This article was originally published Sept. 14, 2015. Some of the information may no longer be relevant, so please use it at your discretion.
Doesn’t it seem that it is the routine stuff we seem to make the most mistakes on? In our business, repetition can breed apathy and apathy leads to short cuts that can impact the quality of our work and the longevity of our repair. The funniest part (to me anyway) is that when a job improperly done comes back, it’s always the fault of the part we installed.
Over the last few years, I’ve had the opportunity to meet and talk with experts in a variety of areas and have learned much about how making just small adjustments in the repair process can drastically improve the overall quality of the work being done, and when the quality improves, customer satisfaction improves, and that means they stay with you and spend more money. It’s a win-win!
This month, I dive into a common repair – the inspection, service and replacement of hub bearings. I asked the folks at Federal-Mogul (MOOG), Timken, SKF and the Schaeffler Group (FAG) to share their expertise with me, so I could share it here with all of you.
Symptoms of a worn bearing
The most common indication of a worn or damaged hub bearing is noise. The noise can best be described by your customer as a snapping, grinding, knocking, or growling sound. Many suspension and tire issues can mimic these sounds, and one key in isolating the cause as a bearing fault is a change in the sound when the vehicle is turned, accelerated or decelerated.
Worn bearings also cause excessive endplay in the wheel assembly. This endplay can result in erratic or missing wheel speed sensor signals, uneven brake and tire wear, and (in a worst case scenario) could lead to a catastrophic failure that would allow the wheel to separate from the vehicle, but you need to, wait for the bearing to fail entirely to see the signs. Checking the bearing condition should be a part of any routine safety inspection you perform. The “Garage Gurus” at Federal-Mogul suggest you inspect suspect hub bearings using this method:
To inspect the hub assembly, raise the wheel-end off the ground and see if the wheel rotates freely. Any noise or resistance is a common sign of trouble. Next, while holding the tire at the 9 and 3 o’clock positions, try to pull and push the wheel end as you rotate the tire to the left and right. Then, do the same while gripping the tire at the 6 and 12 o’clock positions. Any play or looseness in the wheel-end while performing these tests confirms that the customer needs a new hub bearing assembly.
In the days when tapered wheel bearings were the norm, we all knew we had to set the bearing preload by first setting the bearing and then backing off the wheel nut, followed by tightening the wheel nut to a specified torque. Hub bearings also have a preload specification, and either type of bearing can be checked even more closely by the method suggested by Timken’s Rick Domin:
"You should measure the endplay of the hub assembly by placing a dial indicator on the knuckle and indicating on the hub face, and push and pull on the hub flange and measure the total indicator movement. You should refer to the vehicle manufacturer for specifications. Next look for signs of excessive grease coming from either side of the bearing indicating that a seal is leaking and allowing the grease to be flung from the hub. If the seals are letting the grease out of the bearing, then contamination can get into the hub as well. Moisture inside the bearing will drastically shorten the life of any bearing. The moisture can corrode the bearing surfaces and create debris inside the hub in the form of rust, which will shorten the life of the bearing."
You’ll find that the specifications that Domin is referring to are often listed in thousands of an inch, and that small a deviation will not readily be felt by simply shaking the tire alone, but it can be enough to set an ABS system DTC and any play in excess of that specification is sufficient reason to recommend replacement.
Bearing replacement
Older hub bearing-equipped models had replaceable bearings but later model designs have moved in favor of replacing the entire hub assembly. This makes it more convenient for the technician and helps prevent damage to the bearing assembly caused by improper replacement methods.
Schaeffler’s Mike Geul offers this advice when replacing the bearings themselves:
Press fit wheel bearings with separate hubs can be serviced on the car using a hub tamer tool kit or by removing the suspension knuckle from the vehicle and using a floor-mounted hydraulic press. This style wheel bearing is more difficult to replace and can be labor intensive. Best practices apply when using heat and penetrating fluid to aid in separating components. Use common sense. Do not overheat the knuckle as it will distort. It is also recommended that a new hub be installed when replacing press fit style bearings. Many times, wheel hubs have been damaged during the removal process of the bearings as the bearing races separate. This usually leaves an inner bearing race on the hub that becomes difficult to remove.
After the old bearing is removed, clean the suspension knuckle and snap ring groove, if one is present. When using a floor mounted hydraulic press, be sure that all components are level. Make sure that the new bearing is facing the correct direction. Some bearings have an internal tone ring for a wheel speed sensor. Press on the outer part of the new bearing, not on the inner race as it will separate and damage. If the new wheel bearing is not being pressed in straight, do not over-press the bearing. Over-pressing will damage the new bearing. Stop! Reset the bearing and level the knuckle. When the new bearing is installed the hub needs to be pressed into the bearing. It is very important to fully support the complete bearing on the opposite side of the hub that is being pressed. This will help to ensure that the new hub is being pressed into place correctly.
All the company experts I spoke with stressed the need to clean the inside of the knuckle where the new bearings are going to go, including the groove for any snap ring used. Failure to do so could lead to premature failure of the bearing. Another point offered by more than one source was to avoid using an impact gun on the axle nut to avoid damaging the spindle threads, and to use a new axle nut when reinstalling the assembly.
As for hub assemblies, here’s what the Gurus at Federal-Mogul had to say:
For installation of the new hub assembly, first make sure you have a clean, flat mounting surface for precise seating and alignment. Use a wire brush to remove any burrs or loose metal from the knuckle. Even small imperfections can cause unwanted problems, so give the mating surface a good cleanup before installing the new bearing assembly.
Now guide the new hub assembly onto the knuckle. It’s critical to make sure the new unit is properly aligned with its mating surface before attaching and torqueing the mounting bolts.
If the vehicle has anti-lock brakes, attach the ABS connector and then check system operation by turning the key. The next step is to torque the hub assembly mounting bolts to the manufacturer’s specifications. You must use a torque wrench.
Now reassemble the brake rotor and caliper, and install a new axle nut, once again using a torque wrench to match the manufacturer’s specs. Do not use an impact wrench.
And finally, reinstall the wheel, hand-tighten the lug nuts and then torque them to spec when the vehicle is back on the ground.
Are you picking up the same vibe here as I am? All of our experts stressed how important it is to torque component fasteners, especially the hub assembly mounting bolts and even more critically – the axle nut. Why?
The answer lies in the question I asked all of the experts - “What is the most common mistake you see being made?” Here are some of the responses I got:
A wheel or hub bearing that has been returned under warranty is typically found to be defective due to improper installation. A common cause is the axle nut being over-torqued. This can cause excessive load and over-compress the new bearing. Tightening an axle nut with an impact wrench can also have the opposite effect and result in the axel nut being under-torqued.
Failure to follow the manufacturer’s installation instructions – particularly in setting bearing preload – is by far the most common error and can have a direct impact on the performance, service life and, potentially, the safety, of the hub assembly.
The answer is improper installation. Most often, bearing preload was not set correctly, but there are a variety of other installation-related issues, including the improper use of an impact wrench rather than a torque wrench and reuse of the existing nut when installing the new hub assembly.
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Having worked under flat rate nearly my entire professional career, I certainly understand the reasoning to get things done as quickly and easily as possible. And so do the makers of the parts we use every day. Some new bearing designs offer preset bearing preloads and reinforced and redesigned electrical connections and harnesses to make life in the bay a little easier. And I admit – I made some of these common mistakes myself, from a lack of understanding on just how important those “extra” steps were. And now that you know, too,
I hope you’ll make a few minor adjustments in your hub bearing service techniques and do that routine job right the first time.
