There are so many Jeep JK Wranglers on the roads and trail today you can’t swing a dead cat over your head without hitting one. And that’s a good thing. Not the swinging a dead cat thing, but that there are so many JKs out there. Now more than ever, the Jeep brand is alive and kicking. However, mixed in with all those JKs, we’re starting to see more and more TJs, YJs, and XJs being freshened up for the trail. These 10 to 20-year-old rigs are hot because they can be found for reasonable money, are good foundations to build upon, and they’re not overly boogered-up with electronics.
So, if you have been and continue to see a lot more articles here about those three models of Jeeps, don’t be surprised. That, like a drum roll, leads us into this article about slinging new and much beefier axles underneath an XJ. And we’re not talking about just any axles. We spent a day (or two) working with the folks at Currie Enterprises to build front and rear RockJock 44s for a 1992 Jeep XJ Cherokee. Why RockJock 44s? Well, because they are custom-built logs made to order, and can be created to easily fit underneath a JK, TJ, YJ, CJ, or XJ. As a matter of fact, they can be built in such a way that with custom mounts you create, they could go under almost anything, but that’s another story.
The Currie RockJocks come in Dana 70, 60, or 44 spec, and for our purpose, we went with the 44s. The RockJock 44 center housing was designed by Currie, is cast in ductile iron, offers more ground clearance than a traditional Dana 44, is thicker in critical areas, offers improved oiling, and is available in either low- or high-pinion designs. High-pinion units are especially desirable for frontend applications with short driveshaft lengths. The tubes are 3x.375-inch-wall steel tubes, with Ford Torino–style ends (our unit for the XJ was fit with the 11-inch Ford Explorer disc brake kit) on the rear axle and knuckles to suit the customer’s needs (our front axle were built with TJ/XJ knuckles) on the front axle. The axleshafts (front and rear) are induction heat-treated 1541 forged steel alloy ’shafts and come in 30, 31, 33, or 35 spline applications. Sounds like a winner. Follow along as we show you how they were built and all the work that goes into creating the Currie RockJock 44 axles.
This is the heart of the Currie RockJock axle (the front Dana 44 high-pinion non-Rubicon for our Jeep XJ seen here). It’s a heavy-duty ductile iron casting designed by Currie to have thicker walls all the way around than the standard Dana 44. It also has a special reservoir above the pinion shaft that feeds oil to the shaft and its bearings. Front and rear centersections are heated in a high-temperature oven while the axletubes are being cut to allow the expansion of the centersections axletube sockets. This allows for easier installation of the tubes, a job done while the centersection is still too hot to touch without thick gloves on.
Because all RockJock axles are custom-ordered, the axletubes are cut to length, and then both ends of the tubes are milled. The Currie RockJock 44 features 3-inch by 0.375-inch wall steel tubes. A small amount of material is removed from the outside of the inner tube-ends to create a perfectly smooth surface for a better seal with the centersection. The outer tube-ends are also milled and chamfered to make them ready for the bearing housing ends (rear axles) or knuckles (front axles).
Once the axletubes have been inserted into the centersections (front axle shown here), they are set into a jig and plug welded together through holes in the centersections’ tube ports. Steel rings are temporarily placed where the carrier bearings will be, and then bolted into place underneath the bearing caps. A steel rod is run through the entire axle assembly (and those steel rings) to keep everything straight during the final welding process. The axle knuckles (which are bolted up to jigs made from steering knuckles) are slid over the rod and bolted into place on the axle-tube ends (a level is used to maintain correct clocking in relation to the centersection), and then welded to the axle-tube ends.
A special jig is used next to locate and then tack weld all the necessary brackets (shock mounts, spring perches, link arm mounts) to the axle assembly (front RockJock 44 for our XJ Cherokee shown here). Once all the brackets are tacked into place, one end of the rod goes onto rollers, and the other end goes into a rotating chuck controlled by a foot pedal. The entire axle assembly is slowly spun during the final welding process.
As with the front axle, the rear axle centersection and tubes are plug-welded together, steel rings temporarily bolted into place underneath the bearing caps, temporary axle ends for the rod to go through (these temporary axle ends are also used to vise-grip the permanent axle ends to the axle-tube ends prior to welding) are placed at the ends of the axles, and a steel rod inserted through the entire axle assembly.
The axle ends are properly clocked and clamped into place, and then tacked-on prior to final welding. Careful measurements are made and levels used to also precisely locate and properly clock the spring perches in relation to the centersection (note angle indicator on pinion surface of the rear axle’s centersection in photo) for correct pinion angle before they are tack-welded into place.
The rear shock mounts were also properly clocked on the axletube prior to being tack-welded into place. The rear shock mounts for the Cherokee XJ are on opposite sides of the axle (one in front, the other in the rear) and five degrees out of clock registration in relation to the centersection.
