1996 Chevrolet C/K 3500 Dualie Regeared Rearend - Gearing Up For The Long Haul

Going From 4.10s To 3.21 To Save Gas

The Sport Truck StaffAug 1, 2007
Photo 2/25
So, here is a question for all of you dualie owners with those custom wheels: What do you do now that you have shrunk the outside diameter of your tires well past the factory size-by so much, in fact, your truck is revving way too high just cruising on the highway? We have a '96 Chevy C/K 3500 Crew Cab dualie in the Sport Truck stable with this problem.
We bolted up a set of 19-inch Brentz wheels with 245/45R19 Pirelli tires. Well, the Pirelli's diameter is 3.4 inches smaller than the factory 255/75R16 that GM used. As cool as the new wheel and tire package makes the truck look, the increase in fuel consumption and wear on the motor is not.
There are a few options to cure the problem. We could swap out the transmission with a unit that has a taller Overdrive. We could install a secondary gear splitter, like a Gear Vendors unit, or we could change out the rearend gears. In our case, the truck already features a 4L60E AOD transmission that has a 0.070 Fourth gear ratio, which is pretty big, and a Gear Vendors unit will set us back 3 grand, so we'll focus on the rearend.
We contacted Yukon Gear & Axle for one of the company's 3.21 ring-and-pinion sets, along with an installation kit. The truck has a 4.10 already stuffed inside the housing, but that's all about to change. Because we're not experts on how to set up a rearend and so on, we contacted the crew at Unitrax to have them install and set up the gears, instead of us butchering the job. The complete cost of the job, including labor, parts, and oil, only set us back 900 bones and only took one day to complete. The new gear ratio will bring the tach down a few hundred rpm, which will keep our big-block alive much longer. It will also get our fuel consumption back in check, which is a major thing to think about with today's gas prices and a thirsty 454.
The Final Word
This story's Final Word should be called the Final Math Problem. Check out the math equation we put together to justify the gear swap.
By this math, you can see that we have a projected savings of 2,600 bucks and some change, which is not bad for a few parts and a day's worth of work.
Stock Vs. Regeared Rearend
STOCK GEAR RATIO 4.10
70 MHP CRUISING 2,800 rpm
FUEL ECONOMY 10.97 mpg
Money Saved Via Increased Fuel Economy
STOCK REAREND
10.97 x 33 gallons =
362.01 miles per tank of gas
REGEARED GEAR RATIO 3.21
70 MPH CRUISING 2,400 rpm
FUEL ECONOMY 11.43 mpg

REGEARED REAREND

11.43 x 33 gallons =
377.19 miles per tank of gas
Now There Is An Extra 15.18 Miles Per Tank Of Gas!15.18 miles x 52 fill-ups (average) per year = 789.36 miles 789.36 miles x 3.33 gallon (average price for 91 octane fuel) = $2,628.56 saved

Sources

Yukon Gear & Axle
Everett, WA 98204
888-905-5044
http://www.ringpinion.com
Unitrax
Anaheim, CA 92806
800-622-4327
www.gounitrax.com

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