One tool that is helpful in diagnosing wheel bearings is a wired or wireless microphone/stethoscope that can be attached to a knuckle. Once an engineer-only tool, the prices for these microphone/stethoscopes have dropped dramatically.

[This article was originally published in 2020 by Trucks, Parts, Service. It has been updated to include more timely information.]

Badwheelbearing symptoms

Bearings also aren’t going to get far without lubrication. And lubrication isn’t going to last for the long haul without good seals.

At the heart of dependable wheel-end performance lies proper wheel bearing adjustments. TMC’s RP-618C, which was just revised in October 2021 and serves as the gold standard in making those critical adjustments that can improve uptime and the bottom line. Hartman quickly referred to those recommended practices, as did Keith Fally, STEMCO national OEM account and service manager.

If the growling noise were more noticeable in a specific gear range, a worn bearing in the transmission would generally cause the bearing noise. If the bearing noise is constant regardless of acceleration or deceleration and is approximately three times wheel speed in frequency, the faulty bearing would generally be found on the transmission output shaft or the driveshaft intermediate support bearing.

“I think the old days of not utilizing maintained and calibrated measuring and adjustment tools have gone by the wayside and a lot of the fleets value training,” Hartman says. “They want to keep their technicians abreast of the latest training efforts and most of the manufacturers do supply that at no charge now because it’s so crucial to have that end-play dialed in within one- to five-thousandths of an inch if it’s a manually adjustable hub.”

“It’s also important to apply lubricant to the correct area of the wheel seal OD or ID of the seal before assembly. You should always follow the seal manufactures’ recommendations for the correct area of the seal to apply lube because if this is not done properly it can lead to a premature seal failure,” he adds.

Wheel bearing play can be measured with a dial indicator by placing the dial indicator against the hub and rocking the wheel in and out by hand. As a rule, you should see no more than .005” of play in the bearings if the bearings are good, but some specifications are so low that you can’t feel any play and won’t be able to measure it with a dial indicator. The improper installation of an axle nut is one of the most common causes wheel bearing comebacks. Most axle nuts should not be reused. If an old nut is used, it could work loose and destroy the preload of the bearing. When the preload is lost, the bearing will make a low frequency grumble. You can retighten the axle nut to see if the noise remains. Sometimes the noise will go away, but in some cases, the permanent bearing damage has already occurred.

“There are some manufacturers that don’t require any type of special tool,” Hartman says. “You can essentially use a hand tool like a rubber mallet. That negates some of those tool issues we see are in the market where people are using a block of wood, flat bar or something to put a seal in. It could do more damage to the seal unbeknownst to the end-user because they may not see it but internally the seal could be damaged from an improper tool being used.”

Wheelbearingnoisequick fix

“Check the condition of the spindle and the hub itself and make sure there’s no cracks and no deterioration. Then when you dock the hub assembly ensure that it's properly aligned without impacting the spindle and potentially damaging any of the components,” Hartman says.

Wheelbearingnoisewhen accelerating

While seal damage often conjures up images of techs hammering away on a block of wood, punch or some other object to seat seals into a hub, other lapses in judgement can lead to damage.

A popping or clicking noise when turning is a classic symptom of a bad outer CV joint. Also note the condition of the CV joint boot. If the boot is torn or leaking, it should be replaced regardless of the condition of the joint. If the CV joint is noisy, it needs to be replaced.

Of course, there’s a lot more to maintaining a smooth, safe ride than swapping out bearings and races. Tools, torque settings and lubricants all play vital roles. Reaching TMC’s recommended wheel bearing end play of .001- to .005-in. requires a calibrated dial indicator “with its magnetic base affixed to the hub or brake drum.” This isn’t boat trailer maintenance. Simply feeling out for bearing end play without a dial indicator is not recommended, experts say.

