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Dynatrac Free Spin Hub Conversion Kit - 6.7L Upgrades That Won't Void Your Warranty

Part 4: Front Axle Upgrade For Better Fuel Economy

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The last time around, we added a larger, slightly heavier wheel and tire combo and lost a little more than 1 mpg. Granted, with the 6.7L's whacked-out emissions system that dumps raw fuel into the engine on the exhaust stroke to burn the soot from the DPF, who's to say what the real mileage numbers could be? But despite the capricious and fuel-wasting antics of our vehicle's active regenerations, our test data is what it is.

One of the things we've never been too fond of in Cummins-powered 4x4 Dodge trucks since '94 is the absence of locking hubs on the front axle. Worse still, is the fact that the factory wheel bearing assemblies place the wheel bearings very close together, increasing leverage loads and hastening bearing wear if heavy hauling or big tires are involved.

Dynatrac's Free-Spin kit addresses these shortcomings with an exquisitely machined spindle that bolts to the factory '94 to '02 Dana 60 or '03 to '09 AAM steering knuckle to accommodate a 1 -inch 35-spline stub shaft, hub assembly, and locking hub dial for true two-wheel-drive operation. In addition to the added strength of the 35-spline stub shaft, the Dynatrac hubs space the inner and outer wheel bearings farther apart, decreasing the effects of leverage to increase bearing life. Furthermore, the wheel bearings in the Free-Spin kit are serviceable. Unlike the factory unit bearings, you can pull the Free-Spin bearings out to inspect, clean, and repack them with grease, as well as adjust the bearing preload. They're long-lived units that will take all the punishment these trucks can throw at them.

Although it's a relatively straightforward installation that most guys with moderate wrenching skills can handle, we took the easy route and headed down to TAG Motorsports in Escondido, California, to have our Free-Spin kit installed by shop foreman, Jay Miller. Miller and the rest of the gang at TAG have a lot of experience in wrenching on diesel trucks and had our Dodge ready to roll without any hiccups.

With the kit installed, we were pretty surprised to find a noticeable difference in steering feel. Given that unlocking the hubs stops the axleshafts, ring and pinion, front driveshaft, and front transfer case output shaft from spinning, it stands to reason that omitting all that rotational mass is bound to have a positive effect on noise, vibration, and harshness (NVH) quality. And as you can see, the elimination in drag resulted in a very definite increase in fuel economy. Come on by next time when we'll be tossing a Fitch Fuel Catalyst into the equation.

The Mileage Report
Here's the running tally for each installment of this series. Mileage numbers are generated on the same 250- mile mixed freeway and city street circuit and are hand-calculated by noting miles driven and fuel used from the same pump at the same fuel station. Numbers are the average of at least three test circuits.

STOCK:
15.55 mpg
S&B cold-air intake:
16.31 mpg
S&B cold-air intake, Snugtop Xtra Vision shell:
17.30 mpg
S&B cold-air intake, Snugtop Xtra Vision shell, Toyo Open Country A/T tires:
16.20 mpg
S&B cold-air intake, Snugtop Xtra Vision shell, Toyo Open Country A/T tires, Dynatrac Free-Spin hub conversion:
17.13 mpg
Hidden Benefit To Date:
1.58 mpg

SOURCES
Dynatrac TAG Motorsports
8-00/-928-1766
tagmotorsports.com
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