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Late-Model Transfer-Case Crawlers

Posted in How To on May 1, 2001
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Photographers: Craig Perronne
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Aluminum and chains. That’s all you think there is to know about late-model transfer case stuff, right? You’ve heard all the talk about chaindrives versus geardrives, aluminum housings versus cast-iron housings, and you know which is best, don’t you? That’s what we thought. This is going to be hard for a lot of you to swallow, but like it or not, the new transfer cases from New Venture Gear make its old New Process stuff look like an Atari 800 compared to a Play Station 2.

That’s right. Your NP205 was the ultimate transfer case back in 1969. But the most torque it ever had to deal with was 400 lb-ft put out by the Cummins turbodiesel in the ’93 Dodge W350. Sure, it has been used in modified trucks with twice as much torque, but a 1.96:1 low range is all the gear reduction you are going to get out of the stock case. Sorry, but 1.96:1 just isn’t enough for the kind of ’wheeling most of us like to do. Fast forward to today, and you can get an NVG271 or NVG273 in a Ford Super Duty that laughs at the 500 lb-ft of torque a Power Stroke puts out. The NVG271/273 weighs less than the NP205 and has a better 2.72:1 low range.

“But what about slip-yokes?” you ask. “All the new aluminum transfer cases come with slip-yokes.” You’re right, they all do now. Want to know why? Slip-yokes make assembling drivetrains easier (less expensive) for the manufacturer. By using a slip-yoke, two machining steps are eliminated from the output shaft of the transfer case, and the driveshaft can be slid into position on the assembly line without having to torque the four bolts that would hold the U-joint in place. Slip-yokes are not unique to chaindriven transfer cases; even the NP205 used slip-yokes in some ’80s GM applications. We agree that slip-yokes are wrong, but it was a design that came about independent of chaindrives or aluminum housings.

Finally let’s talk about material selection. Pound for pound, aluminum is just as stiff as steel, and magnesium is about 50 percent stiffer than both of them. Stiffness, however, does not equal strength. The stiffer a transfer case housing, the better it will support the spinning shafts, gears, and bearing inside when subjected to large amounts of torque. Engines with four- or six-bolt main bearing caps hold the crankshaft in position better than a two-bolt main bearing cap would for the same reason. If you want a transfer case that you can bash over rocks, then stick with cast iron because it will distort easier and be less likely to crack than aluminum or magnesium. If you shield the transfer case properly, bashing it on rocks won’t be anything to worry about.

Follow along with us now as we walk you through the current offerings in the transfer case world. Some of these cases would make great swaps into older iron in desperate need of better low-range gears. Some of you may just want to know what your new rig has underneath so you can brag about it when hanging out in the garage with your buddies.

Sources

Advance Adapters
Paso Robles, CA 93446
800-350-2223
www.advanceadapters.com
JB Conversions
Sulphur, LA 70664
337-625-2379
www.jbconversions.com

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