Where there are spinning automotive parts, there are almost always lubricated bearings involved. At least we hope they stay lubricated and spinning. Front wheel bearing failures are something we have to deal with more frequently than your average motorist. We use larger tires, often with greater offset wheels, and load the spindles harder in the dirt. However, poor installation of wheel bearings can cause premature failure as well.
When replacing front wheel bearings, a little bit of attention to detail can optimize their longevity. Tapered-roller bearings are tensioned by the installer using a spindle nut, while unit (or cartridge) bearings preload themselves relying only on you to properly tighten a high-torque spindle nut upon assembly.
Traditional front axle assemblies, and rear full-float axles, typically use a set of tapered-roller bearings on the spindle that mate to a set of tapered races pressed into the wheel hub. Once the bearings are slipped on with the wheel hub, a flat washer and a hex nut follow. This first nut sets the bearing preload tension. A second washer is then installed and it has some means of locking the position of the preload adjustment nut. Finally, a second nut is installed and tightened to secure the entire assembly in place.
You will generally tighten to the specified torque reading, and may advance or retard from that if needed to align the nut for use of a cotter pin. Some manufacturers may have special wheel bearing adjustment sequences. We’ve seen instructions to tighten to a torque spec then rotate the nut a fixed amount further, tighten-loosen-tighten sequences, and other means to get to the final setting.
In any case, it’s generally a good idea to turn the wheel hub a few times while tightening the nut to ensure the bearings are seating evenly well. Since proper torque procedures vary widely for wheel bearing assemblies, the safest bet is to look up the recommended preload technique. Some manufacturers recommend the tire be on the ground for final torque setting while others specify the tire be off the ground.
Some front wheels hubs are sold as a complete cartridge or unit bearing assembly, such as this one from a Dana straight axle. These simply bolt to the outer knuckle assembly so there is no bearing setup or preload involved with installing a bearing assembly such as this. This type bearing is also factory greased and not serviceable. Once a bearing is worn or damaged, the entire assembly must be replaced.
When replacing tapered-roller bearings, you’ll need to also remove the outer races from the wheel hubs. These can usually be knocked free from the hub with a steel rod and hammer. Installation can be done in reverse, but using a brass drift, or aluminum bearing driver, to drive races back into the hubs without causing damage to the precision race surfaces.
Note too that wheel bearing wear or poor adjustment can affect disc brake performance. When there is excessive play in a wheel bearing it can allow rotor wobble that can push the brake pad and caliper piston back into the caliper body. Braking will then feel spongy on first pedal application and you may get full braking only after a second pump of the pedal.
Some 2WD Ford F-150 trucks have a unit bearing pressed into a wheel hub with an integrated brake rotor. In some cases, such as on this Ford F-150 front wheel hub, the assembly is serviceable and replacement bearings are available separately. On newer cartridge type wheel bearings, a worn bearing may cause a speed sensor error code related to the ABS module due to an erratic signal from the speed sensor at that wheel hub.
Unit bearing assemblies are designed to be correctly preloaded by accurately torquing the wheel hub nut on the spindle. Manufacturers warn of premature bearing failure if not torqued to the proper value. We’ve seen mechanics zip the spindle nut on with a big air impact tool. However, use of an impact gun is not recommended as it can shock load the CV joints on a drive axle or damage axle threads. Some spindle nuts are also single-use items and are meant to be replaced with a new one once removed.
There are times when you need to pull a bearing off an assembly, but either don’t have the proper bearing puller, the bearing cannot be grasped well enough to pull it free, or a slip fit bearing has been overheated and its inner race is frozen onto the spindle or other shaft. A solution we’ve used is to take a cutting disc on a rotary tool or hand grinder, and place one or more notches in the inner bearing race after removing the cage and rollers. A smack or two on a notch with a cold chisel should fracture the race and allow for its removal. We once removed a frozen wheel bearing race on a truck spindle on the side of the highway using a hacksaw and chisel. It was super slow, not fun at all, but it did eventually work to get the race free.