When we installed a 523hp Dart small-block in our 1968 Chevy Nova project car, we pulled the pin on the grenade that was the original rear axle. While it was fun doing peg leg burnouts on the ancient tires our Nova came with, we've since stepped up to a pair of 255/40R17 Nitto NT01s on the back. Horsepower and traction equal broken parts in between. So before we scattered the old 10-bolt axle, we decided to do the right thing and build a rear axle that will take the abuse.
Our Nova project car will see some autocrossing and road racing as well as drag racing, but the reality is that most of its miles will be accumulated on the street. We wanted a rear axle that was easy to install and wouldn't require any attention beyond fresh oil once in a while. The Moser 12-bolt promised this while also giving us the freedom to throw just about any level of performance goodies inside.
The new rear axle for our '68 Nova project car started out like all Moser 12-bolts: with brand-new parts made in the United States. The company has centersections cast from a higher-strength steel than the original, and there's no worry about cracks or fatigue from using a factory casting that's 40 years old.
The key advantage of an entirely new housing is just that: it's entirely new. There's no mystery about what it has been through and whether it is straight or has other issues. It's also extremely hard to find a decent used 12-bolt these days, and the ones you can find cost a pretty penny. You're never sure of the condition of the used parts inside, and you often end up replacing the differential, ring-and-pinion, and axle shafts. We'll let the numbers-matching guys fight it out over the swap meet 12-bolts. Another advantage is that you can set up a new rearend however you want. Moser has an axle configurator that lets you pick the differential, axle spline count, pinion yoke, gear ratio, and other factors. It shows the prices of each option and the total for the axle you specify.
For our Nova project car, we had already installed new 17-inch wheels from Vintage Wheel Works, so we were interested in an axle with the same flange-to-flange dimension. If you don't have your wheels yet, you can consider having a slightly narrowed rearend made to let you use wheels with more common backspacing or offset. We also wanted to try a brand-new differential: the Wavetrac. This is a torque-biased gear differential with several unique characteristics. See "Catch the Wavetrac" for more information.
The axle tubing is seamless steel with a 3-inch outside diameter and 1/4-inch wall thickness. The cast centersection is heated in a proprietary machining, and the axle tubes are pressed in for an interference fit similar to the factory, however, Moser welds the tubes to the housing all the way around the circumference of the axle tubes. From the factory, a plug weld is used on each side and that's it.
Moser installs new spring pads on the axle housing, so we planned to take the opportunity to upgrade from monoleafs to multi-leafs. (Look for that part of the upgrade when we head to Classic Performance Products.) This will decrease wheel hop a bit, and will make it easier to completely sort out traction. Another upgrade we opted for was to use a larger 1350 U-joint on the differential. This will require us to have our driveshaft modified to accept the larger joint, but the strength advantage will be worth it. We still have a little bit of work to do to swing the new axle under the Nova, but we can't wait to wear down our rear Nitto tires!
WHERE THE MONEY WENT Item: PN: Price: Moser 12-bolt housing (base pricing) N/A $1,804 Moser 3.08:1 gears 12B308 (included) Moser setup kit R12B (included) Large Ford axle housing ends 7750 (included) Assembly N/A (included) Multileaf spring pads (Included) Wavetrac 35-spline 3-series differential 5W1235-3 $887.50 upgrade Moser Performance cover 7110 $135 upgrade Semigloss black powdercoat $250 upgrade Moser 1350 steel pinion yoke PY100 $40 upgrade TOTAL: $3,116.50Catch The Wavetrac
The Wavetrac is brand-new differential made in the United States by Autotech Driveline. It's a gear differential that provides torque biasing, yet it has a couple of advantages over other torque-biasing differentials. When one drive tire has zero or nearly zero traction, most torque-biased differentials have a difficult time sending significant torque to the other tire. This is also true when transitioning from accel to decel. The Wavetrac uses wave-cut mating surfaces (shown in photo) on the side gears to provide torque to both tires in these situations. As the side gears move at different speeds, the wave surfaces climb each other. This pushes the side gears apart, creating internal load. The result is torque biasing in all drive situations and a smooth transition of power during the change from accel to decel. Basically, it's the perfect autocross and road race differential that should also provide extremely good traction on the dragstrip without any driveability issues on the street. The Wavetrac has a few other unique features, one of which is a transferable, limited lifetime warranty that even covers racing. You don't see that on many high-performance components!
