My '73 Chevy C30 Ramp Truck has led a hard life. It was converted to Ramp Truck status early on and has been hauling cars ever since. Last year we ditched the 454ci V8 gas engine and TH400 three-speed trans in favor of a compound-turbocharged Cummins 5.9L 12Valve diesel and 47RH four-speed with lockup converter transmission. Both the engine and transmission were modified by Powerdriven Diesel for towing duty and hot rod fun.
It didn't take long to destroy the stock Dana 70 rear axle. A couple of burnouts was really all that was required to send the spider gears in the differential crying to their mama. Determined the make lemonade out of this lemon, we contacted the folks at Quick Performance for an upgrade.
The team suggest using the axle out of a late-model Chevy truck, which originally was supplied to GM by American Axle & Manufacturing. The axle not only comes with disc brakes but also a larger 11.5-inch diameter ring gear, which dwarfs the Dana 70's 10.5 inch gear. Right out of the gate this is a better axle for the kind of abuse the Ramp Truck endures, but Quick Performance further improved it by swapping out the 3.73:1 ring and pinion gears for an ever higher 3.42:1 gear ratio. Our Cummins certainly would appreciate the lower rpm and higher wheel speed that this ratio would force it to operate in. The stock open differential was also replaced with a Detroit Trutrac limited-slip differential for two wheel peels!
Here's where things get even more exciting; the new axle came out of a single rear wheel truck. This meant that our stock 16-inch dually wheels wouldn't fit. Also, 17s wouldn't go on either. After many hours of trial and error fitment we stumbled upon a combination of 19.5 wheels and 1/4-inch spacers, which fit the truck and provided a more modern look. Check out the video to see how we made dually wheels fit a single wheel axle as well as tips for setting your pinion angle correctly.
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Finnegan' Garage Ep.66: Cummins-Powered Chevy Dually To Single Wheel Axle Swap!