Photography by Harry Wagner
One of our favorite attributes of the Jeep Wrangler JK and JL is the huge fender openings that allow you to run 37-inch tall tires with only a modest lift. Lower lift heights mean less time and money need to be spent on longer control arms, extended brake lines, and track bar drop brackets. The flip side is that while it is easy to fit those big tires, your axles might not live a long life as a result of the extra weight and leverage of big tires, particularly if you have a heavy Jeep or subject it to hardcore wheeling on a regular basis. This poses the question about what to do next? There are three basic options: Upgrade your factory axles, build junkyard axles, or order crate axles. We will discuss each in greater detail here with the advantages and disadvantages.
JK Wrangler front axles have a reputation for bending, so the addition of a truss, such as those from Synergy Manufacturing, are a good addition before you bend your axle. While the truss itself is relatively inexpensive, installation can be expensive as the welding required is quite involved.
Upgrade Your Factory Axles
The JK Wrangler came with a Dana 30 front axle and Dana 44 rear axle on Sport and Sahara models and Dana 44 axles front and rear on Rubicon models. For the JL Wrangler, Dana refers to the axles as AdvenTEK M186 in front and AdvenTEK M200 axles for the Sport and Sahara and M210 front and M220 rear axle, with the number representing the ring gear size in millimeters. These axles can be built to reliably run 37-inch tires with the appropriate upgrades. The ring and pinion, brakes, and unit bearings are all larger than past Dana 44 axles. Rubicon axles come from the factory with electric locking differentials, but the addition of American-made G2 Placer Gold chromoly axle shafts will provide an extra level of strength. On the JL Wrangler, adding aftermarket axle shafts also gets ride of the failure prone two-piece axle shaft in the Front Axle Disconnect (FAD).
If you buy a junkyard axle, plan to upgrade the differential, ring and pinion, and axle shafts along with wear items like brakes and ball joints. These costs should be considered when considering your options. If you have the mechanical ability to install these parts yourself you can save a lot of money over a crate axle, but if you are paying for labor it might make economic sense to buy a complete axle assembly.
Build Junkyard Axles
For decades, Jeep owners have been retrofitting axles from one ton trucks to run big (think 40-inch tall) tires. In the 80s, the Big Three all used solid axles under their heavy duty trucks, but these days the most popular junkyard axles to swap under a Jeep are from a Ford Super Duty due to their abundance. These are generally referred to as 99-04 and 05+ axles, with the newer axles having larger unit bearings, brakes, and stub shafts. The front axles are Dana 60s from 99 to current, although watch out for some oddball Dana 50s in older Super Duties. The rear axles are Sterling 10.5 that match the width (72 inches) and bolt pattern (8×170) of the front axle. One of the biggest issues with retrofitting Super Duty (or other) axles under a JK or JL is the mounts for the coils, control arms, shocks, track bar, and sway bars. Artec makes a kit that takes the guesswork out of swapping a Super Duty axle under your Wrangler and is perfect for the guy who wants to build his Jeep at home in the garage.
One of the best things about the Wrangler platform is the plethora of aftermarket support. There is an abundance of crate axle assemblies that will bolt right in to your JK or JL Wrangler from Currie Enterprises, Teraflex, Dynatrac, and more. Many of these aftermarket housings are designed to maximize ground clearance beyond what you can get from a junkyard axle.
Order Crate Axles
Crate axles are not inexpensive but they are the quickest way to get back on the trail without concerns of breakage. We recommend upgrading both axles at the same time to match the widths and bolt patterns front to rear. That way you don’t end up with a semi-float rear axle when you would rather have a full float eight lug axle in the future. Full-float axle assemblies use a hub in the rear (similar to a front axle but it does not providing turning) so that the axle shaft only has to transfer power, not hold the vehicle upright as well. Adding wider axles allows you to turn a larger tire to full lock before hitting the frame or suspension components, all while maintaining proper scrub radius that can be compromised by running wheel spacers or wheels with shallow backspacing in order to gain track width.
TeraFlex, Currie, and Dynatrac all offer complete axle assemblies that will bolt into the JK and JL Wrangler platforms. These companies have solved the issues with tone rings, wheel sensors, and mounting brackets to make installation straightforward. They can also be ordered with your choice of gear ratio and differential, products that you would need to purchase and have professionally installed in junkyard axles. If you don’t have the resources to build axles yourself, the cost of junkyard axles can equal or surpass the cost of crate axle assemblies by the time you have added all of these parts.
There are a variety of junkyard axles that can be adapted to a Wrangler, but don’t let the low initial purchase price lure you in. Mounts, seals, bearings, differentials, and ring and pinion should all be added to your budget, not to mention the labor necessary to install these parts if you are not going to do it at home.
Bigger axles are just part of an equation that often includes aftermarket suspension, larger tires, beadlock wheels, hydraulic assist steering, and more. Fortunately, your factory axles and other stock components can often be sold to offset some of the expense.
Steering is another area that will need to be addressed with aftermarket axle assemblies. Assuming they are wider than stock, you will need a longer tie rod and drag link. And if you are turning 40-inch tires plan to add hydraulic assist such as this kit from PSC to your list of upgrades.
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