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The drive axle serial number located on the forward side of the right axle tube. The 2 or 3 letter prefix in the serial number identifies the drive axle gear ratio.
¦10.5 Inch Rear Axle-10.5 inch 25 Series Silverado¦8.5 Inch & 9.5 Inch Axles-¦8.6 Inch Rear Axle¦9.75 Inch Axles
GM CORPORATE 10-BOLTThis 10-bolt, with a larger 8 1/2-inch ring gear diameter, replaced the Dana 44 that was used in the front of some pre-1977 GMs. It can also be found in the back of 1983-91 1/2-tons and in the front of 1983-87 1/2-tons.
GM CORPORATE 12-BOLTThe stronger 12-bolt, with an 8 7/8-inch-diameter ring gear, can be found in various 1964-82 GM 1/2- and 3/4-ton rearends.
GM CORPORATE 14-BOLT The "small" GM 14-bolt has a 9 1/2-inch ring gear diameter. It was used in the rear of 1964-and-later GM pickups, and in the rear of 1984-91 3/4-ton Suburbans.
GM CORPORATE 14-BOLTWith a 10 1/2-inch-diameter ring gear, the biggest 14-bolt GM rearend looks much like a Dana 70, and is but a few thousandths of an inch shorter in ring gear diameter. This axle is commonly used with big engines and/or overly large tires. It was used under 1973-87 3/4-tons.