The General Motors 12 bolt axle was used in GMC and Chevrolet pickups from 1964 to 1982. It is a semi floating rear axle with a 8.875" ring gear. Its most notable weakness is the fact that it uses C clips to hold the axle shafts in place, but this can be remedied by an aftermarket C clip eliminator kit. The 12 bolt is a 1/2 ton to 3/4 ton axle and is comfortably rated for up to 35" tall tires on the highway. A passenger car version of the axle was offer produced, but not covered in the scope of the following information.
GM 12 Bolt Specs
| Applications | 1964 - 1982 Chevrolet & GMC 1/2 ton to 3/4 ton trucks |
| Full/Semi Float | Semi floating rear axle |
| Ring Gear | 8.875" |
| Axle Spline Count | 30 spline |
| Axle Tube Diameter | 3.00" |
| Pinion Diameter | 1.625" |
| Pinion Spline | 30 spline |
| U Joints | 1310 series |
| Ratios | 2.50 - 4.56 : 1 |
| Carrier Break | 2.50 - 2.76 | 3.42 -4.56 |
| Identification | 12 bolt rear cover, passenger car version has a different cover and is easily distinguishable  |
