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Ball bearing size and quantity query

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Ball bearing size and quantity query

Old 03-21-16, 01:34 PM
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Ball bearing size and quantity query

Hi Guys,

I recently got a Giant Sedona 2012 but found some play in the rear wheel bearings.
I took it apart and I found that one side looked good but the drive side contained 9 x 1/4 in balls with a large gap. Inside the axle there was a tenth ball which I thought must fit in the gap. No way, it was just slightly too big to fit.
I took the wheel to a bike shop and they just refitted the shaft with the original 9 bearings which they said was OK.
My question is should there be any gap in the bearings (almost a 1/4 inch in total) or should there have been maybe 10 or 11 smaller bearings which would fit snuggly?
Also not sure if it is a Giant back wheel as it is heavier duty than the front and is not marked "Giant"

Trying to learn fast
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Old 03-21-16, 01:48 PM
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9 x 1/4-inch ball bearings per side sounds right for a normal rear hub. It's not supposed to be a tight fit so a gap is normal.

Also, Sheldon Brown's site is an excellent resource of knowledge for people just learning or anybody else for that matter. If you like, you can start reading from the beginner's page.

Last edited by J.C. Koto; 03-21-16 at 01:51 PM.
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Old 03-21-16, 02:10 PM
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A gap, typically less than what one ball would fit is both normal, and necessary to the function of a ball bearing.

A properly built, and/or adjusted will have all balls in contact and under a slight load at all times. The overall bearing load from the weight on the axle is added to the load at the bottom, but unless the bearing is overloaded, doesn't change the other loads.

As such the force on the balls is purely radial, and happenstance and the lube's hydraulic pressure will cause the balls to spread themselves out somewhat equally. If the balls were overcrowded and made contact with each other it would prevent that natural spreading and cause friction as the adjacent ball surfaces rubbed past each other.

By the same token, a no gap design would make bearing construction nearly impossible, because ball to ball contact would prevent the radial contact necessary. By the same token, if the gap is too large the load might force the axle down slightly between the lowest balls, spreading them apart, and increasing both wear and vibration.

As for your 10th ball, odds are that it came from the other side, though on some hubs there's a recess behind the cup where an extra ball that was dropped during assembly could hide harmlessly until discovered by the first person to look.
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Old 03-21-16, 02:32 PM
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I just picked up a used Specialized Hardrock bike to refurbish and have the rear hub apart. There are 18 1/4" balls - 9 on each side.
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