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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 01-06-06, 02:00 AM   #1
xtr_trek
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What bottom bracket to buy? Opinions?

Hey,

I do a lot of nasty wet muddy riding and have been going though generic Shimano XT bottom brackets like there's no tommorow. When I pull them out they are always gummy and full of gunk. Anyone have a reccomendation on another BB that is a little more durable/resistant? I need it for an XT crank, so it has to be available in octalink. Is the XTR BB any better?

Thanks for any help,
-Andrew
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Old 01-06-06, 02:13 AM   #2
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I don't know, honestly, and I just ride road so haven't had to deal with this sort of worry, but I'll be interested to hear what comes of this thread.
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Old 01-06-06, 03:03 AM   #3
Robert Gardner
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I don't understand what you are talking about? On my bike the Shimano BB are essentially sealed from contamination such as you describe. Even unsealed BB would not get full of gunk.
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Old 01-06-06, 09:00 AM   #4
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@xtr_trek, do you mean that the bearings are shot on the XT bottom bracket? You can get gum and gunk into your frame by riding in the mud, possibly, but the gum and gunk that hurts the bottom bracket bearings wouldn't be stuff that you can see. You could pull the BB and cosmetically clean it, if the bearings are okay. And even if they aren't, with a sealed cartridge (non-serviceable, internally) unit, you may as well ride it into the ground or until it provides actual resistance to pedaling. You won't endanger your frame by doing so.
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Old 01-06-06, 02:22 PM   #5
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Yeah, the gunk on the inside of the frame doesnt bother me. But it seems like some gunk has gotten past the seals, and gone right inside. I could be wrong. It's built up around the actual spindle, in the crack between the spindle and the cartridge.

It is possible that the stuff hasn't made it inside, I may just be overreacting to a little dirt!

I never noticed it when pedalling, but when I pulled this one out, it doesn't feel "like it should" to me... How much resistance should the BB have before it is worn? it turns, but shouldn't I be able to spin it and have it keep spinning, or is it normal to be a little tight?

Any help with this would be great, I really know nothing about bottom brackets! (as you can probably tell)

-Andrew
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Old 01-06-06, 02:56 PM   #6
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If you can spin the spindle in your fingers without too much resistance (even if you can feel a little grit), it'll be fine for pedaling. I think that you need to ride your bb's into the ground a bit more (and perhaps a lot more) than you are. Have you saved all of your old ones?
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Old 01-06-06, 03:22 PM   #7
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I've used XT Octalink bbs on two different bikes, the first one when Octalink was first introduced. Never had a problem, and in fact they seem incredibly durable to me-
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Old 01-06-06, 04:48 PM   #8
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I use the generic Shimanos and I can't seem to kill them no matter what I do.
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Old 01-06-06, 04:57 PM   #9
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When the crank is attached to the bottom bracket, without the chain on, it should spin freely and smoothly. When the crank is not attached to the bottom bracket, and you are turning the bottom bracket spindle with your fingers, there is more resistance but it should still be smooth.
In my experience the cheapo shimano bottom brackets are good for at least 5000 miles, including insanely wet mountain bike excursions when the bottom bracket is occasionally submerged.
I do not have any experience with octalink or ISIS bottom brackets. I have heard they have shorter bearing life compared to a traditional square taper bottom bracket because they are forced to use smaller bearings. I don't know if this is true, and I would be interested in other riders opinions on this, as I am currently building a cyclocross bike with an ISIS bottom bracket.
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Old 01-06-06, 04:58 PM   #10
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no BB should keep spinning by itself if you turn the spindle with your fingers. You may be overreacting. As long as the bearings aren't crunchy and spin smoothly you should be fine. If you're always in the water, your frame may be flooded which would bathe the BB in swamp water. Try drilling a 1/8 inch hole in the BB shell to allow the gunk to drain.
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Old 01-06-06, 05:26 PM   #11
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Quote:
Originally Posted by thekorn
When the crank is attached to the bottom bracket, without the chain on, it should spin freely and smoothly. When the crank is not attached to the bottom bracket, and you are turning the bottom bracket spindle with your fingers, there is more resistance but it should still be smooth.
In my experience the cheapo shimano bottom brackets are good for at least 5000 miles, including insanely wet mountain bike excursions when the bottom bracket is occasionally submerged.
I do not have any experience with octalink or ISIS bottom brackets. I have heard they have shorter bearing life compared to a traditional square taper bottom bracket because they are forced to use smaller bearings. I don't know if this is true, and I would be interested in other riders opinions on this, as I am currently building a cyclocross bike with an ISIS bottom bracket.
I've got an old road bike with a Nashbar ISIS bb in it, with a couple thousand miles on it so far, absolutely no problems. I've used the heck out of Octalink bbs on mountain bikes, with my share of creek crossings, all-day mud, etc. and I've yet to wear one out. When the Octalink/ISIS stuff first hit the market, it seemed like there was a lot of negative feedback on the ISIS bbs, presumably because of the smaller bearings, like you say. Personally, I've got nothing but good things to say about Octalink, and so far I'm very pleased with the ISIS bb I'm using-
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Old 01-06-06, 06:25 PM   #12
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I put the bottom bracket in my new frame. It seems fine. I think I was just overreacting, it's a little worn but you don't notice it at all once its in the bike. Thanks guys!
-Andrew
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Old 01-06-06, 10:29 PM   #13
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By an XT.....if it ain't broke don't fix it. They are dependable and hold up well. Have had originals in a couple bikes both riden often and going on 5 plus years.
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