It can be argued that there's no bigger bang-for-the-buck performance upgrade than new axle gears. Auto manufacturers are tasked with building a vehicle that is optimized for both highway efficiency, comfort, and performance. Because of this, there's going to be a trade-off of some sort. All too often, manufacturers lean toward efficiency over performance. Add to the mix the fact that most enthusiasts add larger tires at some point, which effectively raises the gear ratio, and it's easy to see where changing the gearset can make a big difference.
Using our 2002 Chevrolet Silverado 2500HD project as an example, the truck came from the factory with 3.73:1 axle gears. When we increased the tire size from factory to 37-inch tires, we effectively raised the gear ratio (numerically lower) by about 20 percent. It would be as if we installed 3.23:1 axle gears. The result of this is more difficult acceleration but lower engine rpm at highway speeds.
To get the engine back in its proper powerband and regain the lost acceleration, we needed to change the axle gears to a lower (numerically higher) gearset. To get the truck back to relative normal, we would have needed to install 4.30:1 gears. However, because we did a six-speed transmission conversion, and to get a big of added performance, we opted to go even lower to 4.56:1 gears.
For this project we turned to the gear and axle experts at Yukon Gear. We ordered up a ring and pinion set, master install kit, the company's Dura Grip limited-slip differential, and 4340 chromoly axle shafts. We opted for the Dura Grip limited-slip over a locking differential for its improved highway manners. The Dura Grip is fully rebuildable and features 4320 chromoly spider gears, Raybestos composite clutches, and a strong four-pinion design.
Even though the GM 14-bolt axle is one of the easiest to set up gears in, we opted to leave this important job to the professionals and headed over to South Bay Truck & 4x4 in Hawthorn, California. Owner Frank Gilliland has installed thousands of gearsets during his career, leaving us no doubt that he'd get ours done right the first time. The job requires special tools and knowledge to avoid a frustrating situation and potential damage. Frank has the rear axle set up in just a few short hours. The front differential of these IFS Chevy HD trucks is another project altogether and one that we'll address in the next installment.