The Chrysler 8 ¼ axle has been around many years, and is most recently fitted into the rear of Dodge Dakotas and Jeep Cherokees. While a fairly substantial diff, and a lot better than the 35C found in earlier rigs, it is a small, C-clip design axle, which makes fitting traction diffs into it a bit difficult. We advocate axle upgrades all the time, but we can’t all afford a custom Dana 60. Many of us want to be able to upgrade what we already have, and that factory Trac-Lok just doesn’t cut it on the tough trails. You could simply get an Auburn limited slip, a Detroit Locker, or even a Powertrax unit, but the folks at ARB wouldn’t supply an Air locker—that is—until now. One of the reasons for this is that the smaller a differential, the more critical the design needs to be for maximum strength and performance. That’s why ARB has recently released its second-generation Air Locker, which makes a good thing even better.
With a bulletproof two-piece carrier and timed spider gears, the new unit is also easier to install with fewer problems with air leakage. This new design eliminates the long through-bolts holding the three-piece unit together, and moves the air inlet from the right-side carrier bearing to the bearing assembly near the ring gear flange. This greatly increases the rigidity and strength of the case itself, while eliminating the need to modify the bearing caps by notching or drilling. Most important, new timed gear technology ensures that all four spider gears are more positively engaged with the side gears so that torque loads are evenly distributed within the unit.
Since we needed bigger rubber for more clearance (and the accompanying lift), we opted for this new ARB as a one-finger wonder in the engagement department, and trundled off to Drivetrain Direct for an install. At the same time we popped in some 4.56 gears (the lowest available) so our new Cherokee can handle the bigger meats. With the new ARB seal design on the air inlet, installation is much easier and quicker, which saves time and money in the labor department. Check out how we upgraded what we have, rather than dropping tons of cash on custom axles.
An oval cover with 10 bolt holes and a raised edge on the cover means you probably have an 8 1/4 axle. These units were used until '96 with 27-spline axles. The '97-and-later styles feature a beefier 29-spline style. Axles can be swapped if you have the smaller axles, since the ARB only fits the 29-spline axles. While this rearend isn't equivalent to a Dana 60, it's about as strong as a Ford 8.8 or a Chevy 10-bolt. | 
The 8 1/4 Chrysler rear is a C-clip design, which means the axleshafts are held in the housing by C-clips on the end of the axleshafts. After popping the cover and draining the oil, the crosshaft retaining pin and crosshaft are removed from the stock carrier. With the axles pushed all the way in, the C-clips can be removed with a magnet, and the axles can be removed. The tires and wheels don't have to come off the axles, but it's easier since you need to pull the axles all the way out when adjusting the gears and bearings. | 
Like all ARB diffs, a hole needs to be drilled in the housing for an air fitting to be installed. Remove the carrier bearing bolts, caps, and adjusters, then remove the stock carrier. If you're changing ratios, remove the driveshaft and pinion yoke, then drive the pinion out, followed by the pinion races. Finally, drill and tap the air hole with a 1/4-inch NPT tap in the correct location, then clean the housing up within an inch of its life. |
If you're keeping the same gears, cover the pinion with a rag when drilling the air hole. Since we went to deeper cogs, we pressed new bearings on the new pinion with the stock shims, hoping the pinion depth would be right. New pinion races were tapped into the housing, and the pinion was installed. If the depth is right on when checked with the pinion depth gauge, install the crush collar, yoke, and seal to adjust bearing preload. This is a good reason to have a shop set up the gears if you don't have the tools or experience in this department. | 
Another problem with low gears is that the ring gear tooth near the crosshaft needs to be ground down a bit for clearance. After a mock up, we knew where to grind and buzzed the offending piece off. This is a common practice and shouldn't affect the gears so long as it is done correctly and you use quality gears. Clean the gear thoroughly in hot soap and water after the modification is over. | 
Assemble the new cleaned ring gear on the ARB carrier, and use Loctite on the ring gear bolts. Since the left side of the ARB houses the new seal/bearing assembly, only the right side (which is where the seal and air line is on older models) needs to have a new carrier bearing pressed back on. |
Here's where the new second-generation design helps the installer. The copper air line now enters the carrier on the left side near the ring gear. Previous designs have a separate seal housing with two U-rings for sealing and could be damaged on installation. The new design has the seal housing and O-rings factory installed. On the 8 1/4 unit, the carrier is set in place, then the carrier bearing ring adjusters are installed, and then the carrier caps. The bolts are only tightened down finger tight so the backlash on the gearset and the bearing preload can be adjusted. | 
What used to be the hard part is now quite simple--aligning the copper air line into the hole in the housing. The new style ARB doesn't require notching or cutting of the bearing caps, so no misalignment results. Bend the line into the hole and attach the special fittings, then run the air lines up and away to where you've located the compressor and run your electrical wires for the switches. | 
A special tool is inserted down the axletube to adjust gear backlash and bearing preload. Tighten each ring adjuster for a tad of preload on the bearings, then use them to move the ring gear closer or farther away from the pinion gear to obtain the correct backlash, usually 0.004-0.007 inch as measured with the dial indicator. Paint the teeth with marking compound and verify that the pattern is acceptable for smooth and quiet operation. Tighten up the side adjusters for proper bearing preload, and insert the lock plates to finish it off. If you aren't familiar with this process, you might want a professional to dial this stuff in. |
Slide the axles back into the housing and install the C-clips. The crosshaft can now be slid past the ground-off portion of the ring gear to retain the C-clips. An improved threaded crosshaft retainer is now used instead of the old style that required a special tool to remove it. Whew! Not too much work, eh? Slobber some goo on the cover gasket and slam the lid home, then fill the pumpkin with quality 90-weight. Now a one-touch wonder is ready to hit the rocks. | | |