Wheelbearing knockingnoise

“We want to make sure before we inspect all the components themselves,” Hartman says. “Inspect the spindle nuts, no matter who manufactured them, inspect the threads to ensure they’re intact and not damaged or cross-threaded. Check the spindle itself. We want to make sure that it’s properly threaded and that there’s no cross-threading and no missing threads.

“The number one reason for a premature seal failure may be caused by a combination of improper bearing adjustment, improper or incomplete seal installation (always follow manufacturers' installation and pre-lubrication recommendations), not installing the hubcap correctly and not cleaning the spindle end, bearings and hub properly,” Fally says.

“Common missteps during bearing adjustments might include improper tightening, not checking end-play, not installing the axle fastener correctly or completely, not spinning the hub to set the bearings and not following the TMC recommended guidelines,” Fally says.

Though thankfully not as dramatic, other signs of wheel bearing failure include excessive heat, noise, reduced fuel economy and wheel wobble, Fally says.

Wheelbearingnoisetest

The improper installation of an axle nut is one of the most common causes wheel bearing comebacks. Most axle nuts should not be reused. If an old nut is used, it could work loose and destroy the preload of the bearing. When the preload is lost, the bearing will make a low frequency grumble. You can retighten the axle nut to see if the noise remains. Sometimes the noise will go away, but in some cases, the permanent bearing damage has already occurred.

“We have, at SKF, a complete lubrication validation department with our rubber engineering. Every time we meet with a specific fleet or an OE that wants to use a specific lubricant, we actually take that and run a compatibility test with it because we don’t know how types of types of lubricants are going to interact with certain rubber,” says Hartman.

Bearings won’t get far without the proper lube and for that Fally pointed to TMC’s RP-631B which provides recommendations for wheel-end lubrication.

“If you over-tighten the bearings or adjust them improperly it can lead to an overheated hub assembly and burn up the wheel-end,” Hartman says. “If it’s too loose, you’re going to have damage to the bearing and you’ll also pull on the seal itself, which may potentially leak in the future and can lead to a safety issue because if a seal’s going to leak you could potentially lead to a thermal event.

Wheel-end integrity is vital to truck maintenance and repair because no fleet customer wants the costly and dangerous breakdowns that wheel-end failures can bring.

To check for play, raise the vehicle so the wheel is off the ground, then grab the tire at the 12 and 6 o’clock positions and move it back and forth. As a rule, you should not feel any play or looseness if the vehicle has sealed wheel bearing cartridges or hubs with sealed wheel bearing assemblies. On older vehicles with serviceable wheel bearings, a little play is normal, but a lot of play is not. Refer to the vehicle’s service specifications for the maximum amount of acceptable play.

Wheelbearingnoisedangerous

“Our families are riding along next to these commercial vehicles while they’re going down the roads at 80,000 lb., and we want to ensure the end-user knows how to do proper installations and the procedure because the adjustment is so crucial that it can’t be left to interpretation,” says Mike Hartman, SKF national account manager.

Frontwheelbearingnoisesymptoms

“There are multiple variations of every different type of rubber and how they react with lubricants can be unknown at times and that’s a problem,” he says. “So what we do is run compatibility tests and put them through, in most cases, this starts with a minimum of a 30-day immersion test, then a full testing period to make sure there’s no type of degradation of the product or any type of contamination that we see with result of a lubricant that’s going to effect the seal, which would denigrate the life of it.”

While there are no set specifications for noise or standardized mounting points for the listening device, it can allow you to compare the bearing on each side and compare while on a test drive. These devices can also allow you to eliminate components that could be the source of cyclical noises like CV joints, brakes and differentials.

Tires can cause cyclical noise if the bands have shifted or if there is a road force imbalance. Uneven wear due to alignment issues is another factor for noise. Worn or failed bushings can also cause cyclical noise to be transferred to the body and frame.

