Your vehicle's wheels spin around an axle, allowing your car to roll along the road. The wheel hub is the mounting component at the end of the axle that holds the wheel in place. Inside that wheel hub is a bearing that allows the wheel to spin freely around the axle with as little friction as possible. This wheel hub bearing is a crucial automotive part that can greatly impact your driving experience if it fails.
What Is a Wheel Hub Bearing?
A wheel hub bearing is an integrated unit consisting of two main components:
An outer race: This stationary part mounts solidly to the wheel hub and essentially forms the “outer shell” of the bearing.
Inner race and steel ball bearings: The inner race fits over the axle and can spin independently of the outer race. Between these two races is a set of hardened steel ball bearings, usually between 7-15 balls held evenly spaced apart by a ball separator.
This whole assembly fits snugly but not too tightly inside the outer race, secured by a locking nut on one end. The steel balls rotate between the races, allowing the inner race and axle to spin freely within the outer race and wheel hub. A thin layer of thick grease coats the balls and races, lubricating the bearing to reduce friction and wear.
Sealed bearings have rubber seals built in to help keep dirt and moisture out of the races and grease. This sealing makes them more durable and longer-lasting than non-contact or open-wheel bearings.
Why Are Wheel Bearings So Important?
Wheel hub bearings are what allow your wheels to rotate freely at highway speeds with minimal heat and resistance. Without sound bearings:
Your gas mileage would plummet since friction would make the wheels more difficult to turn. The engine would have to work harder, burning more fuel to maintain speed.
The wheel ends would run hot and could severely damage the axle hub, wheel components, or brakes. Excess friction can easily produce hundreds of degrees of heat.
The wheels would make loud noises when turning, including squealing or grinding sounds. This audible feedback from strained motion is usually the first sign of a failing bearing.
Vibration would increase over time as the bearing components wear unevenly or spot-weld themselves together under heavy loads instead of rolling smoothly.
Uneven tire wear patterns like cupping across the tread can start to develop from play or wobble in a loose bearing. Too much runout can be difficult to balance and lead to a steering wheel shake.
Ultimately the bearing could seize up entirely, preventing the wheel from turning and making it very difficult to control the vehicle. Total failure usually happens without warning after an otherwise normal drive cycle.
Replacing bad wheel bearings before they fail keeps your family safe while saving money on avoiding unnecessary repairs or breakdowns. Don't ignore any suspicious noises or vibrations coming from a wheel end!
Symptoms Your Wheel Hub Bearing Is Worn Out
A worn out or damaged wheel hub bearing makes its presence known through several common symptoms:
Grinding Noise - Once grease starts to break down or ball bearings develop flat spots, a metallic grinding sound emanates from the failing bearing whenever you turn the wheels left or right.
Whining Pitch - Friction causing the bearing to stick somewhat as it rotates can create a high-pitched whirling sound that fluctuates with vehicle speed.
Popping / Clicking - Damaged or dirty bearings that catch while turning instead of rolling smoothly often make loud clicks or pops. This symptom tends to come and go.
Play In The Wheel - Grab each wheel at the 12 and 6 o'clock positions and attempt to rock it. If you detect any clunking or looseness, the bearings could be worn out. Bad tie rod ends or ball joints can mimic this feeling.
Vibration At High Speed - If the wheels seem to vibrate excessively above 50 mph, warped brake rotors are often the culprit. However, badly worn bearings can also shake and shudder on the freeway.
Leaking Grease - The rubber seals on sealed wheel bearings keep lubricant in place. If you spot grease slung around the edges of your wheels, the seals could be compromised.
Replacing Wheel Hub Bearings
Diagnosing which corner has the bad wheel bearing is easiest with mechanic's stethoscopes to pinpoint the source of any rumbling or mechanical noises. Replace bearings in pairs on each axle whenever possible, since if one has worn out already its counterpart often follows soon after.
Wheel bearing replacement cost depends on the vehicle's make and model but usually runs between $150-$400 per pair in labor to press out the old bearings and install new ones properly. Parts range from as little as $50 on economy cars to up to $250 for heavy-duty SUV wheel bearings.
Doing this repair yourself requires an experienced hand, a beefy arbor press, proper tools, and know-how. However, the cost savings of DIY bearing replacement make tackling this job worthwhile for capable mechanics. Just be sure you purchase the exact replacement bearing and races needed for your vehicle’s year, make, and model.
The Bottom Line
Don't ignore worn wheel bearings that make excessive noise or exhibit other symptoms of impending failure. Damaged bearings reduce braking ability, lead to uneven tire wear, and lower gas mileage, and can completely seize up if left unattended. Catching deteriorating bearings early makes the repairs faster, and cheaper and minimizes risks of getting stranded out on the highway if a bearing lets go entirely. Replace worn automotive wheel bearings promptly in pairs for best results.
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