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Concerning the ball bearings from a hub I'm servicing

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Concerning the ball bearings from a hub I'm servicing

Old 08-18-10, 08:23 AM
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Plimogz
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Concerning the ball bearings from a hub I'm servicing

Hi there,

I've opened up the front bontrager hub on my bike and have noticed that all of the balls from the disc side bearing are noticibly tarnished compared to those from the non-disc side, which are still nice and shiny.

Also, the grease from the shiny, non-disc side was still clean and green, whereas the other side's grease was brown and filthy. Any thoughts?

I've cleaned everything off and I'm wondering if this is the kind of situation which would ideally call for new shiny balls for the disc side. And if so, what size balls should i go looking for if I want to stock up? Any tips on measuring ball bearing ball with a caliper? Imperial or Metric? So many questions...

The hub is stock from a 2008 Fisher Rig.
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Old 08-18-10, 08:39 AM
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The discoloration might be from heat related to braking, though I'm not sure that much is conducted down to the hub, the way it is on automotive brakes.

Either way I make it a practice to replace the balls (ball bearing is the entire system including both races and the balls) whenever I service bearings. You might as well buy Grade 25 balls which are those used in elictric motor bearings and are as good or better than the originals. It might be overkill in quality, but the price premium over lower quality balls is very small.

Sizing is easy, they're made in fractional inch sizes with 1/4", 3/16" and 5/32" being the most common, so any caliper will be good enough to identify the size.
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Old 08-18-10, 08:45 AM
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Balls are cheap, it's a good practice to change them everytime you overhaul your hub. The most common size for front hub balls is 3/16", but take one to your lbs to check the size.
Maybe the dustcap was not properly seated on one side of your hub hence the dirty grease.
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Old 08-18-10, 09:03 AM
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Ok, many thanks for the replies!

Upon further inspection, the cone from the tarnished disc side shows signs of deterioration and I suppose the balls would evince the same if I really inspected them thoroughly.

@ValVal: I've taken a caliper to the balls and come up with 0.186". Do you think that I am correct in assuming that the roughly 0.001" difference between what I came up with and what you said was the most common size (3/16") is up to inaccuracy on my part? Do you think it would be a safe bet to try some 3/16" balls in there?

...Especially considering that I know exactly where to go get some right this minute... Yay Harsupco!!!
Thanks again for that, btw

edit: Do you know where I might get some new cones too? while I'm at it, y'know.

Last edited by Plimogz; 08-18-10 at 09:06 AM. Reason: added something
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Old 08-18-10, 09:24 AM
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Originally Posted by Plimogz View Post



I've taken a caliper to the balls and come up with 0.186". Do you think that I am correct in assuming that the roughly 0.001" difference between what I came up with and what you said was the most common size (3/16") is up to inaccuracy on my part? Do you think it would be a safe bet to try some 3/16" balls in there?

edit: Do you know where I might get some new cones too? while I'm at it, y'know.
It's definitely caliper reading error (just try to buy .186 balls), so buy the 3/16" with confidence.

Cones are a different problem because they're hub specific, so you'll have to try to locate one through bike sources. Replacements for the ones on better hubs are generally available, but those for low end brand-X may not be. If you can't find an exact same brand match, visit the LBS and they might have an analog, since many hub makers buy the cones from others.
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Old 08-18-10, 09:32 AM
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Thanks FB!

I guess I'll be going round the bike shops again. So be it, the weather's nice.
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Old 08-18-10, 09:40 AM
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I think La Cordée carry a bunch of generic cones, they might also be able to order the specific cones for your hub, or not...
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Old 08-18-10, 10:00 AM
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I wonder if brake dust got into the bearings. We've all seen the dust and discoloration on the wheels of cars from the brake pads of disc brakes and I wonder if similar wear particles could have gotten into the OP's hub bearing past a poor seal.
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Old 08-18-10, 10:05 AM
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it sounds like dirt/dust got into the bearings on the brake side. whether or not this is related to the brake being on that side, is another question.
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Old 08-18-10, 10:06 AM
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The brown sludge in the grease on that one side sounds to me as though the seal wasn't working well and you got some water into the disc side. Once that happened and it pitted the balls and cone then the size difference could well be from wear. Iron oxide is a poor grinding media but it's still abrasive enough to wear away a thou worth over time.

When you get the new balls measure them with your caliper again. I'll bet they are spot on or near enough.

And a hint for you. If it's a dial or digital caliper you have be sure to wipe the jaws clean where they come together before zeroing the dial or readout. Even enough airborne dust on the jaws can hold them apart by a thou or two. And then when you measure a point contact item such as bearing balls that push the crud to the side you'll come out that much short of the true measurement. Again, you can test this for yourself. Just zero up the caliper first and then wipe the jaws clean. If there was something there the reading will be slightly minus. Or if you have a dial caliper then be sure the jaws are spotless before you zero the dial the first time. From there dirty jaws will show as a measurement a thou or so above zero.
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