Even at 30 splines, the 12-bolt's greatest weakness is the lame direct-acting bearing, c-clip- axle arrangement. The only thing this stuff is good for is keeping production cost low when you're GM and you've got to build millions of axles for cheap. If you're a die-hard, Moser does offer high-grade 30- and 33-spline c-clip axle shafts that are NHRA-legal. | 
We specified Ford "big bearing" tube ends and sealed axle bearings. Available in a few flavors, our tube ends are designed to accept Chevy drum brake backing plates so Mike could reuse his stock 10-inch Nova drums. While we were at it, we also upgraded to 33-spline axle shafts, a no-cost upgrade if a spool is specified (limited-slip customers pay a small added charge for 33-spline compatibility). Be sure to tell Moser what brakes you plan on using so you get the correct axle flange offset. | 
The stock Chevy brake backing plate has a 2.7-inch center hole. To accommodate the Ford axle bearings and retainer it must be enlarged to 3.150 inches with a die grinder. This hassle can be skipped by ordering Ford drum brakes (with the Chevy bolt pattern, of course), but Mike had just rebuilt his Nova's drums and couldn't bear to toss them. |
Mike runs Centerline rims, so he specified the optional 5/8-inch-long wheel studs for $80. The stock studs are puny 7/16 twigs. | 
Mike selected a 33-spline Moser spool (left) instead of a clutch-type Posi-Traction unit. The spool suits the hard-charging Nova's need for uniform power delivery to both slicks. Buyers have their choice of either type of differential for the same money, though 33-spline customers will pay a little more for a 33-spline limited-slip unit. | 
The optional cast-aluminum inspection cover ($135) features pre-load adjusters that bear gently against the carrier-bearing caps to prevent deflection and gear-mesh irregularity. The pre-load is set to 5 ft-lb. Dig the handy fill and drain plugs. Before ordering the special cover, make sure you have adequate gas tank clearance. |
Our thanks to Jim Cook and Performance Differential for providing disassembly and reassembly services. Jim's ready to help you with your rear axle parts and service needs. | | |
OE Fortification: False Economy?
If you're maybe thinking you can get it done cheaper the old-fashioned way, here's a ballpark cost analysis of what it takes to refurbish and fortify a stock GM 12-bolt rear axle. The total amount is within striking distance of the Moser base price. As for the shipping charges, contact Moser for specific pricing, but rest assured you may spend more running all over town rounding up parts if you attempt this in do-it-yourself mode. Think it over, then make the call!
*Used 12-bolt case housing: $100 to $250 (when you can find one)
*Re-tube 12-bolt case to your width: $379
*Custom axle tube ends: $80
*Custom alloy axle shafts: $315
*Differential setup kit: $100
*Spool: $190
*Ring-and-pinion: $155
*1350-series pinion yoke: $130
*Upgraded wheel studs: $80
*Setup labor: $125
TOTAL = $1,645 to $1,795