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I just ripped apart my mom's mountain bike's rear hub. One of the bearings was incredibly rough, so I replaced it, and the other one was smooth, but didn't turn very easily. Since I didn't have a replacement for it on hand, I just put it back, but I'm not sure if I should try to replace it. Is there a good rule of thumb on bearings? Does one failed bearing imply that another one is likely to go soon?

While we're at it, should I be doing anything to the freewheel other than cleaning it and re-greasing it? I've heard it's important not to put too much grease inside the freewheel, or it'll increase drag when you're coasting, so I was careful of that.

The specifics for this bike:

  • Mavic wheels
  • Shimano 9-speed freewheel
  • Full suspension mountain bike that gets fairly heavy use on XC singletrack terrain
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It's unclear what you mean by "one bearing". If, within a single bearing assembly, there is one ball that appears pitted, all balls should be replaced. You should never (except in emergency situations) replace some of the balls in a bearing and not others. But if, say, the front hub bearings have gone bad and the hub needs replacing, that says nothing about the condition of the rear hub or other bearings on the bike. – Daniel R Hicks Jun 7 '15 at 0:26
up vote 8 down vote accepted

According to Lennard Zinn, you should replace all of the bearings even if only one is obviously bad. That way you ensure round, smooth, consistent bearings. I've been using his repair manuals for years and he's pretty much never steered me wrong.

[Edited to repair the link]

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Above link has an error/not found. Here is the link without 404 error not found. [] – Akshay Aug 2 '13 at 23:20

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