What does a continuously variable transmission (CVT) mean for technicians and import nameplate shops? On the maintenance side, a CVT transmission requires more or the same frequency of fluid and filter changes as a conventional automatic transmission, and many of the basic procedures are the same. On the diagnostic side, a CVT transmission is less complicated internally than a 6- or 9-speed transmission.

Fleets and repair shops can also refer to TMC RP631C on lube fills/procedures and RP624C on lubricant fundamentals, STEMCO advises

The classic symptom of a bad wheel bearing is typically a cyclic chirping, squealing or growling noise that changes in proportion to vehicle speed. The sound may disappear at some speeds or only occur at certain speeds. The noise may get worse when turning, or it may disappear momentarily. So, it’s difficult to make a diagnosis based on noise alone. Related Articles - Hydraulic Suspension Bushings - Brake Problems - Electric Power Steering Evolution Misdiagnosis The noise can also be misleading. A caliper that’s sticking or a brake pad that’s loose and dragging may make a metallic scraping noise as it rubs against the brake rotor. The frequency of the noise will also change in proportion to vehicle speed, but will often go away or change when the brakes are lightly applied. Noise that only occurs when braking is likely a brake problem such as worn pads, not a bad wheel bearing. Tires can cause cyclical noise if the bands have shifted or if there is a road force imbalance. Uneven wear due to alignment issues is another factor for noise. Worn or failed bushings can also cause cyclical noise to be transferred to the body and frame. Wheel bearing noises tend to travel through the drivetrain and exit through a transmission or engine mount that’s “grounding” the noise from the drivetrain to the chassis. This grounding effect causes a wheel bearing noise to be transferred far from its point of origin. For these and other reasons, it’s often very difficult to detect the early stages of wheel bearing failure. If the growling noise were more noticeable in a specific gear range, a worn bearing in the transmission would generally cause the bearing noise. If the bearing noise is constant regardless of acceleration or deceleration and is approximately three times wheel speed in frequency, the faulty bearing would generally be found on the transmission output shaft or the driveshaft intermediate support bearing. Wheel bearing hub unit. A popping or clicking noise when turning is a classic symptom of a bad outer CV joint. Also note the condition of the CV joint boot. If the boot is torn or leaking, it should be replaced regardless of the condition of the joint. If the CV joint is noisy, it needs to be replaced. Some worn wheel bearings can often be detected by rocking the vehicle from side to side at low speeds with the steering wheel. This technique tends to increase the load on the bearings, causing the pitted bearing to become noisier than usual. This test works better when the vehicle is warm and in a parking area or roadway with light traffic. One tool that is helpful in diagnosing wheel bearings is a wired or wireless microphone/stethoscope that can be attached to a knuckle. Once an engineer-only tool, the prices for these microphone/stethoscopes have dropped dramatically. While there are no set specifications for noise or standardized mounting points for the listening device, it can allow you to compare the bearing on each side and compare while on a test drive. These devices can also allow you to eliminate components that could be the source of cyclical noises like CV joints, brakes and differentials. On the Lift To check for play, raise the vehicle so the wheel is off the ground, then grab the tire at the 12 and 6 o’clock positions and move it back and forth. As a rule, you should not feel any play or looseness if the vehicle has sealed wheel bearing cartridges or hubs with sealed wheel bearing assemblies. On older vehicles with serviceable wheel bearings, a little play is normal, but a lot of play is not. Refer to the vehicle’s service specifications for the maximum amount of acceptable play. Wheel bearing play can be measured with a dial indicator by placing the dial indicator against the hub and rocking the wheel in and out by hand. As a rule, you should see no more than .005” of play in the bearings if the bearings are good, but some specifications are so low that you can’t feel any play and won’t be able to measure it with a dial indicator. The improper installation of an axle nut is one of the most common causes wheel bearing comebacks. Most axle nuts should not be reused. If an old nut is used, it could work loose and destroy the preload of the bearing. When the preload is lost, the bearing will make a low frequency grumble. You can retighten the axle nut to see if the noise remains. Sometimes the noise will go away, but in some cases, the permanent bearing damage has already occurred.

