Jeep Wrangler Unit Bearings: What You Don't Know Can Hurt You
The Jeep Wrangler is arguably one of the most capable 4x4 platforms of all time. The open-top and lightweight machines have proven to be exceptionally nimble and competent wheelers time and time again. The official Wrangler designation for the two-door Jeep was adorned in 1987 with the Jeep Wrangler YJ. The leaf-sprung suspension and square-headlight grille of the YJ seems almost archaic compared to today’s Wrangler, but it was an impressive offering for the time. While the initial Wrangler had a few issues here and there, it was a major leap forward in engineering from the previous CJ model. One of the fresh Wrangler attributes in 1987 was the high-pinion Dana 30 front axle, which shared components with the Jeep Cherokee XJ. Of these shared front axle parts one of the most significant was sealed unit bearing. This all-in-one hub-and-bearing assembly did away with the traditional spindle bearing setup. The unit bearing and traditional spindle bearing setup both use a two bearings per assembly, the major difference being the distance between the two bearings. In a unit bearing, they are paired closely together. In the spindle configuration, they are farther apart, which helps when adding larger tires with off-set wheels. Since the unit bearing is non-serviceable, frequent time in the mud and sand could mean replacing the entire unit entirely, which can get expensive. The idea was to have an easier to package and replace wheel bearing end that wouldn’t require a service throughout its lifecycle. This all-in-one unit not only did away with the traditional spindle, but the selectable hub feature as well. This meant you no longer had to exit the vehicle when you wanted to engage the front axle. Although it was a more user-friendly design, some of those convenience features came at a cost. Taking away the ability to disengage the hubs added a layer of complexity if you did happen to break a front axle component on the trail. Since the splined inner hub used the stub shaft and axle nut as a retaining feature for the bearings, you couldn’t simply remove the axleshaft on the trail and drive home. This full-hub engagement also meant the front end components were always rotating, adding increased wear and drag on the vehicle. In an effort to reduce drag and increase fuel efficiency, the ’87-’95 Wrangler’s Dana 30 front axle was fitted with a two-piece passenger side front axleshaft. When you engaged the transfer case, a vacuum-actuated collar united the two ‘shafts. This design was notoriously problematic and went away in 1997. Obviously, having two platforms sharing components made sense on paper, and by the time the YJ was unveiled, the XJ had already proven the unit bearing’s worthiness for nearly four years. The unit bearing remained essentially unchanged on the Wrangler until the launch of the redesigned JK series Wrangler in 2007. The new unit bearings had a few improvements, but one was paramount over the outgoing unit. This was the captured bearing flange. The captured bearing on the JK unit bearing doesn’t require the axleshaft and flange nut to be secured to the hub for you to drive down the road. This is significant. Why? Well, the ’87-’06 Wrangler unit bearing would literally come apart if you tried driving on it without the stub shaft and axle nut to secure it to the hub. Sadly, this isn’t something that all wheelers know out of the gate and has been the cause of multiple on- and off-road accidents. Since the new style JK unit bearings are fitted with a 5-on-5 wheel bolt pattern, not a 5-on-4.5 like the previous generation YJ and TJ models, simply swapping the newer style bearing over isn’t an easy task. Along with completely different steering knuckles and tone rings, retrofitting the new style hub to an older style Wrangler axle wouldn’t be worth the trouble and investment. So, what’s the take away here? If you break a component (axleshaft, ring-and-pinion, U-joint, so on) on a ’07-current Jeep Wrangler JK, you can safely remove the axleshaft and get back to civilization. If you happen to break something on a YJ or TJ Dana 30 or Dana 44 (Rubicon TJ only) front axle, we strongly recommended carrying an extra stub shaft and axle nut at the very least to get your broken rig off the trail safely. Speaking of things to carry, you’ll need a 36mm for the ’87-’06 front axle nut, and a 35mm for the ’07-current JK model.