Moser's Killer 12-Bolt The last factory passenger car 12-bolt probably rolled off the assembly line under a Chevelle or Monte Carlo nearly 40 years ago. While cars and hemlines have changed many times, the GM 12-bolt is still considered the preeminent performance rear axle assembly for GM muscle cars. Moser realized this demand and began building replacement 12-bolt housings several years ago, which means you no longer have to search under rocks and in strangers' garages for these highly prized housings. This move to the Moser housing also eliminated the clumsy and dangerous C-clip rear axle retention technique. All current Moser 12-bolts now come with custom rear housing ends that use the larger Ford axle bearing and four-bolt retention flanges that retain the stock GM bolt pattern, so you can use the stock rear drum brakes if you like. But the biggest 12-bolt news is Moser's move to combine forces with AutoTech, a company that has created the Wavetrac-the newest and strongest limited slip for the GM housing. This limited-slip design uses new technology to apply torque to the opposite wheel even when one wheel is off the ground. That may not apply much in drag racing, but for street use and off-road enthusiasts, it is a big deal. What is news for drag racers is that the Wavetrac was designed for torque abuse with a 35-spline axle design, which is a dramatic strength improvement over factory 30- or 31-spline applications. Check out all the details on this new Moser 12-bolt. A. All Moser 12-bolts come with a large Ford bearing housing end that not only radically improves bearing size over the stock 12-bolt but also offers bolt-on axle retention that replaces the factory C-clip plan. These larger ends retain the stock 10- and 12-bolt backing plate pattern, which allows the use of either factory drum or aftermarket disc brake conversions. B. This particular Moser 12-bolt is configured for an early '64 to '67 A-body such as a Chevelle, an El Camino, a Buick Skylark, an Olds F-85, or a Pontiac Tempest. In the background is the original 8.2-inch-ring-gear 10-bolt that came in lower performance versions of these cars. The later '68 to '72 A-body 10- and 12-bolts will interchange, but the overall axle flange is wider by 1 inch. C. The aluminum rear cover/girdle employs a thick cast-aluminum cover that uses two studs adjusted down onto both main caps to lightly preload the main caps to help prevent bearing deflection under high loads. While two studs are included, the driver-side cap is the one that requires help, since that is the side where main cap load is the greatest. D. Moser 12-bolts all come with 3-inch housing tubes formed using much stronger 1/4-inch wall tubing and are fully welded into the center housing. GM 12-bolts used thinner tubing and were only rosette-welded into the housing at two places. A big advantage to a Moser 12-bolt is that large (3.150-inch-od) ball bearings replace the tiny stock 12-bolt axle roller bearings. We've learned to always use ball bearings on the rear axle to eliminate side-load difficulties with taper roller bearings (background). A big advantage to a Moser 12-bolt is that large (3.150-inch-od) ball bearings replace the With the Moser rear cover removed, the 3:73:1 gears and Wavetrac limited slip are easy to spot. The three-series Wavetrac is fitted with 931- alloy side gears machined for much stronger 35-spline axles. Typical stock GM 12-bolts came with thinner, 30-spline axles. The Wavetrac case is also much more robust and made of billet steel. The Wavetrac does require special extra-cost carrier bearings. With the Moser rear cover removed, the 3:73:1 gears and Wavetrac limited slip are easy to The Wavetrac limited slip uses much different converging/diverging elliptical plates located outboard of the side (differential) gears that are splined to the axles. As one wave climbs the other, the force pushing them apart generates increased side gear force that increases the torque bias. One advantage to the Wavetrac is that the torque bias can be altered in the field to custom-tune the torque bias ratio. The Wavetrac limited slip uses much different converging/diverging elliptical plates locat PARTS LIST DESCRIPTION PN SOURCE PRICE Moser 12-bolt Muscle Pak (base) call Moser Engineering $2,970.00 Wavetrac limited slip, 3-series 5W1235-3 Moser Engineering 995.00 Wavetrac limited slip, 4-series 5W1235-4 Moser Engineering 995.00 Wavetrac limited slip, 9-inch 5W9F35 Moser Engineering 995.00 Big Ford housing end, 12-bolt, pair 7900 Moser Engineering 90.00 SOURCES Moser Engineering 102 Performance Drive Portland IN 47371 260-726-6689 www.moserengineering.com By Jeff Smith Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!