The short version
- The old bearing tells you why it failed, and that decides whether the new one will too.
- Where the damage sits matters more than how much of it there is.
- Evenly spaced marks mean vibration. One concentrated patch means an impact.
- Blue or straw discoloration is heat, and heat always has a separate cause worth finding.
Reading a failed wheel bearing takes about five minutes and it is the step almost everybody skips, because the part is already in the bin.
A failed wheel bearing is worth five minutes for one reason. If something other than age killed it, that something is still present.
What to look at, in order
A failed wheel bearing has four surfaces worth reading, and each answers a different question.
| Surface | What it tells you |
|---|---|
| Outer raceway | Load direction and the failure pattern |
| Inner raceway | Whether it spun on the hub |
| Rolling elements | Whether debris got in |
| Seal and its lip | How the contamination arrived |
The seal is the one most often ignored and the one that most often carries the answer.
The patterns and what causes them
Evenly spaced dull patches around the raceway, at the rolling element spacing. That is false brinelling, from vibration while stationary. The sitting page covers it.
One concentrated dented area. True brinelling from a single impact, which points at a pothole or curb strike. That is on the impact page.
Flaking and pitting spreading from a patch. Spalling, the normal end of fatigue life, and the least alarming finding.
Fine matte etching over a broad area. Corrosion from water ingress, which sends you to the seal.
Scoring and embedded particles. Contamination, meaning grit got past a seal or was present at assembly.
Blue, brown or straw coloring. Heat. That is never the root cause, only evidence of one.
A bearing that simply fatigued out, with a clean seal and no discoloration, reached the end of its design life.
Everything else on that list means a cause that will still be there when the new bearing goes in.
Where the damage sits
This is the part that gets overlooked, and it is more informative than the damage type.
A bearing does not carry load evenly around its circumference. The load zone is a band, and normal wear appears there.
Marks in the unloaded region cannot have come from ordinary running loads, because that area never carries much.
It points at an impact, at vibration while stationary, or at the bearing having been fitted with force through the wrong race.
Fitting damage in particular shows up as marks the running loads could not have made. What causes it is on the pressed-in procedure page.
Reading the seal
Four things to check, and any one of them explains a contaminated bearing.
- Is the lip torn, split or missing sections? A physical breach with an obvious consequence.
- Is the rubber hard rather than pliable? Age or heat, and it will not have been following the surface.
- Is the running surface corroded or scored? Then the seal was riding on something rough.
- Is the garter spring still present and tensioned? A lost or relaxed spring means no sealing force.
What each finding means for the replacement is on the seals page.
The grease is half the story
If any grease is left, it carries as much information as the metal does.
Pale and mayonnaise colored is water emulsion. Dark and gritty is contamination. Dry, hard and crusted is heat.
The full reading is on the used grease page, and it pairs with what the raceway shows.
What each finding changes
| Finding | What to do differently |
|---|---|
| Spalling only, clean seal | Nothing, it lived its life |
| Corrosion, breached seal | Find the water route, check hub and shield |
| One impact dent | Check the wheel and alignment for related damage |
| Even spaced marks | Storage or transport, not a fitting problem |
| Heat discoloration | Check brake drag and adjustment before refitting |
| Spun inner race | Check the hub or shaft is not now undersize |
| Damage outside the load zone | Review how it was fitted |
The heat row is the one most worth acting on. A dragging caliper that cooked one bearing will cook the next one too, and the hot hub page covers finding it.
If it is a sealed unit
An honest limitation, since most modern hubs cannot be opened without destroying them.
You can still learn a lot from the outside. Check both seals, look for rust streaks or grease escaping, feel for roughness, and look for heat coloring on the flange.
A hub that is visibly wet with grease has a breached seal, which is a diagnosis in itself.
If the replacement fails early, having the original to compare against makes the pattern obvious.
Two bearings failing the same way is a cause. Two failing differently is bad luck.
Why none of that damage can be reconditioned is on the remanufactured page.
Why hardened bearing steel flakes rather than wearing smooth is on the materials page.
Common questions
Why bother reading a failed wheel bearing?
Because if something other than age killed it, that cause is still present and will shorten the new one too.
Reading a failed wheel bearing: what does spalling look like?
Flaking and pitting spreading outward from a patch. It is the normal end of fatigue life and the least worrying finding.
What do evenly spaced marks mean?
False brinelling from vibration while stationary, usually storage or transport rather than anything you did while driving.
What does blue or straw coloring mean?
Heat, which is never a root cause on its own. Check for brake drag or overtightening before fitting the replacement.
Why does the location of damage matter?
Because normal running loads only mark the load zone. Damage outside it points at an impact, at stationary vibration, or at fitting force through the wrong race.
What should I check on the seal?
Whether the lip is torn, whether the rubber has hardened, whether the running surface is corroded, and whether the garter spring is still tensioned.
Reading a failed wheel bearing that is a sealed hub?
Partly. Check both seals for breaches, look for escaping grease or rust streaks, feel for roughness, and look for heat coloring on the flange.