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.
Unit Bearing vs. Standard...
Unit Bearing vs. Standard Bearing
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.
Tapered roller bearings are...
Tapered roller bearings are designed to converge at a common point. When that point or axis is modified, it upsets the geometry of the bearing. When you increase the offset of your wheel and enlarge the diameter of the tire, it upsets the original bearing preset and compromises the unit's strength, thus resulting in premature wear and possible failure.
One of the most obvious differences...
One of the most obvious differences between the unit bearing and the traditional spindle bearing setup is the complete absence of the spindle. Removing the spindle allows manufacturers to create a simple and efficient bearing package. This also eliminates the need to adjust bearing preload and allows for an easier teardown of the frontend that doesn't require any special tools.
Many unit bearings use a single...
Many unit bearings use a single axle nut to disconnect the axleshaft from the hub. On most Jeep applications you need to remove the unit bearing to gain access to the shaft, but on many IFS applications you can remove the shaft with the bearing still intact, making for an easy trail fix. Does that give IFS a couple of cool points? Nah.
The old-style spindle bolts...
The old-style spindle bolts to the knuckle with the axleshaft going through the spindle. The vehicle hub and bearings slide over the spindle and are adjusted by nuts and washers to a specific preload.
Modified unit bearings such...
Modified unit bearings such as this F-450 hub assembly are becoming more popular in the aftermarket world and are used by axle building companies such as Currie and Spidertrax. These companies use the larger units for their strength and availability. The abuse that the bearing may see in an off-road application is actually easier on the bearing when compared to the heavy use and weight that they are originally designed for. Another big plus is that they can be mated with many of the aftermarket selectable hubs to give you the option of manually engaging the front axle.
Wheel spacers can be a great...
Wheel spacers can be a great asset to keep your rig stable off-road, but when used in conjunction with large tires and a unit bearing they can double the amount of stress on your front end. The same theory goes for wheel offset; the less backspacing you have, the greater the leverage that you put on the bearings.