2005 Ultimate Adventure Ultimate 1975 Chevy K10 Part 3

Ultimate K10, Part 1
Ultimate K10, Part 2
Ultimate K10, Part 3
Ultimate K10, Part 4

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.

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.

Lockers are mandatory front and rear for all vehicles that go on the Ultimate Adventure. But with all the street miles we have to tackle just getting to the trail, it's nice to be able to run open from time to time. The selectable ARB Air Locker has proven itself in past Ultimate Adventure truck buildups, so when we chose the Pro-Rock front axle for our K-10, we knew what locker would find its way inside. The gear techs at Dynatrac bolted our ARB in with a Motive Gear 5.13 high-pinion gearset and set a textbook pattern.

With the axleshafts, eight-lug Dynatrac wheel hubs, and brake kit installed, all we had to do was sling the front Pro-Rock axle under our truck. We've done this with three floor jacks and a few sore backs in the past, but the crew at GM Truck Center made it so much easier with a little help from a forklift. To make our installation super smooth we ordered Dynatrac's spring plate and U-bolt kit so we wouldn't have to track down these parts in a junkyard.

Since we were only planning to run a 4-inch Tuff Country suspension lift on the front of our truck, we knew we were going to have to make room for our crossover steering system. The rivets were air chiseled out of the original engine crossmember and then we had to cut it in half to remove it from between the framerails.

We bolted in this high-clearance crossmember from Missouri Off Road Outfitters that ties the two engine mounts together and leaves a lot more room for a drag link. Since we had the whole front clip off the truck anyway, we added Off Road Design's steering-box brace to triangulate the box to the front crossmember.

The rear 14-bolt axle for our UA K10 started life in a '78 GMC van. After we pulled it out of the junkyard we took it to Off Road Unlimited to have it rebuilt. First the housing was chemically stripped and the original spring pads were cut off. The pinion support was cleaned and the inside of the housing was painted and prepped for the all-new 14-bolt ARB Air Locker and a Motive Gear 5.13:1 ring-and-pinion.

Off Road Unlimited did a world-class job on the rear axle. The attention to detail would make some heart surgeons look sloppy. The inside of the housing was painted to facilitate oil drain-back and help seal the casting. The pinion support was then assembled with a new bearing and a 1410 yoke modified by ORU to use U-bolts instead of straps.

When ordering 5.13 gears for a 14-bolt axle with an ARB, make sure to specify a thick ring gear, as the ARB carrier is designed to use gears for the 4.10-and-down case. If you're familiar with ARB differentials, you'll notice the locking mechanism has been moved to the opposite side of the carrier to make room for the third pinion bearing in the 14-bolt design. When routing the air line, ORU makes sure that it doesn't rub against any internal surfaces.

Rebuilding the 13-inch drum brakes on a 1-ton axle is expensive, not to mention they weigh a ton. When it comes to shopping for disc-brake conversions for these axles, the most complete package on the market comes from Off Road Unlimited. Sure, some people can piece together a bracket and a caliper combo at home, but ORU goes beyond that and includes a rotor, new wheel studs, a brake-line kit, a master cylinder, and an application-specific proportioning valve.

The stock stamped-steel cover hit the Dumpster long ago, so we had ORU seal up our 14-bolt with its cast-aluminum cover. The Dana 60 version of this ORU cover survived our 2002 Ultimate Adventure, but since we plan to cut the lower lip off the axlehousing, we may go with a cast-iron piece for a bashproof setup.

For a truly bulletproof, street-legal, and maintenance-free bead-lock wheel, we chose a set of Hutchinson Rock Monster wheels. These high-end forged-aluminum wheels use an exclusive double bead-lock design that holds both inner and outer sidewalls in position. Twenty-four 1/2-inch studs hold the two wheel halves together while a tire-specific rubber ring locks the tire sidewall to the aluminum rims. They're not cheap, but for a truck like ours, these wheels are worth every penny. To seal the two wheel halves together, a special O-ring gets pressed into a machined groove on the wheel face. We coated the ring with some grease to keep it from sticking and then placed the wheel half into the rim shell and started the nuts on the eight long studs.

To match our street-legal bead locks, BFGoodrich brewed up a set of 39-inch DOT-legal Krawler tires. They practically got delivered to our offices in an armored car! They use the same tread pattern as the championship-winning competition Krawler, but are constructed with a harder rubber compound that will let us run them on the street. We slipped the Hutchinson inner rubber bead lock into the tire and then slid the inner wheel shell in through the backside of the tire.

While we were waiting for the axle hardware to be assembled, we were back at GM Truck Center shooting photos of this custom winch mount for the rear of our K10. Since we knew there were going to be times we needed the capacity of a 16,500-pound winch, but didn't want to hang the138 pounds off the front bumper, we mounted this Warn 16.5ti over the rear axle of the truck to pull us out of anything we can't drive through! Don't worry, we'll still put a winch in the front of the truck, but it'll only weigh 89 pounds.

As we're writing this, the Ultimate K10 is tucked away in the corner of Fabworx, custom metal fabricators, getting a four-point rollcage installed. Next month we'll show you how Fabworx built the cage and fitted our MasterCraft seats and Tuffy Security center console.

Ultimate K10, Part 1
Ultimate K10, Part 2
Ultimate K10, Part 3
Ultimate K10, Part 4