One of the most enjoyable aspects of the four-wheeling hobby is the challenge of exploring new places. The road trip helps you build confidence in your rig, and having a great weekend off-road simply reaffirms why this hobby is so great. As much as we like hitting the road for a faraway ’wheeling destination, we try to build our rigs for the terrain that we wheel the most. Building for where you actually wheel, versus where you would like to wheel, is often tricky for ’wheeling enthusiasts, and we completely understand why.
Our ’99 Jeep Cherokee is a great case study in building a rig to satisfy both our ’wheeling needs and wants. When we purchased the Jeep from the previous owner, we knew the stock axles were not part of the deal. So, we had to find replacements. Grabbing a high-pinion Dana 30 front and 8.25 rear from our local pick-and-pull would have been extremely easy, but we knew the stock axle set wouldn’t be up to par for the adventures and tire size we had in store.
With the types of trails around the Southeast (where the XJ is located), a 37-inch-tall tire is a great balance of size-to-terrain. Sure, there will be places 37s are overkill and other spots where it just isn’t enough. Ultimately, it’s a size that suits the 103-inch wheelbase well and allows us to keep the XJ low and versatile. The wide array of tire choices also makes a 37-inch tire an easy pick.
G2’s Core 44 rear axle is engineered as a direct replacement for the ’07-current Jeep Wrangler JK. We didn’t need all of the JK suspension brackets for our XJ project, so we asked that the axlehousings be shipped sans mounts.
Axle options are plentiful these days and can be as high- or low-buck as your budget will allow. In our experience with XJs in general, we’ve found they benefit greatly from the added stability of a wider axle. Typically, this means going with heavy 1-ton axles (which in our case would be overkill). We didn’t want the weight or ground-clearance penalty of the ’tons, so we started looking elsewhere.
A benefit when wrenching at a shop is that they typically have parts sitting on the shelf.
This led us to look at ’07-current Jeep Wrangler JK axles. Even if you are not a fan of the JK platform, the aftermarket support for the late-model Jeep is undeniable. Initially, the 65-inch axle width and major parts support drew us in to the JK axles. Having owned a few JKs, we were also aware of the pitfalls of the stock JK axles. After doing the math, we calculated that by the time we built a junkyard set (which we found incredibly difficult to find an unbent set), we would be close to the price of a brand-new aftermarket housing.
In the end, we opted for a set of G2 Axle & Gear Core 44 axles. The JK-specific aftermarket housings are designed as a bolt-in upgrade for the current Wrangler platform, but clearly, we had other plans. Once the Unitbody inevitably crumples away, we can transfer these axles to another project, so the investment is sound. In this installment, we are working on fitting the rear axle in place. Next month, we’ll show you what it took to secure the front axle under the XJ, as our Disposable Hero project starts to really take shape.
Step By Step
Each Core 44 differential is designed to accept an array of aftermarket differential lockers. For those with Rubicon JKs looking to upgrade, G2 has machined the housings to accept the stock Tru-Lok selectable lockers, so you can transfer over your factory Rubi lockers. To take care of the common bending issue associated with the rear axletubes, G2 used 3-inch, 0.250-wall DOM tubing.
Once you’ve experienced the benefits of a selectable locker, it’s hard to go back to an automatic locker. This is especially true in the rear of a Jeep. We opted for a tried-and-true ARB Air Locker for our Core 44 axle. The two-piece case design uses forged gears and should have no trouble handling the power of the 4.0L engine or grip of our 37s.
An extremely unique and installer-friendly feature of the G2 Core differential is the ability to set the backlash and carrier bearing preload through the G-lock adjustable spanner nut design. Our 5.13:1 ring-and-pinion, along with the master install kit, came from G2 Axle & Gear as well.
ARB’s RD157 Air Locker only accepts 35-spline axleshafts. The 35-spline, 1.5-inch G2 chromoly rear axleshafts are closer to what you would find on a 1-ton rear axle. The ’shafts came with Set 10 wheel bearings, studs, seals, and bearing retainers. The ’shafts are also fit with the stock JK 5-on-5 wheel bolt pattern, as well as 5-on-5.5.
One of the more challenging aspects about the XJ to JK axle conversion was digging up stock JK parts. G2’s Core 44 axles are designed to re-use your stock JK brake parts and backing plates, neither of which we had. Luckily for us, our host build shop Low Range 4x4 had completed a 1-ton JK axle conversion recently and still had the axles sitting in storage. This allowed us to grab the few components we needed.
As we mentioned, we were starting from scratch in the brake department. For rotors and brake pads, we ordered a replacement set from the Jeep mega-parts house Omix-ADA. We purchased the calipers from our local parts house.
A benefit when wrenching at a shop is that they typically have parts sitting on the shelf. We grabbed these oxidized, but unused, leaf-spring mounts for mockup and quickly found that they would work fine for our 21⁄2-inch wide Rubicon Express spring pack.
Our shock tabs were another item that we had to graft onto the bare housing. Low Range happened to have these on the shelves, which fit perfectly on our 3-inch axletubes. The stud-style tabs allowed us to keep the shocks in a similar position as they were from the factory.
After taking multiple measurements to ensure the axle was square under the Jeep, we placed the axle on jack stands and used a floor jack to set the pinion angle. Once we were happy with the degree, Low Range owner Kelly Carter welded the perches in place.
The Rubicon Express spring pack is a bit worn, but we are going to keep them for now. After we disconnected the old shocks, we quickly realized that they were both bent and blown. We replaced the old absorbers with a set of Rubicon Express monotube series shocks, which are valved for the company’s 4.5-inch XJ suspension system.
For both axles, you have the option of 1310 or 1350 yokes. We opted for the 1310 as it offers plenty of strength for our XJ. For now, the XJ’s rear driveline will work to move the Jeep in and out of the shop, but once we hang the front axle, we will upgrade the worn axle propellers.
If you are upgrading your JK Rubicon 44 differentials with an ARB Air Locker, we suggest using the PPM-4033 kit from Synergy Manufacturing. The Synergy air line guide bolts in place of where the Tru-Lok actuator originally attached. This prevents you from needing to drill a hole in the housing to run the air line.
G2 fits its Core 44 with heat-treated aluminum diff covers, which have cooling ribs and room for more fluid over a stock Dana 44 cover. Like the axlehousing, the cover is made in the USA as well. That’s one trend we would like to see more of.
After dousing the rear axle with a rattle-can finish, we ran the hard brake lines to the calipers. We still need to grab the correct banjo bolts, but for the most part, the rear axle is ready to roll.
A major attraction for us to the JK axle is the fact that it’s 65 inches wide. That’s roughly 41⁄2 inches wider than the XJ’s original axles. While it might not seem like much, it’s a major improvement in stability.
Here’s a sneak peak at what we are looking at for a ride height. The Maxxis Trepador M8060 37x12.50R17 tires are mounted on 17x9 ATX Chamber Pro II beadlock wheels. The 4-inch backspacing doesn’t quite push the tires completely out from under the XJ. So, we have a bit more trimming and bumpstop engineering to do to maintain the 4.5-inch lift height.