Our Doomsday Diesel project is a physical manifestation of the Boy Scout motto: Be prepared. While we know the end of the world isn’t coming in 2012, the media frenzy has given us motivation to be ready for the future.
| doomsday Diesel Part 4 gm 14 Bolt Axle
As diesel owners, we are all well positioned to thrive in an ever-changing world. The mere fact that we’ve invested in heavy-duty trucks that last twice as long, are biofuel compatible, and are designed for multiple roles ensures we’re ahead of the curve.
December 21, 2012
Our monthly buildup series focused on swapping a Cummins diesel into a ’91 ¾-ton GMC Suburban is intended to highlight the reliability and simplicity of the diesel hardware in our market. By bringing aftermarket and junkyard components together in an older vehicle, we plan to end up with a machine that’s so reliable, it could theoretically last forever.
To that end, we’ve chosen a drivetrain that’s not only bulletproof, but belly-button common. Doomsday Diesel’s ’95 5.9L Cummins (“Million-Mile Cummins Rebuild,” April ’12) will be mated to a TCI Auto 4L80E transmission and a BorgWarner transfer case with a PTO provision. To ensure our Cummins’ power gets to the ground, we chose the largest axle ever offered in a single-rear-wheel pickup: the AAM 1150.
The 14-Bolt Axle
For decades, GM built its rear axles in-house, so magazines like Diesel Power would give these rearends names like Corporate 10-bolt, Corporate 12-bolt, or Corporate 14-bolt—based solely on the number of bolts holding the rear differential cover on. When American Axle & Manufacturing (AAM) was formed in the ’90s by a group that purchased GM’s axle manufacturing facilities, its axles were branded with new AAM designations. The new naming structure was a combination of the manufacturer’s name (AAM) and the diameter of the axle’s ring gear gear.
| We bought this complete ’02 Silverado 2500HD 14-bolt AAM 1150 rear axle on Craigslist for $300.
The AAM 1150 axle we’re using features 3½-inch-diameter tubes, an 11½-inch-diameter ring gear, 1½-inch-diameter axleshafts, and full-floating wheel hubs. It’s a larger version of the 9½-inch (AAM 950) and 10½-inch (AAM 1050) 14-bolt axles GM has used in diesel pickups since the 6.2L days.
Duramax-powered pickups have used the AAM 1150 since its ’01 model, and Dodge has offered it (using most of the same parts) since its ’03 model. We like this axle because it’s simple, strong, and there are zillions of pickups on the road using it. That means parts availability will be good for decades to come.
Zombie-Proof Upgrades
For those of you who have this axle in your ’03 to ’10 Dodge or ’01 to ’10 GM pickup (the ’11-and-newer versions are slightly different), we’re going to show you how we replaced the factory Gov-Loc differential with a battlefield-proven Eaton Detroit Locker. We’ll also clue you in on a simple pinion upgrade, which allowed our truck to use a stronger driveshaft. We’re even going to publish all the factory torque specs for the GM version of this axle—since we hate it when instructions tell you to “torque it to the factory specifications.”
| When we pulled it apart, we found it had 3.73:1 gears—meaning this axle was originally from a Duramax truck. Our core axle also had the optional Eaton-built Gov-Loc locker. This diff is a perfect unit for 99 percent of us, but we wanted something more aggressive for Doomsday.
