"Rough" drivetrain diagnosis needed.......
08-15-06, 06:21 PM
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"Rough" drivetrain diagnosis needed.......
I have a 1998 GT Timberline frame (chromo) that I like. Had a 7-spd drivetrain, decided to chg to 8.
Put on XTR 12-32 cassette on an LX hub, Mavic rims, Alivio der., new 8 spd rear shifter, SRAM PC-58 chain. Shifts fine, but is rough when in 8th (smallest cog) and 2nd or 3rd front gear (larger cogs). The 7 and 8-spd hub seem to be same width. The only thing I've noticed is if I turn the cranks backwards, there is a sound which sounds like it comes from the freehub, like rough bearings, kind of a pop-pop. If I take tension of of the rear der.arm, so not much chain tension on the cassette, does not seem to do it. With the wheel off, the freehub seems smooth enough, but other than the freehub bearings needing lube, I can't think of what it could be. Anyone?
Put on XTR 12-32 cassette on an LX hub, Mavic rims, Alivio der., new 8 spd rear shifter, SRAM PC-58 chain. Shifts fine, but is rough when in 8th (smallest cog) and 2nd or 3rd front gear (larger cogs). The 7 and 8-spd hub seem to be same width. The only thing I've noticed is if I turn the cranks backwards, there is a sound which sounds like it comes from the freehub, like rough bearings, kind of a pop-pop. If I take tension of of the rear der.arm, so not much chain tension on the cassette, does not seem to do it. With the wheel off, the freehub seems smooth enough, but other than the freehub bearings needing lube, I can't think of what it could be. Anyone?
08-15-06, 06:33 PM
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Originally Posted by freeranger
I have a 1998 GT Timberline frame (chromo) that I like. Had a 7-spd drivetrain, decided to chg to 8.
Put on XTR 12-32 cassette on an LX hub, Mavic rims, Alivio der., new 8 spd rear shifter, SRAM PC-58 chain. Shifts fine, but is rough when in 8th (smallest cog) and 2nd or 3rd front gear (larger cogs). The 7 and 8-spd hub seem to be same width. The only thing I've noticed is if I turn the cranks backwards, there is a sound which sounds like it comes from the freehub, like rough bearings, kind of a pop-pop. If I take tension of of the rear der.arm, so not much chain tension on the cassette, does not seem to do it. With the wheel off, the freehub seems smooth enough, but other than the freehub bearings needing lube, I can't think of what it could be. Anyone?
Put on XTR 12-32 cassette on an LX hub, Mavic rims, Alivio der., new 8 spd rear shifter, SRAM PC-58 chain. Shifts fine, but is rough when in 8th (smallest cog) and 2nd or 3rd front gear (larger cogs). The 7 and 8-spd hub seem to be same width. The only thing I've noticed is if I turn the cranks backwards, there is a sound which sounds like it comes from the freehub, like rough bearings, kind of a pop-pop. If I take tension of of the rear der.arm, so not much chain tension on the cassette, does not seem to do it. With the wheel off, the freehub seems smooth enough, but other than the freehub bearings needing lube, I can't think of what it could be. Anyone?
-Kurt
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08-15-06, 06:40 PM
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The wheelset was new-made for 8/9 spd cassette. Usually I'm fairly decent at diagnosing a problem, but this one's got me! The only other thing I noticed (forgot to mention) is that high gear sits further out (closer to the chainstay) on the 8-spd cassette. But the chain is not rubbing or catching on anything!
08-16-06, 10:55 AM
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Well, at least now I don't feel so bad about not being able to figure it out. Think it is a chain clearance thing, maybe. When I release pressure on the rear der. "arm", it stops, so I think the side plates of the chain may be slightly rubbing the next cog. Don't know why-not a bad angle, especially with largest cog front and smallest rear cog. Might try a small spacer between 8th and 7th. What have I got to lose?
