In the industrial world, a small part failing can have a huge impact on operations. For example, one failed bearing can snowball into hours of lost production and missed delivery deadlines.
The worst part? Most bearing failures aren’t freak accidents, they’re entirely predictable. But they often go unnoticed until it’s too late.
Whether you’re running a line in a food plant or managing heavy assets in steel, bearings are some of the most stressed (and least forgiving) components. And when they go down, so does everything around them.
But with a little practice, you can spot the warning signs and take action before that happens.
In this guide, we’re breaking down bearing failures from the ground up: what they are, what they look like as they progress, and how to stop their causes at the source.
Let’s start with the basics: what exactly qualifies as a bearing failure?
What Is A Bearing Failure?
A bearing failure happens when a bearing can no longer perform its intended function: supporting rotating motion while minimizing friction.
It’s not always a dramatic crash, though. In most cases, the failure builds up quietly, layer by layer, until it disrupts the entire system.
Technically speaking, a bearing is considered “failed” when it no longer meets its expected life or performance threshold, and this can happen from everyday wear and tear, misalignment, and a few other stressors.
Why Bearing Failures Matter
When a bearing fails, it stops spinning, which can translate to:
- Sudden equipment breakdowns
- Unplanned outages
- Delayed production runs
- Costly part replacements
What makes bearing failures especially frustrating is that they often stem from small, preventable issues: a missed lubrication schedule here, an improper installation there, etc.
99% of the time, bearing failures aren’t mechanical surprises; they’re the consequences of a lack of oversight.
Understanding what failure looks like and what causes it is the first step toward building a more proactive maintenance strategy.
So, let’s talk about how these failures happen over time and how to catch them early.
The 4 Stages Of Bearing Failure You Need To Know
Bearings don’t go from “healthy” to “destroyed” overnight. They break down in stages, and each stage leaves behind a clear signature.
If you know what to look for, you can spot trouble before it becomes a problem.
Stage 1
At this stage, the bearing is technically still in operation. There are no performance issues on the surface. But, damage is already starting to form at the microscopic level.
Small pits are developing in the raceways as rolling elements impact localized defects.
These show up as high-frequency signals, typically in the 20 kHz to 60 kHz range, which means traditional monitoring tools likely won’t pick them up.
This is your earliest window for action. If you’re using ultrasonic sensors or advanced condition monitoring, you can detect these shifts before they escalate.
Stage 2
As those microscopic pits grow, the damage starts to accumulate, and the bearing’s components start vibrating at their natural frequencies, usually between 500 Hz and 2,000 Hz.
This is the warning stage. For critical assets, it’s time to plan maintenance. You’re still early enough to avoid a line shutdown, but the clock’s ticking.
Stage 3
In Stage 3, the subtle damage becomes visible. Defect frequencies are strong, harmonics are easy to spot in the spectrum, and if you remove the bearing, you'll see clear wear on the raceways.
At this point, you’re dealing with progressive failure.
Non-critical assets might still run for a while, but critical ones need replacement ASAP. The risk of secondary damage is rising.
Stage 4
This is the point where the bearing has reached its end-of-life The bearing is breaking down across the board, and if you look at vibration data, you’ll see chaotic, broadband pattern.
Ironically, this stage might not show the highest amplitudes. Some systems actually quiet down slightly right before complete failure.
But don’t let that fool you. If you haven’t scheduled the replacement already, you're officially behind.
Symptoms Of Bearing Failure
Spotting a bearing failure before it hits full breakdown mode separates reactive teams from proactive ones. The key is knowing what symptoms to watch for, and not waiting to act on them.
Here are the most common red flags that a bearing is in trouble:
Unusual Noise
One of the first signs that something's wrong is a change in sound. Grinding, squealing, or knocking noises often mean the rolling elements are no longer gliding smoothly. By the time it’s audible, you’re already past Stage 1.
Increased Vibration
Rising vibration levels,especially in the bearing’s frequency bands, can signal anything from misalignment to spalling. It’s often the earliest measurable symptom, especially when it’s detected with condition monitoring tools.
Elevated Temperature
A failing bearing generates excess friction. This shows up as heat, often in combination with poor lubrication or overloading. Watch for temperature spikes that don’t correlate with workload changes.
Lubricant Issues
Dark, dirty, or metallic-filled grease is never a good sign. Contamination and lubricant breakdown go hand-in-hand with bearing degradation. If the lube looks off, chances are the bearing is too.
Visible Damage
Once you start seeing discoloration, scoring, or wear marks on the bearing housing or raceways, you’ve got solid proof.
