Tuesday, July 16, 2024

Wheel bearing failure


> > Wheel bearing failure

According to studies conducted by bearing manufacturer SKF, 90% of all OE bearings outlast the life of the vehicle. However, 0.5% of those OE bearings fail because due to damage or wear caused by outside forces. 0.5% translates into 50,000,000 bearings per year.

Wheel bearing failure breakdown

• 1/3 fail due to fatigue• 1/3 fail due to lubrication problems (wrong lubricant, wrong quantity, wrong lubrication interval)• 1/6 fail due to contamination due to water ingress caused by failed seals• 1/6 fail for other reasons like impacts from potholes or driving on rough roads, overloading, unbalanced tires, accident impacts (curb kisses), radical car modification, and improper bearing installation/replacement procedure.

Lubrication problems are a major cause of bearing failure

Whether the bearings are tapered roller, cartridge or hub style, they’re all protected against water and debris ingress by grease seals. Older tapered roller bearings used non-integrated seals that install into the rotor. Newer bearings have integrated seals in the cartridge or hub.

However, no matter the type of seal, all seals can fail and allow water and debris into the bearing and that contaminates the grease causing it to fail. Once the grease fails, the bearing starts to rust and wear.

What causes wheel bearing grease failure?

• Not replacing grease seals when repacking tapered bearings• Water ingress caused by driving through deep puddles• Overheating caused by too much grease (more is not better) or using the wrong grease

Water ingress, grease failure and rust

Wheel bearing spalling damage and how it progresses
Wear, pitting and bruising

Any hard particles traveling with the lubricant can cause a “bruise” or dent on the  bearing or race surface. The dents can also be caused by impacts (potholes and rough road surface). The raised metal around the dent acts as surface-stress risers that cause spalling. Spalling is the pitting or flaking away of bearing material on the races and rolling elements.

Brinell damage

There are two type of Brinell damage: true brinelling and false brinelling.

True brinelling is common in automotive applications

True brinelling is caused when the load on the bearing is greater than the elastic limit of the ring or bearing material. It can also be caused by shock or impact. It appears as regularly-spaced indentations in the bearing raceway and rolling elements, and an increase in vibration.

False Brinelling

False brinelling is caused by vibrations acting on the bearing while the bearing is in a non-rotating state. The vibration causes the bearing to wear against the race. This rarely happens in automotive bearings and is more common in industrial machines with strong vibrations.

Electrical deterioration in wheel bearings

Electricity will always seek the path of least resistance to ground. In a properly wired vehicle, that path will always be through the grounding cables connected to the engine, firewall and body and then to the negative post on the battery. However, if the engine grounds are missing, the electrical path from the engine to the body and then to the battery will be through the wheel bearings (engine/transmission to axle, to wheel bearing, to steering knuckle/strut, to strut mount, to body, to battery negative battery terminal.

This electrical patch can deteriorate the grease in the bearing, causing the bearing to fail.

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