Hub Assembly & Front Wheel Bearing Replacement

Unit Bearings Hub Assembly Hub Assembly Parts

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.

Unit Bearings Hub Assembly Rebuildable Hub

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.

Rebuildable Hub ...This nut threads onto the end of the outer stub shaft and helps hold t

Unit Bearings Hub Assembly Unit Bearing Hub

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...

Unit Bearing Hub 1. The first step is determining whether or not you have unit bearings o

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 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.
2. Unit bearings usually only fail when the seals are damaged and allow sand, mud, water,
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.
3. To remove the unit bearing on a Jeep, Dodge, or GM vehicle, you first need to remove th
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.
4. After removing the brake caliper and rotors and the large nut, remove the four bolts th

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.
5. An impact gun was used to break the nuts free. If you are lucky, the unit bearing will
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.
6. Our first attempt at removal involved trying to get the unit bearing to spin in the knu
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.
7. Finally we got medieval on that unit bearing with a two-jaw puller attached to the oute

Unit Bearings Hub Assembly Knuckle In Press

8. The unit bearing came apart but left its mounting side still in the steering knuckle. We removed the knuckle from the axlehousing. This is not possible when the unit bearing is in one piece, but with the splined outer section removed, we were able to remove the two ball-joint nuts and drop the knuckle off the axle. We put the knuckle in the press and applied enough pressure to finally press the rusted old unit bearing out. This can have dire consequences, as the knuckles can bend if the unit bearing doesn't come out. After we removed the unit bearing, we checked the knuckle for flatness with a straightedge on the unit-bearing mounting surface.

9. We ordered the new unit bearing as well as most of our brake parts from the online parts house RockAuto.com. The unit bearing had the same casting marks as the one we removed, so we felt confident that they were quality pieces.
9. We ordered the new unit bearing as well as most of our brake parts from the online part
10. If you buy a new truck with front unit bearings (especially a Dodge truck) and you live anywhere rust is prevalent, then it's a good idea to remove the unit bearing and add antiseize to the mating surfaces as soon as possible to make any future disassembly easier. Remember that jobs like changing gears or fixing broken U-joints or axleshafts will require removing the front unit bearings, and if they can't be pulled out later without destroying them, you may need to replace them even when the unit bearing is still good.
10. If you buy a new truck with front unit bearings (especially a Dodge truck) and you liv
11. We cleaned the knuckle before assembly. First remove the axleshaft and line up the knuckle with the ball joints. Getting the ball-joint nuts installed requires an Allen wrench to keep the ball joint from spinning while tightening down the nut with a wrench.
11. We cleaned the knuckle before assembly. First remove the axleshaft and line up the knu

12. Start the four mounting bolts into the unit bearing (using thread locker for a secure attachment), and slowly pull the unit bearing into place evenly. Follow your service manual for prescribed torque settings.
12. Start the four mounting bolts into the unit bearing (using thread locker for a secure
13. The next-to-last step is installing the big axle nut and cotter key. Again, torque to spec as per your service manual.
13. The next-to-last step is installing the big axle nut and cotter key. Again, torque to
14. With the unit bearing replaced, we installed new rotors and calipers from RockAuto.com as well as some performance brake pads from EBC. Use the brakes gently for the first few days of driving to properly seat.
14. With the unit bearing replaced, we installed new rotors and calipers from RockAuto.com