The short version
- Six mechanisms account for almost every failure, and only one of them is a bad part.
- False brinelling damages bearings on vehicles that never move, which is why shipped cars arrive noisy.
- Electric vehicles have a failure mode combustion cars do not, caused by stray current.
- Each mechanism leaves a different mark, so the damage usually identifies its own cause.
Understanding what causes wheel bearing failure matters more than it sounds. The answer changes what you do next.
If the part was defective, fit another one. If something else destroyed it, fitting another one just restarts the clock.
The six mechanisms
| Mechanism | What it is | Mark it leaves |
|---|---|---|
| Contamination | Water or grit past the seal | Rust pitting, dull scratched races |
| True brinelling | Impact load through the elements | Dents at element spacing |
| False brinelling | Vibration with no rotation | Polished marks at element spacing |
| Fatigue spalling | Normal life running out | Flakes lifting from the raceway |
| Overheating | Preload, drag or dead grease | Blue or straw discoloration |
| Electrical discharge | Current passing through | Fine parallel fluting |
Only the fourth row is a bearing simply reaching the end of its design life. The rest are things done to it.
Contamination, the most common by far
Seals are the actual weak point on a modern hub, not the bearing.
Water gets past a tired seal, displaces the oil film, and lets the raceways corrode. Those pits act as stress raisers, and the surface starts flaking from them.
There is a pressure mechanism behind it too. A hub heats in use and cools when parked, so the trapped air expands and contracts. Cooling draws whatever is outside the seal inward.
That corner runs nearest the gutter, where standing water is deepest and spray is heaviest. Same seals, same bearing, far more water.
It is also why a car left outside through winters fails sooner than one covering the same miles in a dry garage.
True brinelling
Named after the hardness test that leaves a similar mark, and it is permanent.
When force passes through the rolling elements rather than around them, each element is driven into the raceway hard enough to dent it.
Two things do this. A heavy impact such as a pothole or a curb strike, and pressing a bearing during installation with the load crossing the balls.
The tell is diagnostic. The dents sit at exactly the rolling element spacing, evenly around the race, because that is where the elements were when the load arrived.
Avoiding it during fitting is the whole reason for the driver rules on the press tools page.
False brinelling, which happens with no impact at all
This one is badly under-discussed. It explains a category of complaints that otherwise makes no sense.
A stationary bearing under vibration has rolling elements that rock a fraction of a millimeter back and forth without ever rotating.
Rotation is what drags fresh oil into the contact. Without it the same tiny patch is worked over and over, the film is squeezed out, and the surfaces wear in place.
A vehicle carried on a truck or rail car spends days vibrating while its wheels never turn. So does one parked for months near a road or machinery.
The result is a hum from almost the first mile on a car with delivery mileage. Nothing was defective and nothing was fitted badly.
The marks sit at the same element spacing as true brinelling, but polished rather than dented. Long distance transport and long storage are the two usual histories.
Fatigue spalling, the honest end of life
The only mechanism here that represents a bearing simply wearing out.
Every pass of a rolling element puts the metal just below the surface through a stress cycle. Do that enough million times and a crack starts below and works upward.
When it reaches the surface a flake lifts out, leaving a pit. That pit then damages every element that passes over it, and the process accelerates.
This is the wheel bearing failure the rating life equation actually predicts. How fast you reach it depends overwhelmingly on load, as the lifespan page works through.
Overheating
Rarely a first cause and frequently the mechanism that finishes the job.
Grease degrades roughly twice as fast for every 15 degrees Celsius of extra heat, which the grease page quantifies. Once it breaks down, friction rises and produces more heat still.
Three things start that loop. An over-torqued axle nut crushing the races, a dragging caliper dumping heat into the hub, or a bearing already damaged another way.
The evidence is color in the steel. Straw and blue tints mean the surface was hot enough to change its temper, and that hardness does not come back.
Electrical discharge, the new one
A mechanism that barely mattered on combustion cars and matters increasingly now.
Electric drivetrains can produce stray currents looking for a path to ground. A wheel bearing sits between two conductive parts, separated by a thin insulating film of oil.
When the voltage across that film gets high enough it breaks down, and a tiny spark jumps. Each discharge melts a microscopic crater in the raceway.
Millions of those craters produce a regular washboard pattern called fluting. It generates a distinctive whine rather than the usual growl.
Manufacturers address it with conductive greases, insulated bearings and grounding rings. A home mechanic will not diagnose it, but the category is worth knowing about.
Why some models suffer more than others is on the bad models page.
What this means practically
Three conclusions worth acting on.
- A new bearing that fails fast is usually not defective. Installation damage and a mis-set axle nut cover most of those cases.
- Fix the cause, not just the bearing. A dragging caliper or a damaged knuckle bore will destroy the replacement too.
- Keep the old part. The damage identifies the mechanism, which matters for a warranty claim and for avoiding a repeat.
Correct fitting removes two of the six mechanisms outright. That is the largest return available for the effort, and getting the axle nut right removes a third.
Heat is the symptom that means stop rather than schedule, and reading hub temperature properly explains why you compare corners.
A single hard impact is its own case, and the pothole page explains why the noise only arrives months afterward.
Reading the old part afterward tells you which of these actually happened, and the failed bearing page shows how.
Common questions
What causes wheel bearing failure most often?
Contamination past a failed seal, usually water. It displaces the oil film and lets the raceways corrode, and the surface then flakes from those corrosion pits.
What causes wheel bearing failure in a new part?
Most often installation damage or an axle nut set wrong. Early wheel bearing failure on a new part is rarely the part itself.
Can a bearing be damaged without being driven?
Yes. False brinelling occurs when a stationary bearing vibrates, which happens during long distance transport and long static storage.
What does brinelling look like?
Evenly spaced marks around the raceway at exactly the rolling element spacing. Dented for true brinelling, polished for false brinelling.
What causes wheel bearing failure on an electric vehicle?
They can. Stray current passing through a bearing produces tiny discharges that erode the raceway into a fluted pattern, which sounds like a whine rather than a growl.
Does a dragging brake damage the bearing?
Yes, by heat. It cooks the grease, and degraded grease raises friction, which produces more heat in a loop that only goes one way.
Should I keep the old bearing?
Yes, at least until the job is settled. The damage pattern identifies the cause, which matters if you are making a claim or trying to avoid a repeat.