The following are facts every technician should know about bearing grease:
Lubricants aid in carrying away heat, protecting bearing surfaces from corrosion and reducing friction.
Overfilling a bearing with too much grease can cause excess churning of the grease during operation and high temperatures, resulting in overheating and excess grease purging* (leaking). Overheating occurs because the heat generated cannot dissipate correctly, continually building until damage occurs.
When a bearing overheats and pushes out the grease, the sealing lip can be damaged and “blown out” in the reverse direction.
When the grease amount is low, a grease starvation condition may be created, causing heat generation or excessive wear during operation.
Grease is a precise combination of oil, thickener and additives. Grease acts like a sponge to retain and release the oil. As a result of time and temperature conditions, the oil release properties can become depleted. When this occurs, the grease is worn-out.
Colored and UV dyes can be added to a grease as assembly aids or to facilitate inspections. The original color of a grease has little to do with its performance.
Automotive wheel bearing grease contains corrosion inhibitors and anti-wear and water-resistant additives, offering superior protection in challenging environments.
A softened sealing lip surface is the sign of a compatibility problem with the grease and seal. The wrong grease can cause a rubber seal to swell and disintegrate.
The fresh grease is smooth and buttery compared to the water-laden grease, which is milky white in appearance. As little as one percent water in grease can have a significant impact on bearing life.
About the Author
Andrew Markel
Editor, Brake & Front End Magazine
amarkel@babcox.com
Andrew Markel is a former technician and service writer and he brings this practical knowledge to the Brake & Front End team as editor.
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