One of the best bragging rights of fullsize 4x4s is the freedom to go completely nuts with the drivetrain without having to worry too much about running out of rear driveshaft. We've heard of people stacking SM420 trannies, a few homegrown transfer case matings, and Offroad Designs' Doubler dual-transfer case setup. But we couldn't contain ourselves when we heard that Klune-V was developing a crawler box for fullsizes, so we scooted over to their facility and checked out what was in the works.
What exactly is a crawler box? In the case of the Klune-V box, it's a round aluminum housing that holds a planetary gearset-similar to those used in NP241 transfer cases. The box is available with a 2.72:1 or a 4:1 ratio.
The real beauty of this box is that it fits between the transmission and transfer case. As a result, it can be used in two-wheel drive and four-wheel drive, and you now have two different low ranges and a great double low (your transfer case low-range times the crawler-box low range). This location also means that you won't have to move the transmission or its shifter, although you'll need to move the 'case, modify its shifter, build a new crossmember, possibly lengthen the speedo cable, and alter both driveshaft lengths. The crawler box is only 611/42 inches long, but depending on what adapters are needed to fit in your application, it may not lengthen the drivetrain any.
What vehicles does it fit? It was originally designed for Jeeps (naturally) with Dana 300 and NP231 transfer cases. However, it can be adapted to fit nearly anything. Klune-V currently offers adapters to fit the crawler box to GM NP205s and NP203s. It doesn't need an adapter to bolt to a Dana 300, NP231, NP241, Ford NP205, NP207, or NP208. Also, '80-and-newer GM NP205s don't require an adapter. The company is also working on adapters for Dodges using the earlier transfer cases, Suzuki Samurais, and Pinzgauers. If you don't have any of these 'cases, call the company; it may be developing what you need or it may be able to build something custom for your application.
How's it work? Beautifully. Klune-V outfitted a '76 GMC with an SM465 and NP205 transfer case just before the 4-Wheel & Off-Road Ultimate Adventure ("Ultimate Adventure," Feb. 2000), which gave us a great opportunity to test the crawler box on- and off-road in some of the most abusive scenarios we could have asked for.
When we were flying down the highway, we didn't know the box was there. The engine rpm was the same as before we had the box and the speedometer wasn't affected. To engage the crawler box, we needed the vehicle to be stopped (you can shift when moving a little, but why unnecessarily risk damage?). The planetary is engaged by pulling a lever inside the cab. If we needed extra pulling power on pavement or low-range off-road but didn't want front-axle bind, we left the transfer case in 2-Hi and shifted the box into low. If we wanted the stock four-wheel-drive low-range, we shifted the box out and engaged the 'case in 4-Lo. And for extra-low, we engaged the 'case in 4-Lo and brought in the box.
With 4.56 axle gears, we had a crawl ratio of 58.54:1 without the crawler box, which we felt was plenty. With the 2.72:1 box, we have a 159.23:1 ratio and can now attest to how much this helps when rockcrawling. We didn't do much fussing with the clutch pedal before, but we don't touch it at all off-road with the crawler box. It gives us plenty of control over the vehicle because of the reduced speed and improved traction. Plus, the box didn't commit us to this final ratio; we could shift through the four-speed, and engage the transfer case and the box for nearly any combination and final drive ratio we wanted up to 159.23:1. By the end of the Adventure, we had logged over 2,000 miles (including the drive back to Los Angeles) and four ultra-tough trails. We had shifted the crawler box in and out about 40 times with no signs of wear and tear. That's only a sampling of what we think the box will stand up to, but that's all we've logged so far.