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Pulley bearings. When it spins freely. Why exactly is this bad?

Listen to the bad pulley. What has happened inside?
It spins freely, no resistance. Unlike when new.
But, why isn’t this a good thing? (Less resistance…)

If you spin any kind of sealed bearing and the bearing makes any kind of noise it means the factory lubricant is gone. The noise is caused from the rollers in the dry bearing spinning on the races in the bearing.

Tester

It’s not a case of less resistance.

The pulley may be turning at an acceptable rate today, even though its bearings are now dry.
However, at an unknown point (tomorrow, or next week, or in the middle of your next highway trip), the bearings in that pulley will seize, and at that point, the serpentine belt will shred/self-destruct.

This is something that you want to avoid–unless you relish the idea of needing a tow from the shoulder of a high-speed expressway, or a dodgy neighborhood, or some other dangerous area.

See 4:00 in the video.
Ok, so this means the lube is gone, and eventually it WILL seize.
Thanks!

Good info.

Good ball bearings run silently…Polished steel against polished steel, lubricated…Smooth as silk…

First the seal goes…Then the lubricant goes…Then the bearing wears and gets rough…The balls start to jam and slide…The bearing fails…The pulley stops turning or fly’s off…

…and that’s when you wish you had your video camera rolling.

While in operation the pressure and speed would make for a much different situation. If manually turning such a device indicates that it is free wheeling the balls are not rolling indicating that they are flat spotted and useless.