GM 12 Bolt

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 these details.

 

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

 GM 12 Bolt axle identification