Wheel bearings are a crucial component in automobiles that allow the wheels to spin freely while supporting the weight of the vehicle. Over time, these bearings can wear down and fail, leading to a variety of problems. Understanding the causes of bad wheel bearings can help drivers prevent and address these issues.
What are wheel bearings?
Wheel bearings are sets of steel balls or tapered rollers contained in a metal ring called a race. They are located inside the wheel hubs, which are the mounting components that hold the wheels onto the axles. Most cars have sealed wheel bearings that are lubricated for life and do not require maintenance.
The wheel bearings allow the wheels to spin with minimal friction while supporting the weight of the vehicle. There are a few different types of wheel bearings:
- Ball bearings – Use steel balls between an inner and outer race to reduce friction
- Tapered roller bearings – Use cone-shaped rollers between races for heavy load capacity
- Cylindrical roller bearings – Use cylinder-shaped rollers between races, often found on non-driven wheels
No matter the exact type, wheel bearings are constantly rotating at high speeds whenever the vehicle is moving. This puts them under a lot of stress and wears them down over time.
What causes wheel bearings to fail?
There are several potential causes of wheel bearing failure, including:
Normal wear and tear
Wheel bearings are designed to last tens of thousands of miles under normal driving conditions. However, the constant rotation under heavy loads will eventually wear them down, causing imperfections in the metal that can lead to failure. Higher mileage vehicles may experience bearing wear out due to age alone.
Improper lubrication
Most modern wheel bearings are lubricated for life and do not require routine maintenance. However, if the factory lubricant has leaked or dried out, the bearings can overheat and fail prematurely. Lack of lubrication leads to excessive friction and wear.
Extreme driving conditions
Aggressive driving over rough terrain or at high speeds can stress the wheel bearings beyond their design capacity. Off-road use, potholes, and high-performance driving can all cause early bearing wear. Excessive cornering forces also burden the bearings.
Improper wheel installation
If a wheel is installed incorrectly after a tire change or brake service, the wheel bearing can be knocked out of proper alignment. This leads to uneven contact within the bearing and accelerated wear. Proper torque specifications must be followed.
Excessive vehicle load
Overloading a vehicle places more weight on the bearings than they are designed to handle. The constant heavy load causes premature wear. This is most common with trucks and tow vehicles.
Bent axle shaft
If an axle shaft gets bent or damaged in a collision or from striking objects on the road, it can place uneven stress on the wheel bearings. This side load can quickly cause bearing wear and tear.
Rusted components
Exposure to water, road salt, and other contaminants can cause the bearing components or races to rust. This leads to pitting, binding, and accelerated deterioration of the bearing. Seals should be intact to prevent contamination.
Symptoms of failing wheel bearings
Drivers will notice a few warning signs indicating wheel bearing damage and impending failure:
Noise
As bearings wear, they can begin to make various noises when driving including growling, rumbling, roaring, and grinding. These noises get louder as the bearings degrade further.
Vibration
Excessive wheel bearing play allows the wheel hub to wobble slightly while rotating. This imbalance causes vibrations that can be felt in the steering wheel, seat, or floorboards.
Loose steering
Worn bearings can allow too much clearance between the wheel hub and steering components. This makes the steering feel loose or vague.
Uneven tread wear
Bad bearings alter the wheel alignment leading to uneven tire tread wear. The tires will show excessive shoulder or center wear on the affected side.
Fluid leakage
Once bearings are severely damaged, their grease seals fail allowing lubricant to leak out. Oil staining around the wheel hub indicates total bearing breakdown.
Diagnosing bad wheel bearings
Driver complaints of noise, vibration, or loose steering should lead to inspection of the wheel bearings. Some diagnostic steps include:
- Check for fluid leaks near the wheel hubs
- Inspect tires for uneven tread wear
- Rock and wiggle each tire to feel for excessive play
- Listen closely for any growling or rumbling noises
- Test drive to verify issues during operation
- Measure ride height to check for suspension collapse
Wheel bearings that show signs of wear should be further evaluated using a dial indicator or Hubmatch system. These measure the precise axial and radial play quantitatively. Any measurement over the manufacturer’s tolerance requires replacement of the bearing.
Repairing and replacing bad wheel bearings
Damaged wheel bearings must be replaced immediately to avoid catastrophic failure and a wheel separating from the vehicle while driving. Here are some repair considerations:
Bearing configuration
Most modern vehicles use sealed, self-contained hub units that do not allow just the bearing itself to be replaced. The entire hub must be serviced as an assembly. Older vehicles have adjustablewheel bearings that can be overhauled.
Other worn parts
When replacing wheel bearings, technicians should also inspect related components like axle seals, locking hubs, and CV joints. If damaged, these parts should be replaced at the same time.
Adjustment and torque
Wheel hub units are pre-adjusted but older style bearings require proper adjustment of the end play. All fasteners must be torqued to OEM specifications after installation to ensure proper seating.
Post-service testing
After new wheel bearings are installed, the wheel should be rechecked for play and proper rolling torque should be verified on both sides. A road test will confirm normal vibration-free operation.
Preventing wheel bearing damage
While wear is inevitable, drivers can help maximize wheel bearing life and avoid premature failure with proper maintenance:
- Inspect seals periodically and replace cracked or leaking ones
- Clean hub caps and check for excessive grease leakage
- Torque wheels properly after tire rotations or brake service
- Avoid potholes and curbs that can bend suspension components
- Keep loads balanced and within axle ratings
Catching bearing issues early and avoiding contaminated or overheated bearings will help achieve their maximum service interval. But no matter how well maintained, wheel bearings will eventually require replacement.
Conclusion
Wheel bearings endure punishing amounts of stress over thousands of miles to provide smooth and safe operation. While robustly engineered, bearings will inevitably wear out due to friction and contamination. Allowing bearing damage to persist uncorrected can lead to catastrophic failures.
Being aware of the warning signs of bad wheel bearings allows prompt diagnosis and repair. Technicians must follow proper procedures and use quality components when replacing worn bearings. With routine inspection and careful driving habits, drivers can maximize the lifespan of these critical components.