The Currie RockJock 44 front and rear axles came with complete master bearing set up kits (the one for the rear shown) that included bearings/races, shims, hardware, and seals.
We opted for Eaton ELocker electronic locking differentials in the front and rear Currie RockJock 44s that were headed for installation under our ’92 Jeep XJ Cherokee. These are top-shelf units that lock instantaneously with the flip of a switch. We like them because there’s no waiting for an air compressor and no need for an air tank.
Because we decided to go with 4.56:1 ratio ring-and-pinion sets from Motive Gear for our Currie RockJock 44s, we had to be sure to order the high-ratio ELockers from Eaton. Eaton builds two versions of the ELocker for Dana 44 spec axles, and the split is at 4.56-4.10. A numerically lower (4.10:1, 3.73:1, etc.) gear ratio requires one version called the “low-ratio;” 4.56:1, and a higher numerical gear ratio requires another version called the “high ratio.” It’s all a matter of different ring-gear mounting flanges on the two different Eaton ELocker “versions.” Be sure you order the right one. We also ordered special “JK” gears, which have a thicker ring gear, because the Currie RockJock 44s are designed to take the heftier gear sets.
The use of Lock-Tite (Red) is a must-do when it comes to installation of a ring gear to any differential carrier. Quickly after the Lock-Tite was applied, we properly torqued (according to manufacturer’s specs) the Motive Gear rings to the Eaton ELockers using a rolling-star sequence pattern.
Starting with a pilot bit, we then went to a 15/32-inch drill bit to create the passage for the wire (and grommet-seal) that will bring an electric signal to the Eaton ELockers soon to inhabit each of the Currie RockJock 44 axles.
Just when you think everything is perfect. Well, to be honest, this is not the first time we had to shave off (carefully with an abrasive wheel on a die grinder) a bit of material from the ends of the bearing caps to make them clear a tang or wire on the lockers.
Bearings and seals were installed in the front and rear axles for the pinion shaft and the carrier. Bearings were also installed on the pinion shafts (using a press) and the Eaton ELockers. The pinion shafts and pinion yokes were installed (with shims and seals), and then we carefully slid the lockers into place inside the Currie RockJock 44 axles. A few good taps with a rubber hammer made sure they were properly seated in the axle-centersections. We took care to not damage the wires protruding from the lockers during this process.
We’ve never had setup on any axle be perfect the first time, so it was not a surprise that it took a few adjustments here and there with the shims on the pinions and the sides of the differential carriers to get it just right in the front and rear Currie RockJock 44s. The front axle took 0.024 inches on the pinion, 0.028 inches on the driver side and 0.025 inches on the passenger side of the carrier, and we ended up with 0.010-inches of backlash. The rear axle ended up with 0.008 inches of backlash, 0.040-inches of pinion shims, with 0.030-inches on the driver side and 0.027 inches on the passenger side of the carrier.
Because the gear teeth on the pinion can become nicked a bit during setup, once the right combinations of pinion and carrier shims had been established, all were disassembled so that the gear teeth on the pinion could be ever-so-slightly touched with an abrasive wheel to make sure they were cleaned up before final assembly and closure.
The electrical wires (and grommet-seals) for the Eaton ELockers were carefully installed through the 15/32-inch drilled hole in each axle. A pre-existing hole in each of the cast iron centersections was tapped and threaded so the brass NPT fittings for the breather tubes could be installed. Johnny Joints were also installed in the front Currie RockJock axle’s control-arm mounts at this time.
Once the differentials and pinions were all buttoned up again, gasket sealer (we used good ol’ RTV) was applied underneath and atop the gaskets for the axle center-section cover plates. Then the cover plates (we chose Currie’s heavy-duty, red-texture finished cast iron cover plates) were tightened down to the manufacturer’s prescribed torque settings.
The new Currie front axleshaft assemblies were installed in the front axles, and the Currie rear axleshafts were inserted into the rear axles (after the new brake backing plates and parking brake assemblies were installed on the rear axle end plates). These axleshafts are custom cut and splined, induction heat-treated, 1541 forged steel alloy and can be ordered in 30 (our choice to fit the ELockers), 31, 33, or 35-spline patterns. The front halfshafts were designed to accept 760X U-joints. The rear ’shafts feature 1/4-inch thick retainer plates, and are available in bolt patterns up to 6-on-5 1/2-inch and wheel studs up to 1/2 a 3 inches.
With the front Currie RockJock 44 done and ready for installation, we turned to the rear axle and installed the new Currie disc brake hats. The final step was to install the assembled rear disc brake calipers and then hook up the flexible brake hose to the caliper and thread the other end of the brake hose through the fitting brackets on the rear axle.
We’ll tackle the complete installation of the front and rear (rear shown here) Currie RockJock 44s, including the electrics, front brakes, shocks, and springs (and give you some tips and tricks we learn along the way) underneath our ’92 Jeep XJ Cherokee in the next issue of Jp. Stay tuned!