If you've been paying attention, you know we're building a 1975 1/2-ton Chevy to tackle the 2005 Ultimate Adventure. In year's past we've built some impressive late-model rigs to take on our annual off-road road trip. But rather than try to outdo last year's trick Tacoma, we wanted to find a wreck we could transform into a machine that will drive across the nation, wheel, and make it back in mostly one piece.
This month we're focusing on the most abused parts of any 4x4, the axles. From experience we know that this is one place you don't want to skimp on when you're building for extreme use. We knew there was no way the original Dana 44 and 12-bolt were going to survive our trip with 39-inch tires, lockers, and 5.13 gears. We needed 1-ton axles. Sure, we could have tracked down a Dana 60 front out of a '77-'91 GM 1-ton for around $1,500. But we didn't, and here's why: The newest GM 60 we could hope to find is going to be at least 14 years old. It'll only come with a low-pinion centersection. And assuming it's not bent or has spun a pinion bearing, it'll still need to be completely rebuilt and regeared for another $2,000. Even after we built it up with all the trick parts we ended up using, it still wouldn't be wide enough to run the bead-lock wheels we had planned. So we knew a custom axle was in the cards.
 For a 4x4 that's sole purpose...  For a 4x4 that's sole purpose in life is to conquer the toughest trails in the country, we needed more axle than the stock Dana 44 or even a junkyard Dana 60 could give us - a lot more. To get there we started with a Pro-Rock Dana 60 centersection from Dynatrac. Designed specifically for off-road use, the Pro-Rock casting is contoured for maximum ground clearance, and engineered to be significantly stronger than any Dana version. Add to that the high-pinion design that not only improves ring-and-pinion strength, but also gives you a much better driveshaft angle and it's not even a fair comparison. |  Using Dynatrac's detailed...  Using Dynatrac's detailed order form, we were able to spec out a complete high-pinion Pro-Rock assembly with a driver-side differential, 31 1/2-inch leaf spring spacing, and a width of 74 1/2 inches to work with our Hutchinson bead-lock wheels. After the tubes were cut to length and machined to the proper diameter, the end forgings were pressed on and welded in place. The two tubes were then joined with the centersection to form the housing in Dynatrac's horizontal press. |  Next our housing was set up...  Next our housing was set up in the mill to machine the spring pad and drill and tap a series of six 5/8-inch holes directly into the casting. Two of the holes will be used to attach the spring plate, and the other four will be used to mount our ram-assist steering cylinder. |
Since the frontend was going to be an all-new piece, we wanted to save some money on the rearend and run a 14-bolt. Plus it would give us a chance to try the new 14-bolt ARB Air Locker. To match the front axle width we had planned, we needed the widest 14-bolt axle we could find. Ideally we would have used a '91-and-up dualie axle (72 inches) but we had to settle for a 69-inch-wide version from a '78 GMC 1-ton van. We shipped a core axle we pulled out of the local boneyard over to the guys at Off Road Unlimited and stood back as they worked their magic.
 After a thorough cleaning...  After a thorough cleaning the housing went back to the welding station to have the tubes rosette welded to the centersection. The housing dimensions were then verified one last time before the passenger-side spring pad was welded on. In hindsight, we should have had Dynatrac weld the lower shock mounts on too, but we didn't know where we wanted them, so we'll have to do it ourselves now. |  A GM Dana 60 front axle uses...  A GM Dana 60 front axle uses 11/2-inch 35-spline inner shafts (left), and 1.31-inch 30-spline outer shafts with 1480-sized steering U-joints. Strong stuff to be sure, but on a truck that's going to weigh close to 6,000 pounds when it hits the trail, we needed to upgrade. Since we were going to require custom axleshafts anyway (for our 5-inch-wider axle), we stepped up to Dynatrac's competition series 35-spline inner and outer shafts. These chromoly gems are built by Superior Axle to Dynatrac's exacting standards for spline pitch, length, and seal surface finish. Extra material is added to the yokes to support CTM 300M U-joints, and the entire shaft (including the yoke) is heat-treated. |  We'd never run a set of chromoly...  We'd never run a set of chromoly shafts with standard U-joints. That combination is just asking for trouble because if the joint breaks it'll wipe out the shaft too. A set of CTM Racing 300M joints proved indestructible in our Ultimate Avalanche, so we weren't going to run anything else in our new truck. Thanks to the CTM's larger cross and pin diameter they have more strength for high-stress applications like ours. The CTM joints also eliminate the failure-prone needle bearings and replace them with a bronze sleeve. In our experience the sleeves show very little wear when greased regularly. |