Equipment Underperformance
When a bearing starts to go, overall equipment efficiency often dips. It might be subtle, but it’s always measurable.
13 Most Common Reasons Why Bearings Fail
In most cases, when a bearing fails, it’s not because of one catastrophic event. It's because of something small that was overlooked.
In fact, studies show that almost 80% of bearing failures trace back to one simple root cause: improper lubrication.
The rest come down to a mix of mechanical stress and bad handling practices.
Here are the 13 most common reasons bearings fail, and what you can do to avoid them.
1. Improper Lubrication
If there's one thing that tops every bearing failure chart, it’s lubrication. Bearings rely on a thin film of lubricant to reduce friction between moving parts. When that film breaks down, metal grinds on meta, building heat until the component fails.
These are the three main lubrication mistakes maintenance teams make:
- Under-lubrication: Not enough grease creates metal contact and overheating.
- Over-lubrication: Too much grease creates pressure, increases friction, and can cause the seal to fail.
- Wrong lubricant: Using a grease with the wrong viscosity or additives for your bearing type and load conditions leads to ineffective protection.
What to look for:
- Bluish or dark discoloration on the bearing surface
- Burnt grease smell
- Polished raceways or cage damage from excess friction
How to prevent it:
Stick to manufacturer specs, monitor relubrication intervals, and avoid "topping off" without cleaning. For your most critical assets, automated lubrication systems or real-time lube monitoring can help eliminate any guesswork here.
2. Cage Damage
The cage (or retainer) keeps the rolling elements evenly spaced and aligned. It might not seem like a critical component, but when it fails, the entire bearing becomes unstable.
What causes cage damage?
- Excessive vibration during idle or storage
- High-speed operation beyond design specs
- Inadequate lubrication, leading to increased friction and wear
- Contamination, which can wedge debris between the cage and rollers
- Improper installation that puts stress on the cage structure
Once the cage breaks, the rolling elements start to skid or bunch together, increasing the load on specific contact points.
That’s usually a quick path to total failure.
What to look for:
- Broken or warped cage segments
- Irregular movement of rolling elements
- Audible rattling or chattering during operation
How to prevent it:
Use soft starts to reduce shock loads and stay within the bearing’s speed limits. If possible, avoid running equipment with frequent start-stop cycles.
Don’t forget to store bearings properly as well. Too much vibration during storage can damage the cage before it’s ever put into use.
3. Contamination and Corrosion
Contamination and corrosion are silent killers. Even microscopic particles or moisture can initiate a chain reaction leading to premature failure.
What causes contamination and corrosion?
- Ingress of solid particles: Dust, dirt, or metal shavings entering the bearing housing
- Moisture intrusion: Water or humidity creates rust and degradation
- Chemical exposure: Harsh chemicals attacking bearing materials or lubricants
- Ineffective seals: This allows external contaminants to penetrate the bearing environment
Once contaminants enter, they disrupt the lubricant film and lead to corrosion eventually.
What to look for:
- Pitting or rust marks on raceways and rolling elements.
- Discoloration or degradation of lubricant.
- Unusual noise or vibration during operation.
How to prevent it:
Start by making sure your sealing system blocks contaminants from entering the system.
Maintaining a clean environment is also critical to avoid introducing debris or moisture.
Lastly, seals and lubricants should be inspected regularly and replaced as needed.
4. Electric Arcing
Electric arcing — also known as electric discharge or EDM (Electrical Discharge Machining) — happens when stray currents pass through the bearing. It's more common than many teams realize, especially in motors with variable frequency drives (VFDs).
What causes electric arcing?
- Improperly grounded motors
- Shaft voltage buildup due to VFDs
- Lack of insulation between motor and bearing elements
When currents jump across the bearing's rolling elements, it creates localized high-temperature spots.
These micro-weld and melt the metal on contact, forming pits on the raceways. Over time, this leads to a frosted or fluted surface finish, a textbook sign of electric damage.
What to look for:
- Fluting or ridged patterns on the raceways
- Premature lubricant breakdown
- Increased noise and vibration in motors with VFDs
How to prevent it:
Use insulated bearings or grounding brushes for motors running on VFDs, and conduct shaft voltage tests during commissioning.
You’ll also want to make sure electrical equipment is properly grounded and bonded.
5. Poor Fitting
Whether the bearing is too tight or too loose on the shaft or housing, both scenarios create stress conditions that the component wasn’t designed to handle.
What causes poor fitting?
- Shaft or housing tolerances that don’t match bearing specs
- Improper mounting tools or techniques
- Thermal expansion that’s not accounted for during installation
- Using a hammer or press without proper alignment
An overly tight fit reduces internal clearance, leading to excessive preload, increased friction, and overheating.
