For ’67-’72 Chevy pickup owners, there are a number of reasons not to get rid of that 12-bolt Chevy rearend under your 1/2-ton. For one, the darn thing fits. All the suspension components bolt right up, with the traction bar pickup point cast into the housing from the factory. And unless you’re going to add some serious tire under your truck or a wheel with a deep offset, the width is good to go as well. They’re also tough as nails, equally so to the much more touted Ford 9-inch, with a more efficient design thanks to a lower pinion position in relation to the ring gear centerline. This results in a 3½ percent horsepower increase through reduced friction and lower gear lubricant temperatures.
Here’s the stock outer axle roller bearing. Note that it lacks any ability to control side load or to retain the axle in the case of a broken internal C-clip.
But as great as the 12-bolt truck rear sounds, there are some drawbacks. For one, they retain the axle C-clip design carried over from the lighter weight passenger car rearends. Snap the axle-retaining C-clip and the entire axle assembly, wheel, tire, and all, can make an abrupt run to the hills. Not such a good scenario. The second problem with these rearends comes in the form of the outer roller bearings. These non-tapered bearings ride directly on the axle itself, which means that if your rearend is suffering from sloppy axle bearings, you’re most likely going to have to replace both the bearing and the axle as there is no bearing race to replace. That can become both costly and irritating if you drive your truck hard. The other problem with this style bearing is that by its very nature it suffers from side load difficulties. Without a way to keep the axle tight against the housing, bent axles, broken C-clips, worn-out bearings, and an overall sloppy nature is the result.
But there are some solutions to these problems that make retaining that factory 12-bolt a very real option to even the most demanding C10 enthusiasts. And when compared to the cost of building an equally strong, custom Ford 9-inch from scratch, the 12-bolt makes even more sense.
The “race” on the stock Chevy axle is actually just a machined face on the axle itself. Once worn, the axle needs to be replaced to remove any slop.
I pulled the 12-bolt rear out of my latest project, a ’68 Chevy longbed, while we were getting rolling on the suspension upgrades and took it down to the local go-to guys when it comes to rearends, Currie Enterprises. They pointed out the aforementioned shortcomings the 12-bolts suffer from and made their recommendations to create a bulletproof GM rear. When it was all said and done, the upgraded rearend bolted right back into place, strong as an ox and with a posi third member to replace the stock peg legger. We’ll start the suspension upgrades next month, but first let’s get this rearend rebuilt and ready to go! CCT
