What to Watch for with Wheel Bearings

[Counterman]

Long before sealed wheel bearings became part of the auto repair landscape, many of us clocked countless hours cleaning and repacking tapered roller bearings. When it was time for installation and tightening the wheel bearing nut, we referred to the process as “adjusting the wheel bearings.” We knew if we didn’t do it right, they would be too loose or too tight. If they were too loose, the excessive end play could cause alignment and braking problems, as well as accelerated wear on the bearings due to an uneven load distribution on the rollers. If they were too tight, the bearings would run hot, and it wouldn’t take long before the excessive heat would cause the metal to break down.

What we were actually doing was setting the pre-load. We did it by hand and perhaps these tapered wheel bearings offered just a bit of forgiveness to allow for human imperfection, but today, tapered roller bearings are almost a thing of the past for everyday repair shops and when we replace wheel bearings, we are working with the Generation 1, 2 and 3 sealed wheel bearings. Preload, which controls bearing geometry, is more critical than ever.

Almost all the Gen 1, 2 or 3 bearings utilize balls as opposed to rollers. Roller bearings have the advantage of a much greater contact area between the rollers and races, and therefore can support a heavier load. With use, they can develop a slight amount of play, but due to their contact area and load distribution, it didn’t have much of an effect. As long as they were cleaned, repacked and adjusted on a regular basis, they would last a long time.

Ball bearings, on the other hand, have a very small contact patch with the race. When the pre-load on these bearings is correctly set, then the geometrical relationship between the races and the rolling components is set.

The pre-load determines the exact location at which the roller balls will contact the inner and outer races. This is critical because modern vehicle suspension and steering can no longer be viewed as separate vehicle systems. They work in unison with antilock braking systems (ABS), traction and stability control and advanced driver assistance systems (ADAS). Not only must bearing pre-load be correct to avoid premature wear, but it is critical for handling and braking, as well as providing the correct alignment to ABS sensors that are built in or mounted to the wheel bearing assembly.

Setting the pre-load on Gen 1, 2 or 3 wheel bearings is a different process, but simpler, at least from the process standpoint. There’s one step. Torque. Gen 1 bearings press into the steering knuckle, and this style of bearing certainly caused a few headaches to all of us until we became familiar with the requirements for replacing them. Gen 1 bearings have no pre-load when they are manufactured. Not only must you use the correct procedures for pressing them in to prevent damage, but they require either a spindle or axle shaft through the center that is used to set pre-load, and just simply hold the whole thing together.

The torque specification on the thru-shaft is generally a very high torque, and the torque must be set before putting the weight of the vehicle on the ground. If weight is put on the bearing prior to torquing it, the races and rolling components will be wedged out of place, preventing the torque from drawing everything into the proper geometrical alignment.

This was a mistake often made, as well as using an impact wrench to tighten the nut or bolt. The most common methods developed to torque Gen 1 bearings properly are, one, to wedge a long prybar between the lug studs to hold the hub while torquing. This often requires help of another person. And, two, if you have vented brake rotors, to slide a tapered punch into one of the vents and allow it to rest against the brake caliper bracket as you torque the nut.

Most of the time, manufacturers gave us only the torque specification, but no tips for attaining it safely, so we had to devise our own methods. I still always look at the specific procedure for any given vehicle, since it’s such a critical setting, and that’s always the best advice. Some thru-shaft bolts are torque-to-yield bolts, and they require an incredible amount of force to reach the specified setting.

In some of these cases, I’ve seen manufacturers specify an initial torque specification to align the bearing geometry, then to set the vehicle on the ground to perform the “stretching” of a torque-to-yield bolt. Even then, it required a floor jack handle on the end of a breaker bar, and the help of another person to reach the specification, all the time cautiously leaning away in hopes the breaker bar doesn’t snap like a toothpick.

It is this one particular fastener that has led too many an auto technician to buy a few ¾-inch drive sockets and ¾-inch breaker bar; tools normally associated with heavy equipment and semi-trucks.

Gen 2 wheel bearings have a flange or hub pre-installed, and Gen 3 wheel bearings are a complete hub/mounting flange unit. These bearings are easier to install (at least in theory…but that’s a whole other story), yet the torque specification is just as critical, and that goes for the mounting flanges as well as a thru-shaft fasteners.

Some of these bearings are manufactured utilizing a process called roll-forming or orbital forming that sets the pre-load, but this is not always the case. If the bearing is for a non-driven application, and there is no thru-shaft, then you know this is the case. Anything that has a thru-shaft, regardless of the manufacturing and whether a pre-load is set, relies on the proper torque to set or maintain the proper pre-load and bearing geometry.

The bottom line: Always follow manufacturer instructions to avoid problems. This is the best advice for your customer, because most wheel bearing warranty issues are caused by incorrect installation.

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