Chevy Chevelle Rear Axle Swap - The Great Rear Axle Comparo

We started with three different... 

   

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We started with three different rearends, all with the same gear ratio. Our test would determine which one puts the most power to the ground.

We've all heard that the Ford 9-inch is the strongest rearend you can buy. According to the Ford guys at least, it's also the best overall decision for strength and durability. If pressed, they'll also accept that the 9-inch might eat a little more horsepower than the other-style rearends. Numbers are also tossed about like resolutions on New Year's Eve, but no one seems to know exactly. We've also heard that the Dana 60 is a killer piece but that it's monster heavy and overkill for anything short of a blown Hemi on steroids. What you also notice is that opinions on strength and efficiency tend to follow party lines. In other words, the Ford guys will vote for the 9-inch, the Chrysler guys will wave the Dana 60 flag, while the GM guys all line up behind the 12-bolt. No surprises there.

We decided to cut through the brand-loyalty blindfold to take a clinical look at the 12-bolt, the Ford 9-inch, and the Dana 60 rear axles. We obtained a 3.50:1-gear version of each of these three rear axle assemblies that would bolt into an early Chevelle to see which one eats the least power and also investigate how strong each assembly is, relative to the others. We enlisted the help of Currie Enterprises, Moser Engineering, and Strange Engineering to supply both parts and expertise with this evaluation. Then we chassis dyno-tested all three at Westech on a SuperFlow SF-790 using our small-block Chevelle to see which one could put the most power to the ground. We chose a Chevelle mainly because it was accessible and because the 383ci small-block made decent power at the crank. The results were certainly worth the effort.

GM 12-Bolt
We started with a stock, early Chevelle 12-bolt housing that had been modified by Sutton Engineering with Moser large Ford bearing housing ends that allow the use of either stock drum brakes or a bolt-on disc-brake package. Because the original 12-bolt housings are now more than four decades old and hoarded by collectors, Moser offers brand-new bolt-in housings along with axles for a reasonable price. The larger Ford bearings are much stronger and use a four-bolt axle retainer plate, like a Ford 9-inch. This eliminates the stock C-clips and uses an aftermarket Moser 30-spline axle. We could have opted for a 33-spline axle, but we felt we didn't need that kind of strength for this test.

In addition to the 3.55 gearset,...        read full caption In addition to the 3.55 gearset, we also chose a Detroit TrueTrac limited slip along with a complete Moser installation kit.

Our stock 12-bolt housing...        read full caption Our stock 12-bolt housing was modified with Moser small Chevy car housing ends that use the big Ford 9-inch axle bearings. We had to enlarge the center hole in the stock Chevy drum backing plates to a 3.150-inch dimension to fit the Moser aftermarket axles and larger Ford axle bearing through the backing plate. Moser also supplied new plates that fit over the four bolts to retain the axle.

We also utilized a Moser performance...        read full caption We also utilized a Moser performance aluminum cover that improves gear life by placing a slight preload on the differential main bearing caps with the integrated Allen bolts. The cover also comes with a new gasket and necessary hardware.

We also spec'd a set of Moser 3.55:1 street gears, a Detroit TrueTrac limited slip, and a 1310-series U-joint pinion yoke. To add a little more strength, we also included a Moser aluminum rear cover that uses Allen preload bolts to support the main caps under load. Tim Moore installed the ring-and-pinion for us. While we chose Moser as our source for 12-bolt parts, Currie and Strange also offer complete 12-bolt rearend assemblies as well as individual components.