Finding a Rear Axle Ratio on a Chevy Silverado

Several methods are available to determine the axle ratio and type of carrier utilized in a 2002 Chevy Silverado. The higher the number assigned to the gear (e.g., .456, .411), the lower the gearing. This means that the engine has higher RPMs to every revolution of the the tire, and has more pulling power (i.e., at 40 mph, the engine could be cruising at 3,000 rpm). The downside to lower gearing is that the engine revs higher when cruising and you have lower top-end speed. Also, this causes higher gas consumption. Installing higher gearing (e.g., .273) affords less pulling power and acceleration. On the plus side, the engine rpm will be lowered, and the Silverado has higher top-end speed (can reach 70 mph at a lower rpm) and better gas mileage.

Step 1: Open the glove compartment to find the build sheet, which lists all the drivetrain components. It gives a description of the rear axle, whether it is a posi-traction, limited slip or open rear, and the axle ratio.

Step 2: Write down the vehicle identification number. It can be seen on the top of the dash through the driver's side of the front windshield. Call the dealer with the number and they will tell you the axle ratio.

Step 3: Raise the rear of the truck by placing the floor jack under the rear axle. Raise the truck so the rear tires are off the ground. Place the jack stands under the rear axle for support.

Step 4: Place a mark on the inside one of the rear tires on the tread straight down at the 6 o'clock position. Make a corresponding mark on the pavement directly under the tire mark. Place another mark on the driveshaft by the universal joint and a corresponding mark on the axle.

Step 5: Turn the tire one complete revolution while counting the number of turns the mark makes on the drive shaft. For example, if the mark on the driveshaft makes a little more than three revolutions to one complete turn of the tire, the gear ratio is a 3 series ratio. To get the exact final ratio measure the distance the driveshaft mark has moved past the mark on the housing. Measure the circumference of the driveshaft and divide by 4. For example, if the driveshaft turned over three revolutions, hold the three as a constant and add the final ratio using the quarter increments. A 10-inch round driveshaft divided by 4 gives you .25 for a quarter turn. If the driveshaft turned 3 ¾ turns to one revolution of the tire, the ratio is 3.75.