Part 4: A Ton Of Axle Fun
Six years ago we bought, built, and thrashed a ’75 Chevy K-10 for our Ultimate Adventure in the Midwest. After years of neglect and parts pilfering, we are bringing it back to life, and a better future.
The truck’s previous axles were one of its coolest highlights. As such, they were also among the first components pillaged for other projects. The front high-pinion Dynatrac Pro-Rock Dana 60 was arguably the single most valuable part of the truck. The stout rear full-floating Chevy 14-bolt was customized by Off Road Unlimited with disc brakes and other good stuff.
Budgets are different now. We’re sold on the do-it-right-the-first-time reliability of 1-ton axles for the K10, though, and investigated the highest-value way to pull it off. Junkyard axles are the most cost-effective, but only if you have the skills to freshen them up. We explored the next step up: military surplus axles.
The military uses various fullsize Detroit Three trucks as commercial utility cargo vehicles (CUCVs). GM was the supplier in the ’80s, so replacement CUCV crate axles—Dana 60 fronts and Chevy 14-bolt rears—still have decent availability. Specs called for 4.56 gears (good for our intended tire size and gearing), a rear Detroit Locker, and an optional front Trac-Lok.
On the 2010 Ultimate Adventure, Chris Durham of Chris Durham Motorsports talked about CUCV axles and their advantages for our Ultimate K10’s rebirth. He offered to remanufacture some junkyard axles basically to CUCV spec, but with a few upgrades. Here are some notes.
Dana 60 front: This is a direct bolt-in. Durham upgraded the hubs to premium Warn units. The previous Dynatrac Pro-Rock 60 had a Detroit Locker, but this version is going to be slightly more road-biased. Durham installed an ARB Air Locker for on-demand traction when needed but open-diff steering the rest of the time. For improved cooling through increased oil capacity and better heat dissipation, a finned diff cover got the nod.
Chevy 14-bolt rear: If we were building a machine only for off-road, a 72-inch-wide dualie 14-bolt would get serious consideration. But for simplicity and streetability (no flares or mudflaps required here), the 69-inch CUCV 14-bolt suits us just fine. Durham freshened up a 1-ton/full-floater 14-bolt with a Detroit Locker and custom disc brakes. (The 3⁄4-ton semifloating 14-bolt is less desirable and isn’t an easy disc-brake candidate.) A Mag-Hytec rear cover is an insurance-providing splurge. This premium cast-aluminum unit provides extra oil capacity, cooling fins, a magnetic drain plug, and an O-ring seal.
14-bolt rear discs are a topic of debate. Some GM experts, including Henrik Hairapetian at GM Truck Center and Stephen Watson at Offroad Design, feel that the OE drums are fine for most applications. Hairapetian’s one exception is mud trucks that need constant cleanup. Watson adds, “The stock [1-ton] drums are most likely going to be way too much brake for the back of this truck, so you’ll probably want to turn them down with a dial-adjustable proportioning valve.”
We like discs for the maintenance advantages, because water-induced brake fade is eliminated, and for the approximately 50-pound weight savings. Plus, we had the proper master cylinder and proportioning valve left over from the previous 14-bolt.
So, Durham used aftermarket caliper mounts (available from Chris Durham Motorsports) and frontend rotors and calipers on the 14-bolt. One issue is the lack of a mechanical parking brake for street use. A possible solution is to use Eldorado calipers, which have built-in parking brakes, and order custom aftermarket cables. GM Truck Center recommends the transfer-case disc setup from High Angle Driveline (www.highangledriveline.com). Hydraulic line locks are another secondary-brake option, but these systems are not DOT-compliant.
Chris Durham shipped the assembled axles to GM Truck Center, where the GM experts swapped them in. First, the placeholder front springs were replaced with Superlift 4-inch-lift units. A Superlift 4-inch K10 kit has been on the market since about the time our ’75 1⁄2-ton rolled off the assembly line.
We’re following the lower-lift trend, using less spring arch and more fender-trimming. This improves ride and handling by lowering the vehicle’s center of gravity compared to the traditional 6-8 inches of lift required to clear 37s with no other modifications. GM Truck Center swapped in its own spring plates and even custom-bent rear 9⁄16-inch outside-diameter U-bolts for the rearend.
Our Ultimate K10 is now ready to roll—to the bodyshop.
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