It doesn't get much tougher than the 2 1/2-ton Rockwell axle. Used by the U.S. military for decades, these massive top loaders have continued to gain popularity in the off-road market, mostly due to their relatively cheap price. They are especially appealing for guys looking to run 44-inch-plus tires where weight is not really a concern. Responding to the increasing fame of this axle, ARB has stepped onto the scene with an all-new Air Locker designed as a full carrier replacement for the 16-spline 2 1/2-ton Rockwell axle.
As the first selectable locker to hit the market for these robust axles, the unit is intended to improve both trail and street characteristics over traditional full-time lockers. And given the fact that Rockwells are not factory-equipped with selectable hubs, dropping in a selectable locker is an easy way to improve your rig's steering and reduce wear on parts.
With the exclusive on the 2 1/2-ton locker and eager to put it in, we enlisted the help of Randy's Off Road in Azusa, California, so that we could rip into the roughly 700-pound axle with someone with a bit of big diff experience. It didn't hurt that he has a forklift to move the backbreaking axle!
The good news about wrenching on a Rockwell axle is that they are simple and you don't need to have a special engineering degree to rip one apart. The bad news is everything is very heavy and we must insist that you use an engine hoist, winch, or some sort of mechanical lifting device so that you won't write us angry letters about herniated discs and crushed toes! Even with the 6.72 gear ratio and massive size, we think there is much that can be done with these axles, and the aftermarket just seems to be warming up. Be sure to stay tuned. We plan to dive into the 2 1/2-ton realm with a little (big) project of our own.
1. There are three types of...
1. There are three types of Rockwell axleshafts: Bendix, Rezepa, and Spicer (shown). Our sources indicated that the Spicer (U-joint) style is the strongest, as it's the only one of the three made from heat-treated steel. The other two are comprised of cast metals. With the substantial 16-spline shaft measuring in an outside diameter of 1.62 inches, it's going to take a good bit of hammering before these shafts go pop.
2. The 2 1/2-ton third member...
2. The 2 1/2-ton third member is enormous and heavy. With the shafts removed we used a forklift to scoot around the heavy centersection and suggest the use of an engine hoist or some type of mechanical assistance since even with a couple guys, the third member can be too heavy and awkward to carry.
3. Sharing characteristics...
3. Sharing characteristics with the Ford 9-inch and 14-bolt axles, the differential is held in by two adjusters and four carrier bolts. It's a good idea at this point to mark each cap and check the backlash and contact pattern before removing the old unit.
4. Practically every bolt...
4. Practically every bolt inside the third member is safety-wired to keep any of the bolts from working loose. When reassembling the unit, it's a good idea to use new wire, which can be picked up at most hardware and automotive supply stores.
5. Generally equipped with...
5. Generally equipped with an open differential, our front axle was outfitted with a spool that dropped inside the original carrier. After unbolting the eight bull-gear bolts, we discarded everything but the 33-teeth gear and original hardware since the ARB is a full carrier replacement.
6. The new ARB Air Locker...
6. The new ARB Air Locker is a two-piece carrier fitted with a pneumatic ring sandwiched between the carrier bearing and differential. It is a relatively easy unit to assemble-you simply pull the two halves of the carrier apart, and bolt the bull gear in between. Being the first selectable locker available for the 2 1/2-ton top loader, steering no longer has to be an epic battle on the trail. With a flick of a switch you go from completely open to 100-percent locked.
7. Following the precise drilling...
7. Following the precise drilling instructions from ARB, you will need to drill a hole through the outside corner of the housing for the bulkhead fitting to thread into and the air line to feed through. In addition to drilling we found that the new carrier rubbed the housing ever so slightly. Erring on the side of caution, we opted to grind out a small section for it to clear.
8. As with any differential...
8. As with any differential swap, a new set of carrier bearings will be needed and can be picked up at most bearing, car part, or heavy-equipment service locations. With the new bearings pressed on and the differential set in place, torque down the bearing caps to 175 lb-ft and the adjusters to 25 lb-ft, making sure to set the adjusters for the proper backlash...
Then once the locker is secured...
Then once the locker is secured and the gear pattern checked, carefully feed the air line out of the housing. Securing the hard line from the locker is a bulkhead fitting that drops in from the outside of the third member. An air source will be needed to feed the locker and can be purchased separately from ARB.
Rockwell Third Member Basics
The 2 1/2-ton third members utilize a gear-reduction configuration that rotates power through a 2.44:1 ratio upper ring-and-pinion down to the 12-tooth intermediate gear and massive 33-tooth bull gear (2.75:1 ratio). This series creates an end ratio of 6.72. Weighing more than most complete 1/2-ton axles, the centersection raises roughly 9 1/2 inches above the axletube and has the ability to be turned 180 degrees, giving you the option of running either a driver- or passenger-side drop configuration.
Six-Lug
Our test truck had modified the Rockwell axles with a high-clearance differential skid and an off-road-only pinion-brake setup. With the 2 1/2-ton axles still sporting the factory hubs, shafts, and six-lug bolt pattern, we plan on thoroughly testing the Air Locker over the next few months. We'll be taking driver impressions as the 49-inch Iroks are sure to put the components to the test. For more about how the ARB Air Locker performed, cruise over to our website at www.4wheeloffroad.com.