Unit Bearing Basics
Do you remember a time when wheeling meant jumping out of your 4x4 onto the dirt and manually locking in your front selectable hubs? A time when mud dripping off your wheels equaled a few hours in the garage keeping your front wheel bearings greased and running smoothly? Nowadays with the push of a button or an easy pull of a lever, wheelers can spend all day in the dirt without ever feeling the rich ground beneath their feet since selectable hubs are severely out of fashion with the advent of the unit bearing. So what's the difference between these late-model 4xs and their nonselectable hubs and unit bearings for the front wheels instead of traditional bearings?
The unit bearing has been around a long time, probably longer than many of us have been around. Its simple packaging and efficient design have allowed it to creep its way into most late-model 4x4 applications around the world, making it standard equipment on everything from the new Jeep Wrangler to the beefy 1-ton trucks.
The unit bearing uses a simple opposed dual-bearing system that is preloaded to factory specifications as a unit with the vehicle hub (hence the name). What this means to you is no more packing bearings, adjusting preload, or hub tools to deal with. Though these units are nonserviceable, they are slated for long-life intervals and we've seen some that have lasted more than 150,000 miles on stock applications. Using a splined centersection, the inner part of the unit bearing serves as a fully engaged hub, which causes the front drivetrain components to constantly rotate. This feature allows manufacturers to eliminate the need for a selectable hub and create a smaller package that works on both independent and solid-axle applications.
The old-style spindle and hub setup requires specific adjustment for the bearings and is not sealed as well as the unit bearing design. However, parts are easily available should something break, and the through-spindle design for the axleshaft makes it easy to fit selectable hubs on this style.