“It’s unfortunate people will use whatever they have to put a seal in. Most manufacturers specifically use their own tooling that’s designed to work with those types of seals for installation purposes," he says.

Wheel bearing noises tend to travel through the drivetrain and exit through a transmission or engine mount that’s “grounding” the noise from the drivetrain to the chassis. This grounding effect causes a wheel bearing noise to be transferred far from its point of origin. For these and other reasons, it’s often very difficult to detect the early stages of wheel bearing failure.

When you’ve docked the hub assembly on the spindle, always support the hub while you’re putting the outer bearing assembly in the assembly,” he says. “When you start your adjustment procedure, ensure you use the proper tools and follow the recommended procedure for the application, example being for a manually adjustable hub, you would use the RP-618.”

Wheelbearing replacement cost

“Lubricant integrity is critical to the function and durability of all wheel-end components,” Fally says. “STEMCO recommends frequent inspection of the wheel-end for lubricant contamination and/or water intrusion. STEMCO is committed to continually testing lubricants available to the heavy-duty trucking industry to support the best performing systems. We publish a regularly reviewed list of recommended wheel-end lubricants.”

When other components fail, like an alternator, starter, injector, injector pump or EGR valve, the wheels remain on the truck. Faulty injectors aren’t exactly racking up the sort of headlines that have attorneys drooling. Bearing failures, however, are a much different story because they can lead to a tragic and costly wheel-off incident.

“STEMCO is proud to partner with TMC in the constant development of their recommended practices for recommended wheel-end procedures and maintenance,” says Fally.

The noise can also be misleading. A caliper that’s sticking or a brake pad that’s loose and dragging may make a metallic scraping noise as it rubs against the brake rotor. The frequency of the noise will also change in proportion to vehicle speed, but will often go away or change when the brakes are lightly applied. Noise that only occurs when braking is likely a brake problem such as worn pads, not a bad wheel bearing.

As the engine moves from the effects of torque and as the suspension of a vehicle travels up and down, the angle of the driveshaft changes.

Some worn wheel bearings can often be detected by rocking the vehicle from side to side at low speeds with the steering wheel. This technique tends to increase the load on the bearings, causing the pitted bearing to become noisier than usual. This test works better when the vehicle is warm and in a parking area or roadway with light traffic. One tool that is helpful in diagnosing wheel bearings is a wired or wireless microphone/stethoscope that can be attached to a knuckle. Once an engineer-only tool, the prices for these microphone/stethoscopes have dropped dramatically. While there are no set specifications for noise or standardized mounting points for the listening device, it can allow you to compare the bearing on each side and compare while on a test drive. These devices can also allow you to eliminate components that could be the source of cyclical noises like CV joints, brakes and differentials. On the Lift To check for play, raise the vehicle so the wheel is off the ground, then grab the tire at the 12 and 6 o’clock positions and move it back and forth. As a rule, you should not feel any play or looseness if the vehicle has sealed wheel bearing cartridges or hubs with sealed wheel bearing assemblies. On older vehicles with serviceable wheel bearings, a little play is normal, but a lot of play is not. Refer to the vehicle’s service specifications for the maximum amount of acceptable play. Wheel bearing play can be measured with a dial indicator by placing the dial indicator against the hub and rocking the wheel in and out by hand. As a rule, you should see no more than .005” of play in the bearings if the bearings are good, but some specifications are so low that you can’t feel any play and won’t be able to measure it with a dial indicator. The improper installation of an axle nut is one of the most common causes wheel bearing comebacks. Most axle nuts should not be reused. If an old nut is used, it could work loose and destroy the preload of the bearing. When the preload is lost, the bearing will make a low frequency grumble. You can retighten the axle nut to see if the noise remains. Sometimes the noise will go away, but in some cases, the permanent bearing damage has already occurred.