The sound of ball bearings seizing up

There’s a characteristic sound of bearings seizing up, and I first came across this with car wheel-bearings – they screech for weeks before going, but car sounds are hard to localise. Feeling the massive heft to the right in the fast lane of the A12 as the driver’s side wheel-bearing collapses and jams means I know that this sound means a bearing on the way out, even if here it is only on a neighbour’s Flymo 🙂

a person that started in to carry a cat home by the tail was getting knowledge that was always going to be useful to him, and warn’t ever going to grow dim or doubtful.

Mark Twain, Tom Sawyer Abroad

Spectrogram of the mode-shift around 20s in

What the sound is is the end of the bearing precessing around the axis in the gap between the rotating shaft and the bearing housing. Once this had grease in it, but when it runs dry the shaft rattles about, and the mode-shift is probably another little bit of the housing being taken out.

When this starts to happen to a bearing, the pitch of the screaming starts off high, as there is little play and the gap is small. Grease the sucker at this point and you can have years of future service, I heard this on our tractor gearbox, greased the grease nipple, sound gone and years of service had.

As the wear continues, the pitch falls, in this case its about 2kHz. It’s a lost cause, there’s no grease in the world thick enough to stave off the deterioration and the bearing will eventually collapse and seizes…

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