Brinelling
A form of mechanical wear characterized by permanent indentations in a bearing race from overload or static impact.
Brinelling is a type of mechanical wear that occurs in rolling-element bearings, such as wheel bearings, when the bearing is subjected to excessive loads or static impacts. The term is named after the Brinell hardness test, as the resulting damage resembles the spherical indentations left by a hardness tester. It represents a permanent plastic deformation of the bearing races rather than wear from normal operation.
There are two main types: true brinelling and false brinelling. True brinelling is caused by a singular heavy impact or overload while the bearing is stationary, pressing the balls or rollers directly into the race. False brinelling is caused by micro-oscillations and vibrations while the bearing is stationary under load, which wear away the lubrication and cause localized fretting wear that mimics impact indentations.
Symptoms of brinelling in a wheel bearing include a low-pitched humming or growling noise that changes pitch with vehicle speed and steering direction. Once brinelling has occurred, the bearing cannot be repaired and must be replaced. Mechanics diagnose bearing damage using a chassis ear stethoscope or by spinning the wheel hub assembly by hand to feel for roughness.