A loose fit allows the bearing to move (creep), creating wear on the mounting surfaces.
What to look for:
- Fretting corrosion on the shaft or housing
- Excessive vibration and noise after a recent bearing replacement
- Cracked or deformed bearing rings
How to prevent it:
Always follow the OEM’s guidelines for fit tolerances.
And before installation, confirm that the shaft and housing dimensions are precise. Use specialized tools to mount components correctly, so every bearing has a uniform and controlled fit without damaging internal structures.
And whatever you do, leave brute force out of the equation. Improvising during installation increases the risk of misalignment and brings unnecessary stress that can lead to cracking or deformation down the line.
6. Fatigue
Also mentioned as “spalling”, fatigue is the gradual breakdown of bearing material under repeated stress. While it’s considered a natural wear-out mode, it shows up far earlier than it should when loads exceed design limits or bearings aren’t lubricated properly.
What causes fatigue?
- Repeated cyclic loads beyond bearing capacity
- Inadequate lubrication that increases contact stress
- Micro-cracks from surface defects or previous damage
- Excessive temperature variations that alter material properties
What to look for:
- Pitting or flaking on raceways
- Increased vibration and noise
- Decreased bearing life vs. expected run hours
How to prevent it:
First of all, make sure to match every bearing size and type to your actual load conditions.
Along with maintaining consistent lubrication, you should also try to avoid shock loads during startup and shutdown. And for high-load applications, use bearings with fatigue-resistant coatings.
7. Brinelling
Brinelling is the formation of permanent indentations on the bearing raceways. It’s one of the most visible (and most misunderstood) forms of bearing damage.
There are two types: true brinelling and false brinelling. Both look similar, but they come from different causes.
What causes brinelling?
- True brinelling: Happens when static loads exceed the elastic limit of the bearing material. This often happens during improper installation (like hammering a bearing onto a shaft) or from shock loading while the equipment is stationary.
- False brinelling: Caused by vibration or oscillation during idle periods. The bearing isn’t rotating, but micro-movements cause wear marks that mimic true brinelling.
What to look for:
- Dent marks spaced evenly around the raceway (matching the roller or ball spacing)
- Increased vibration and noise during rotation
- Early-stage fatigue and lubricant failure near the dents
How to prevent it:
Never use a hammer for installation, and ensure proper support and alignment. In storage, avoid high-vibration areas or rotate shafts regularly. For vibration-heavy setups, use damping mounts or apply preload.
It’s all about minimizing impact and micro-movements before they cause permanent damage.
8. Misalignment
Misalignment happens when the shaft and bearing housing aren’t properly aligned.
Even a slight angular offset can throw off the load distribution and put uneven stress on bearing components.
What causes misalignment?
- Bent shafts or improperly machined housings
- Incorrect installation of mounting hardware
- Shaft shoulders or locking nuts that aren’t square
- Thermal expansion that shifts component positions during operation
Misalignment forces the rolling elements to skew or tilt within the races. This leads to edge loading and accelerated wear on one side of the bearing.
What to look for:
- Uneven wear patterns across the raceways
- Vibration signatures with harmonics related to misalignment
- Elevated temperatures in localized areas of the bearing
How to prevent it:
Being precise during setup makes for a longer bearing life. To do this, use laser alignment tools or dial indicators, inspect for burrs or defects on shafts and housings, and always re-check alignment after thermal cycles or rebuilds.
If perfect alignment isn’t realistic, go with self-aligning bearings.
9. Path Patterns
Every wear path on a bearing tells a story. By analyzing the contact pattern left on the raceways, you can often reverse-engineer the root cause of failure, even if the bearing is already out of service.
What causes abnormal path patterns?
- Misalignment or shaft deflection
- Poor load distribution due to incorrect fit
- Overloading or vibration during operation
- Contamination or improper lubrication shifting the load zone
A clean, centered wear path means the bearing operated under ideal conditions. Deviations—like oval-shaped or offset paths—signal that something in the system was off.
What to look for:
- Patterns shifted toward one side of the raceway
- Irregular or discontinuous contact lines
- Pattern shapes that don’t match normal rolling behavior
How to prevent it:
Always inspect and document wear marks during teardown. Properly align and balance rotating parts, and follow fit and mounting specs to the letter.
You can also compare real loads to the bearing’s design limits. This level of path pattern analysis helps catch what others miss and stops repeat failures before they start.
10. Seal Selection & Maintenance
Seals are the first and often only line of defense against contamination, and when they fail, your bearings are exposed to everything the environment throws at them.
