GM 12-bolt
This axle was manufactured in both 5- or 6-lug bolt patterns. If you trash the 12-bolt in your '73-to-early-'80 4x4 Chevy truck, you'll be happy to know that you can simply install your 6-lug axleshafts into a two-wheel-drive 12-bolt axle and return to the trail.
Application: Rear.
Type: Semi-floating.
Spline count: 30 (after '68.)
Factory ratios: 2.50:1 through 4.56:1.
Maximum recommended tire size for stock axle: 35-inch.
Strong point: Larger-diameter ring gear than 10-bolt (8.875-inch).
Weak point: The pinion bearings are small and fail often.
Junkyard jewel: Some '76-or-older Chevy ½-ton trucks had a good Eaton coil-spring-type limited-slip.
Building secrets: Some ratios allow the use of a 12-bolt automobile gearset, which, interestingly, uses a larger-diameter pinion shaft.
Aftermarket alternatives: Currie Enterprises, Custom Differentials, DTS Custom Service.