Last month we showed you the basic steps to repack front wheel bearings in all their greasy glory, but not every 4x4 has rebuildable front bearings. The nonserviceable front hubs are commonly referred to as unit bearings or, more technically, the axle bearing and hub assembly. These are a factory-built piece with two bearings and race assemblies already installed and packed with grease. We like unit bearings for their ease of assembly (at least in theory, as you'll see in the photos) and the fact that there is no greasy mess required. The unit bearings are machine assembled to extremely high tolerances and engineered with better seals and bearing life in mind compared to the older serviceable bearing hub design. However these same traits mean that if the unit bearings should start to, or completely, fail you must replace the entire unit, whereas a properly serviced older-style hub bearing like we showed you last month can last at least as long (if not longer) with proper maintenance. These unit bearings can cost well over $200 each, while servicing your rebuildable hubs takes only the cost of parts cleaner, grease, and a new hub seal if the bearings are still good. If the bearings are not good, you'll still spend less than $100 per wheel end.
Another issue we have with most unit bearings (Dodge, GM, and Jeep) is that most of them do not allow for a selectable front locking hub (late-model Ford Super Dutys do have selectable or vacuum-controlled hubs), and this means that as you drive down the street you are spinning all your internal axleshafts and front differential, which in turn saps your mileage and fuel economy. There are kits available from Dynatrac and Solid Axle that replace common unit bearings with a rebuildable hub and selectable hubs, but these require a fair bit of mileage to recoup the costs depending on the price of fuel.
Rebuildable Hub ...This nut...
Rebuildable Hub
...This nut threads onto the end of the outer stub shaft and helps hold the unit bearing together. If there is a large hub sticking out of your wheel center, then you most likely have a rebuildable front hub.
Unit Bearing Hub 1. The first...
Unit Bearing Hub
1. The first step is determining whether or not you have unit bearings or rebuildable hubs on your front axle. A unit-bearing axle (top) has a large nut that most likely has some sort of cotter pin keeping it from backing off...
Sometimes it's just easier to simply replace worn unit bearings with replacement parts. That is our plan for this month's back-to-basics story. This repair/replacement should have been an easy job, which of course means it took us more than a week! Time was spent tracking down the parts (easy), beating the rusty old parts to oblivion in the removal stage (hard), and carefully putting it all back together again (easy).
2. Unit bearings usually only...
2. Unit bearings usually only fail when the seals are damaged and allow sand, mud, water, or grit inside, which contaminates the grease until it no longer lubricates the bearings. You may first notice a bearing squeal. Then if you lift the front axle and are able to wiggle the wheel when pushing in or out on the top and bottom of the tire, it's pretty likely that the unit bearing has failed and you need to replace it.
3. To remove the unit bearing...
3. To remove the unit bearing on a Jeep, Dodge, or GM vehicle, you first need to remove the big nut that screws onto the end of the axle stub shaft. The axles require a large socket, and some have a small cotter pin that holds the nut in place. Almost every nut on this Dodge AAM 9.25 axle also suffered from rust, so liberal amounts of your favorite lubricant nut buster are recommended.
4. After removing the brake...
4. After removing the brake caliper and rotors and the large nut, remove the four bolts that hold the unit bearing to the steering knuckle. We also removed the speed-sensor wire and sensor, but most new unit bearings come with a new sensor and wire. To help release the four nuts, we heated them up with a propane torch, then applied some wax to the bolt threads.
5. An impact gun was used...
5. An impact gun was used to break the nuts free. If you are lucky, the unit bearing will fall right out with a little hammer persuasion. We weren't so lucky.
6. Our first attempt at removal...
6. Our first attempt at removal involved trying to get the unit bearing to spin in the knuckle after applying more heat and hitting it with a hammer and punch, but this didn't budge the piece at all. Next we reinstalled the four mounting bolts and tried to pound the unit bearing straight out by pounding on the bolt heads. This is only recommended if you plan on replacing all the mounting bolts. Again, the unit bearing just laughed at us.
7. Finally we got medieval...
7. Finally we got medieval on that unit bearing with a two-jaw puller attached to the outer flange of the unit bearing and pushing against the axleshaft. This was going to have one of two results: It would either pull the unit bearing out of the knuckle, or it would tear it in two.