud-lovin’ truck. The CNC-machined Klune-V Extreme Underdrive is a beautiful piece, good enough for your coffee table. Check out the five different mounting options on the input side of the unit. Klune offers two basic styles: the David model with 4:1 gearing made for rockcrawling, and the Goliath model with a 2.7:1 ratio for heavy-duty applications such as our mud-lovin’ truck.
Our friends at Tri-County Gear first pulled out the stock transfer case of the Super Duty and started measuring up for the Extreme Underdrive to be installed. This rig sits about 3 feet off the ground, so no lift hoist was even needed. Our friends at Tri-County Gear first pulled out the stock transfer case of the Super Duty and started measuring up for the Extreme Underdrive to be installed. This rig sits about 3 feet off the ground, so no lift hoist was even needed.
Since the mount for this installation was on the transmission, Tri-County Gear used the optional mount plate to further support the weight of the transfer case. Note the various indexing holes to allow for nonstandard installation locations. This is what we needed to lower the front output of the transfer case. Even with the drop-down ability of the different clocking positions, some crossmember mods were needed. Since the mount for this installation was on the transmission, Tri-County Gear used the optional mount plate to further support the weight of the transfer case. Note the various indexing holes to allow for nonstandard installation locations. This is what we needed to lower the front output of the transfer case. Even with the drop-down ability of the different clocking positions, some crossmember mods were needed.
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The crossmember, which supports the transmission and transfer case, drops low to clear the front driveshaft. By moving the transfer case rearward using the Klune-V, the front driveshaft angle would be lessened for better service life. However, moving it back also meant it would interfere with the crossmember, which would have to be modified. The front adapter ring is sealed to the unit on both sides to eliminate leakage. Older Extreme-Duty models had all-thread holding the case together and acting as mounting bolts, while the new versions easily bolt into place. The crossmember, which supports the transmission and transfer case, drops low to clear the front driveshaft. By moving the transfer case rearward using the Klune-V, the front driveshaft angle would be lessened for better service life. However, moving it back also meant it would interfere with the crossmember, which would have to be modified. The front adapter ring is sealed to the unit on both sides to eliminate leakage. Older Extreme-Duty models had all-thread holding the case together and acting as mounting bolts, while the new versions easily bolt into place.
With everything bolted up, it was felt that an additional support crossmember would be the best idea since this truck is used for mud whumpin’. The stock crossmember and mount were retained, and an additional support was fabbed to mount to the rear Klune-V bracket. With everything bolted up, it was felt that an additional support crossmember would be the best idea since this truck is used for mud whumpin’. The stock crossmember and mount were retained, and an additional support was fabbed to mount to the rear Klune-V bracket.
While mocking up the assembly before final installation, measurements were made to see how far the transfer case needed to be dropped. With the best position decided for front driveshaft clearance, the transfer case still had 36 inches of ground clearance at its lowest point. We figured that’s plenty good for this rig since it is mainly for mud. Just in case the truck ever got rock friendly, the stock skidplate was retained for further protection. While mocking up the assembly before final installation, measurements were made to see how far the transfer case needed to be dropped. With the best position decided for front driveshaft clearance, the transfer case still had 36 inches of ground clearance at its lowest point. We figured that’s plenty good for this rig since it is mainly for mud. Just in case the truck ever got rock friendly, the stock skidplate was retained for further protection.
Custom fabbing at its finest was done on the crossmember by building a bridge or hoop where the driveshaft would need to go. All working angles were checked and considered, and the stock crossmember was torched away for clearance with the fabbed-in hoop strengthening it. If you don’t have a clue about bending loads and structural rigidity, leave this process to the professionals. Custom fabbing at its finest was done on the crossmember by building a bridge or hoop where the driveshaft would need to go. All working angles were checked and considered, and the stock crossmember was torched away for clearance with the fabbed-in hoop strengthening it. If you don’t have a clue about bending loads and structural rigidity, leave this process to the professionals.
The final step is to fill the Klune-V with ATF oil, slap on the front driveshaft, and spray some nice black paint on the bare metal. The result is a nice driveshaft angle, lower gears with a selection of various ratios, and one mean truck. We wouldn’t have it any other way. The final step is to fill the Klune-V with ATF oil, slap on the front driveshaft, and spray some nice black paint on the bare metal. The result is a nice driveshaft angle, lower gears with a selection of various ratios, and one mean truck. We wouldn’t have it any other way.

It’s like a good recipe: Take one big Super Duty, add equal parts big lift and big tires, stir in some shop time, and let cool. Then go ’wheeling. If you follow directions and cook it right, you have a killer rig that can perform. But if you don’t pay attention to the whole recipe, you’ve just cooked up disaster.

As it turns out, big lifts and tires on big trucks aren’t just bolt-on propositions. Sure, the lift kit fits and those 44-inch tires look way cool, but even after you’ve regeared the axle with the lowest cogs, you still don’t have enough grunt to get out of your own way, even in low range. Worse yet, the front driveshaft keeps spitting out CV joints because of the poor operating angles, and you just blew out your third axleshaft from banzai maneuvers in the mud. What’s a guy to do?

In this type of scenario the first thing to do is to keep in mind what the truck is for. Is it a trailer queen (not likely), a rock buggy (hardly), or a real mud whumper? For our case this truck may look spiffy, but it also does weekend duty at the local mud hole, where Dana 60 front stub shafts are eaten for lunch. However, its biggest problem was keeping the front driveshaft alive. Oh yeah, more gearing sure wouldn’t hurt either.

After scratching some heads and throwing some ideas around, Jason Bunch at Tri-County Gear in Pomona, California, came up with the solution long favored in rockcrawling circles. Rockcrawling? How could that radical technology help a mud truck? The answer was surprisingly simple as soon as the “oh yeah, more gearing sure wouldn’t hurt” was bandied about.

Deeper gears for the axles are fine, and this truck already sports low-geared Dana 60s front and rear. But that means more work on both ends of the truck, which results in sacrificing the highway top speed, and is why this solution didn’t come up first. Besides, it was the driveshaft that caused problems, and changing axle gearing wouldn’t help that at all. The simple and easy way to eliminate these concerns was to install a Klune-V Extreme Underdrive gearbox, a longtime standard of rockcrawling and trail-riding aficionados. Since this trick unit mounts between the transmission and transfer case, the high range of the rig is not affected unless the box is engaged. It’s similar to a two-speed rear axle, but it’s mounted in front of the transfer case, so you affect whatever position the transfer case is in. The extra length of the unit also moves the transfer case rearward, helping to alleviate some of the front driveshaft angle problems. But the best reward is the fact that the Klune-V has multiple clocking positions on each end of the unit, which allows the transfer case to be rotated to virtually any angle imaginable. This means that, unlike the stock position, the front output of the transfer case can be lowered for optimum driveshaft angle.

While simply bolting a Klune-V unit in place and driving away is entirely possible on some rigs, the added length requires driveshaft lengthening in the front and shortening in the rear for most vehicles. In addition, crossmember modifications are usually needed, and the shifter needs to be mounted inside the cab. For this install we chose the Goliath model, which features a 2.7:1 low ratio, more than enough for this truck, and super strong to boot. Check out how this Super Duty was saved by the addition of a Klune-V and now romps freely in the mud, destined to break more front axle parts.

Sources

Tri-County Gear
909-623-3373
http://www.tricountygear.com

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