Most of us don't think about modifying our Jeep's axles until after we're up the creek without a paddle and elbow deep in axle grease. The Dana 30 front axle and Dana 44 rear that came in our '04 1/2 Wrangler Unlimited would hold up just fine in stock applications running the original tires and wheels. However, these axles became marginal when we threw on our 5 1/2-inch lift kit and 37-inch tires, and actually put the thing into four-wheel drive. As tire size, vehicle weight, and off-road abuse increases, the life expectancy of your drivetrain decreases. The axles just weren't designed for the extra stress. It's not uncommon for overloaded and abused axles to spit out their guts like an Olson twin right on the trail. Of course, there are plenty of add-on parts to increase the internal strength of the factory axles; however, these often-expensive components can only do so much for overall axle strength. That's why we stepped up to axle assemblies that are designed so we really don't need to carry spares or worry about making trail repairs.
Dynatrac put together some of its Pro-Rock 60s for the Awesome Unlimited and stuffed them with its brand-new competition 40-spline shafts and lots of other new goodies. Most axle swaps can be a nightmare; however, Dynatrac has built plenty of Jeep axles and makes sure all of the bracketry is correctly located. Our Pro-Rocks came completely assembled, so all we had to do was bolt them up. Keep your eyes peeled for the next issue where we'll wrap up the project and give you a rundown of how it all works along with any changes we have planned for the Awesome Unlimited.
To run 40-spline axleshafts, you really only have two choices for your differential. You can go with a full spool or a Detroit Locker. We went with Detroits front and rear and matched them up with 5.38 gears. They're the lowest available for the high-pinion 60. With our automatic overdrive tranny and 37-inch tires, it's the perfect setup for highway and off-road use. The people at Dynatrac told us the most common mistake customers make when ordering an axle is not going with a low enough gear ratio.
In today's Jeeps with overdrive trannies, you can easily get away with 5.13s or 5.38s spinning 35- or 37-inch tires. A 4.10:1 or 4.56:1 ratio will leave your Jeep seemingly underpowered and you shifting through the tranny searching for the right gear. Lower gears not only compensate for the larger rolling radius of the tires, they compensate for the extra weight, parasitic tire friction, and added wind resistance.
Factory TJ Wrangler housings measure in at 60 1/2 inches wide between wheel-mounting surfaces. To keep the 37s out of the suspension and sheetmetal when turning, we opted for a measurement of 63 1/2" on both front and rear axles. The extra 1 1/2 inches on each side help provide more articulation and increase stability.
Almost any lug pattern can be drilled for your axles. We went with the most common, which is the older Jeep/Ford/Dodge 5-on-5 1/2 lug pattern. Some people lean toward 8 lugs, but that's really overkill on a Jeep. Eight-lug hubs are more for 3/4- and 1-ton trucks that haul dirt or bricks. The same goes for rear full-floater axles. It's really an unnecessary extra expense and weight penalty.
Speaking of weight, we decided to throw the stock axles and the Pro-Rocks on a scale to see how much weight we gained in the swap. A stock TJ Dana 44 rear axle tips the scales at 221 pounds versus the Pro-Rock 60's 338 pounds. Up front the factory TJ Dana 30 weighs in at 238 pounds and the Pro-Rock front a portly 473 pounds. Overall, the axle swap only added 352 pounds to our Jeep. That's less than what we added by switching from 30-inch tires to 37s. Besides, the added weight complements stability by lowering your Jeep's center of gravity to help prevent rollovers. Reducing unnecessary weight is a good idea, but a well-designed, heavier axle that always performs is better than a lightweight axle that breaks down frequently.
Our Unlimited's axles were built with 40 splines in mind. In reality 40-spline shafts are probably overkill for most of us. However, it sure is nice to have it as an option, even if only in the future. You can upgrade your 35-spline Dynatrac axles to 40 splines with bolt-on parts! In the rear all that's required is a 40-spline carrier. The 40-spline semifloat shafts and bearings bolt right into the Dynatrac housing ends. Up front you'll need a carrier, inner and outer shafts, spindles, wheel hubs, and locking hubs (not yet available) or drivers. When you step into the 40-spline competition-alloy front shafts, you are required to run CTM U-joints since a stock U-joint would ultimately be the weak link in the assembly. Dynatrac has a warranty it stands behind, so it's not gonna build you a stupid axle with an obvious weakness like that.