The second mistake we should all avoid is adding too much, or not enough grease. Too much grease builds up pressure pushing the rolling elements through the fluid film and against the outer race. Increased friction and temperature dramatically shorten the bearing’s life. Not enough grease will have the same life-shortening effect.
How do we know when just the right amount of grease has been added? Ultrasound of course. Listen to the bearing and measure the drop in friction as the grease fills the bearing cavity. As the decibel level approaches normal baselines and stabilizes carefully slow the application of lubricant. Should the decibel level begin to increase slightly, STOP! The job is done.
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Lubrication, Ultrasound by Allan Rienstra - SDT Ultrasound Solutions