1968 Chevy Nova Project Car - 12 Bolts To Glory
Building A Bulletproof Moser 12-Bolt For The Ultimate Multiuse Street Car.
From the December, 2010 issue of Popular Hot Rodding
By Cole Quinnell
Photography by Cole Quinell
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.
The new rear axle for our...
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.
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 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.
The axle tubing is seamless...
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.
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.
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
|Moser 12-bolt housing (base pricing)
|Moser 3.08:1 gears
|Moser setup kit
|Large Ford axle housing ends
|Multileaf spring pads
|Wavetrac 35-spline 3-series differential
|Moser Performance cover
|Semigloss black powdercoat
|Moser 1350 steel pinion yoke
Catch 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!
We're using a brand-new design...
We're using a brand-new design differential (see "Catch the Wavetrac") in our 12-bolt, but most of the assembly process is the same. You pick up some cool tips when you're in a pro facility like Moser that can crank out 35 complete axle assemblies in a day. Jim Ninde led us through his assembly process, including using a hot plate (rear of photo) to heat the ring gear and bearings to make slipping them on much easier.
From an installation standpoint,...
From an installation standpoint, the only thing unique with the Wavetrac differential is the first shim that sits next to the carrier in the housing. Because Wavetracs are only available in 35-spline, this shim has a larger inside diameter than usual. This is an extremely strong design that lets you use 35-spline axle shafts in your 12-bolt for maximum strength.
We opted for a 3.08:1 gear...
We opted for a 3.08:1 gear ratio and used Moser's ring-and-pinion gear set. We plan on using a three-speed Turbo 400 (no overdrive), so these cogs will let us maintain reasonable fuel efficiency on the highway.
With the pinion bearing installed...
With the pinion bearing installed but not the seal, Ninde checks the preload with an inch-pound torque wrench. With a 12-bolt, he likes to see 20 in-lb. Once he has the preload, pinion depth, and backlash he wants, the pinion is reinstalled with the seal in place.
With the ring gear nice and...
With the ring gear nice and hot from the warming plate, Ninde applies a dab of blue thread lock to each bolthole. He then slips the ring gear in place on the differential and torques the bolts. Moser offers a setup kit for most axles that includes ring-gear bolts, carrier and pinion bearings, seals, and shims.
With the carrier and pinion...
With the carrier and pinion installed in the housing, Ninde checks two things. The first is the ring gear backlash (shown). The second is the contact pattern on the ring-gear teeth. Adjustments are made by changing the shims, and one affects the other. Frankly, that's why we leave gear setup to the pros.
Moser Engineering has long...
Moser Engineering has long been known for its high-quality racing axleshafts, and that's still a core part of the company's business today. The axleshafts start off as forgings made in Portland, Indiana, from Moser-designed tooling. From there, all of the machining and processes are done on site. That gives Moser complete control and allows them to do custom work with a quick turnaround time. The street axles, which we used for this project, are made from a custom alloy, and are induction heat-treated to optimize torsional strength. Whatever you're building, they can make axleshafts that will deliver the strength and durability you'll need.
With all the increases in...
With all the increases in rear axle strength we're making, we decided to remove another fuse from the driveline. Instead of sticking with the stock 1310 U-joint at the axle, we had Moser install a pinion yoke that accepts a 1350 joint. Their steel yokes are much stronger than stock, and a 1350 joint has larger caps, larger trunions, and more needle bearings than a 1310. The downside is that we'll need to have a new driveshaft built to accept the larger U-joint.
The 30-spline 12-bolt axle...
The 30-spline 12-bolt axle splines (left) look puny in comparison to 35-spline axles. Moser custom alloy axles are induction heat treated and completely magnufluxed. They are engineered to take the abuse of racing and street use.
When you're building a new...
When you're building a new axle from scratch, it's easy to make good choices for strength. Originally, 12-bolts used C-clips to retain the axleshafts. This can be problematic in a performance application, and the preferred method is to use retainer plates at the end of the axle tube. We chose to use the large Ford housing ends that are made to accept axle-retainer plates and a variety of aftermarket brake packages.
We used a Moser Performance...
We used a Moser Performance cover for two reasons. First, for the functional justifications. The cover provides preload on the main caps and has drain and fill plugs making oil changes much easier. From a fashion standpoint, it looks really cool, and we wanted something to signify that this was not your standard 12-bolt rear axle.
The only thing left to add...
The only thing left to add to our new rearend is a set of brakes. For this project, we'll be using CPP's disc brakes to put on a modest but very functional pair of 10-inch rotors. The rear disc brakes are part of a total conversion kit that CPP offers for '62-74 Novas, which includes a power master cylinder, proportioning valve, front and rear rotors and calipers, brackets, bearings, and everything else needed for an easy swap.
The covers are made from 356-T6...
The covers are made from 356-T6 aluminum. The thick, machined gasket surface makes oil leaks extremely unlikely. The inside of the cover is designed to route oil slung off the ring gear to critical locations. The main-cap preloads minimize deflection as the ring-and-pinion try to force the carrier rearward under hard acceleration.