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drivetrain issues continue

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drivetrain issues continue

Old 06-07-07, 11:35 PM
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fadetoblack6902
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drivetrain issues continue

my raleigh m80 mtn bike developed a bad chain skipping problem in the small cog/ middle chainring combo. It got to the point that it would skip while spinning the pedals on the repair stand. Other than that, the bike rode and shifted flawlessly. I had a slightly bent middle chainring, so I replaced that. I then replaced the prematurely stretched chain (maybe 600 miles on it) and the chain skip was much better, but still skipped under a VERY heavy load.

The second I installed the new chain the shifting went to hell. when the cable is tensioned properly, the chain will shift up to larger cogs fine for the most part, but will hesitate between the 3rd and 4th smallest cogs. The chain is VERY hesitant to come down into smaller cogs though. Sometimes it won't go down at all. When riding the bike and shifting down, the chain skips randomly over the gears. very bad. When the chain is undertensioned the chain will go down into smaller gears perfectly, but obviously won't come back up.

What I have done:

I replaced the shift cable and lubed it up. The cassette has been cleaned. The spring in the derailleur and all pivot points have been thouroughly lubed with tri-flow. This is definately not an adjustment issue, both myself and my friend who has been a touring cyclist manager for 20 years could not get it adjusted correctly. The derailleur hanger was very slightly bent, but it is now straight. I tried it with a different wheel with a brand new cassette on it and both problems were still there.

My original chain was a sram pc-49, the new one is a sram pc-951. the cassette is a sram pc-950. Could there be a compatability issue? I did have to shorten the chain by 2 links from the old chain's length because with the old length on the large cog/small chainring combo there was absolutely no chain tension.

both myself and my mechanic friend are completely stumped. any help is greatly appreciated.
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Old 06-07-07, 11:40 PM
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When you straightened the hanger, did you use an alignment tool or just an eyeball and crescent?
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Old 06-07-07, 11:42 PM
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Originally Posted by Wordbiker
When you straightened the hanger, did you use an alignment tool or just an eyeball and crescent?
my mechanic just eyeballed it, but he said it was barely bent in the first place. The hanger definately did not get bent while changing the chain, so I doubt this is the issue.
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Old 06-08-07, 12:24 AM
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No, I wasn't stating you had, just that without an alignment tool, even my trained eye has been fooled. Eying for plumb is only half of it...the hanger can be twisted and it is very hard to see without a proper tool.
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Old 06-08-07, 12:59 AM
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"I did have to shorten the chain by 2 links from the old chain's length because with the old length on the large cog/small chainring combo there was absolutely no chain tension."

Put it on big:big. Pull excess slack out of the chain. How many links excess? Anything over 1 Full + any partial link SETS is excess. IOW <2 link sets.
You just may not have ENOUGH chain tension.
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Old 06-08-07, 06:46 AM
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Originally Posted by Bill Kapaun
Put it on big:big. Pull excess slack out of the chain. How many links excess? Anything over 1 Full + any partial link SETS is excess. IOW <2 link sets.
You just may not have ENOUGH chain tension.
Concur.
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Old 06-08-07, 08:03 AM
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so you're saying put it on big big, and see how many extra links are taken up when you pull the chain tight?
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Old 06-08-07, 08:27 AM
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I have been having a similar issue. Everything is properly adjusted, shifts up to larger cogs fine, but is reluctant to shift down to the smaller cogs. Or when I put a lot of load on the drive train it will auto shift to a smaller cog. Reading one of Sheldon Brown's articles I think my issue is due to friction, even though I have a new cable and everything is clean and lubed. It may be due to using spiral cable housing versus proper shift cable, although the cheap Bell cables never gave me trouble on my other bikes. I have new housing but haven't installed it yet, I am hoping it will fix my problem.
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Old 06-09-07, 08:07 AM
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well I may be buying an xt derailleur and some xt shifters cheap so i'll throw those on and see if that solves the problem. If that along with new housings doesnt help I dont know what will
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Old 06-09-07, 08:22 AM
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Originally Posted by bfromcolo
It may be due to using spiral cable housing versus proper shift cable, although the cheap Bell cables never gave me trouble on my other bikes. I have new housing but haven't installed it yet, I am hoping it will fix my problem.
Spiral cable will compress, should not be used for shift cable. Replace that cable, & if you've done everything else correctly, your problem will most likely be solved. Hard to believe you mechanic was stunned when brake cable didn't function correctly when being used as shift cable, or did he know? Here's a link that might be helpful:
http://sheldonbrown.com/derailer-adjustment.html#chain
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Old 06-09-07, 01:04 PM
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Originally Posted by fadetoblack6902
so you're saying put it on big big, and see how many extra links are taken up when you pull the chain tight?
How else would you interpret it?
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Old 06-09-07, 03:11 PM
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Originally Posted by fadetoblack6902
so you're saying put it on big big, ...
That's big-big without going through the dérailleur.
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Old 06-09-07, 10:32 PM
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Originally Posted by freeranger
Spiral cable will compress, should not be used for shift cable.
If it's an older friction shifting bike, yes it can & should be used.

Sorry, just had to say it. Most of my bikes are friction, and only a couple are indexed.,,,,,BD
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Old 06-09-07, 11:50 PM
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Originally Posted by Bikedued
If it's an older friction shifting bike, yes it can & should be used.

Sorry, just had to say it. Most of my bikes are friction, and only a couple are indexed.,,,,,BD
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Old 06-10-07, 01:47 AM
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I replaced the housings, and now the shifting is perfect under normal loads. But under very heavy loads the chain is now skipping in all gears. You really have to mash on the pedals, but it feels like the chain is not meshing well with the gears. am I back to the cassette?
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Old 06-10-07, 03:24 AM
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Originally Posted by fadetoblack6902
my raleigh m80 mtn bike developed a bad chain skipping problem in the small cog/ middle chainring combo. It got to the point that it would skip while spinning the pedals on the repair stand. Other than that, the bike rode and shifted flawlessly. I had a slightly bent middle chainring, so I replaced that. I then replaced the prematurely stretched chain (maybe 600 miles on it) and the chain skip was much better, but still skipped under a VERY heavy load.
Chains don't normally stretch prematurely they stretch acording to the loads they endure.

Lets size it up.

600 miles

The chains stretched

The 11T cog skips

And the middle chainring needs replacing.

Sounds like you might have been mashing the big gear a bit and worn it out.

Have you checked the cog isn't worn as this is the most common reason for new chains skipping.
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Old 06-10-07, 09:09 AM
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I have looked at the cog, and it doesn't really look worn. my mechanic doesnt think so either.
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