What causes seal-related failures?
- Choosing the wrong seal type for the application (e.g., using standard seals in wet or dusty environments)
- Damaging seals during installation or cleaning
- Excess grease purging through seals, weakening or dislodging them
- Skipping seal inspections during routine maintenance
A compromised seal allows contaminants to enter the bearing housing. That not only ruins the lubricant but also accelerates surface wear.
What to look for:
- Grease leaking past the seal
- Physical damage like cracks or warping
- Increased contamination inside the bearing housing
How to prevent it:
A bearing’s reliability depends on its seal. Choose seals that match the environment you’re working in.
In abrasive areas, add shields or guards. Avoid over-lubricating, which can blow seals out of position.
Lastly, don’t skip inspections.
11. Overload
Bearings are designed to handle a specific load range. Exceed that, and you're on the fast track to failure.
Overloading puts extreme stress on the rolling elements and raceways, creating plastic deformation and early spalling.
What causes overload?
- Unexpected process surges or shock loads
- Incorrect bearing selection for the applied force
- Structural misalignment transferring excess load to the bearing
- Shaft deflection or uneven load distribution
Sometimes, the bearing keeps running, just not for long. It heats up and starts generating abnormal vibration as surfaces break down.
What to look for:
- Flattened or deformed rolling elements
- Crushed or flaked material on raceways
- Heat discoloration and rapid lubricant degradation
How to prevent it:
Match bearing specs to real application loads, not just theoretical ones. Monitor load conditions during operation, especially in variable processes.
For shock or impact scenarios, add damping or isolation. And, always apply dynamic and static ratings correctly.
12. Improper Handling & Storage
Bearings are precision components, and they don’t leave much room for carelessness. Dropping a box or handling them with dirty gloves can all introduce damage before they even reach your equipment.
What causes failure from poor handling or storage?
- Physical impacts during transport or installation
- Exposure to moisture
- Dust or debris contaminating the bearing before mounting
- Long-term storage without rotation (leading to false brinelling)
Improper storage often causes corrosion or vibration wear, while improper handling can dent raceways and create alignment issues.
What to look for:
- Rust marks or moisture residue on the bearing surface
- Small dents or flat spots on rolling elements
- Signs of dirt or damage on inner packaging
How to prevent it:
Bearings demand clean, dry, and vibration-free storage. Keep them sealed in their original packaging and rotate periodically to avoid false brinelling.
You’ll also need to train teams to handle them right: no bare hands, no drops.
13. Inadequate Internal Clearance
Internal clearance represents the total distance one bearing ring can move relative to the other.
It may sound minor, but get it wrong, and you’ll either choke the bearing or let it run loose.
What causes clearance issues?
- Incorrect bearing selection (clearance class doesn’t match the application)
- Excessive interference fits during mounting that reduce internal space
- Thermal expansion of the shaft or housing without compensation
- Improper preload settings in assemblies
If the clearance is too tight, there’s not enough room for thermal growth or lubricant film.
Too loose, and the bearing loses stability, increasing vibration and load imbalance.
What to look for:
- Overheating shortly after start-up
- Excess axial or radial play
- Accelerated wear, especially near the edges of raceways
How to prevent it:
Always select the right clearance class (C3, C4, etc.) for your application. Next, don’t forget to factor in thermal expansion during design and mounting, and follow fit and preload guidelines precisely.
If you find that temperatures keep spiking in bearing zones, reassess your setup.
Predictive Maintenance For Bearing Failures
The best way to deal with a bearing failure is to prevent it from happening in the first place. Predictive maintenance makes that possible.
Instead of relying on run-to-failure or rigid preventive schedules, predictive strategies use real-time data to identify early warning signs.
Within predictive maintenance, vibration analysis is one of the most effective methods for detecting early-stage bearing defects. We’ve broken down how this works in detail in our full article on bearing vibration analysis.
With the right tools in place, your team can act before that stress turns into downtime.
And catching those signals means choosing the right monitoring approach. That’s where condition-based strategies come into play.
How Tractian's Condition Monitoring Solution Can Help Prevent Bearing Failures
Condition monitoring is the new baseline for data-driven maintenance.
By continuously tracking the health of your equipment, you get real-time visibility into how each component is performing. Temperature, vibration, and more are all captured without shutting machines down or disrupting operations.
No more waiting for symptoms. Instead, you spot them while your assets are still running.
And it’s not just about avoiding breakdowns. It’s about making better calls with fewer resources, protecting uptime, and giving your team the time and data to focus on what really matters.
