need help - Chain snags on larger cog
04-28-06, 09:04 AM
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need help - Chain snags on larger cog
Hi, I'm new to this forum and am returning to cycling after approx. 10 years and I need some help.
I just finished restoring a 20+ year old Centurion Accordo. I put on a Shimano 105 CS rear derailleur, which is supposed to be 6 speed compatible. Anyway, the first 10 miles or so everything worked fine then I started feeling chain slip. Let me just say that the bike has the original 6 speed Uniglide freewheel, the one with all twisted teath(by design for easier shifting). I picked the bike up and turned the crank by hand and noticed that if the chain was on any cog other than the largest it would momentarely snag on the top of the larger cog next to it. The shifting is correct and it shifts fine to the correct cog, but the larger cog snags the chain and drops it, snags it and drops it, and so on. Could this be caused by the chain or freewheel. Let me just say that it happens the chain is any cog accept the largest, obviously, and if it was a freewheel problem than it would mean that all the cogs are bad, is that even possible?
Any and all help is greatly appreciated.
One other question. If I do need a new freewheel, can I replace my 6 speed with a 7 speed, or will I need a new hub and shifter(currently Shimano downtube SIS shifter)?
I just finished restoring a 20+ year old Centurion Accordo. I put on a Shimano 105 CS rear derailleur, which is supposed to be 6 speed compatible. Anyway, the first 10 miles or so everything worked fine then I started feeling chain slip. Let me just say that the bike has the original 6 speed Uniglide freewheel, the one with all twisted teath(by design for easier shifting). I picked the bike up and turned the crank by hand and noticed that if the chain was on any cog other than the largest it would momentarely snag on the top of the larger cog next to it. The shifting is correct and it shifts fine to the correct cog, but the larger cog snags the chain and drops it, snags it and drops it, and so on. Could this be caused by the chain or freewheel. Let me just say that it happens the chain is any cog accept the largest, obviously, and if it was a freewheel problem than it would mean that all the cogs are bad, is that even possible?
Any and all help is greatly appreciated.
One other question. If I do need a new freewheel, can I replace my 6 speed with a 7 speed, or will I need a new hub and shifter(currently Shimano downtube SIS shifter)?
04-28-06, 09:08 AM
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Your indexing is off. It's shifting just a little too "high" for each gear, and so it wants to shift but can't quite do it. Probably exacerbated by this freewheel, but unless it's worn you should be able to make it work.
04-28-06, 10:41 AM
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Well, the chain is trying to shift up but not quite doing it, which means it's not sitting in the right place with respect to the "center" of that gear. This is pretty much the definition of messed up indexing. If you're totally sure that the indexing is right, you might have a bent RD/hanger.
05-08-06, 06:01 AM
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While trying to adjust the indexing I noticed that the problem was not that the chain was catching on the next larger cog but that the chain (for lack of a better description) was actually bunching up at the top of the cog and it happened at all six speeds. I'd like to appologize for the previous incorrect description of the problem, but that is what I thought I saw. At closer inspection it appears that the teeth are catching the chain either a link too late or between links and causing the chain to bunch up towards the top and then release causing what feels like the chain is slipping. I was able to recreate this problem easily and the slower I turned the crank the more often it happened. Is this a bad chain or bad freewheel?
Thanks;
Thanks;
05-08-06, 07:08 AM
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It sounds like either the chain or freewheel are worn, possibly both. Are they original? Uniglide freewheels were not designed for index shifting IIRC, and the 6-speed derailleur may not have been either.
Indexing derailleurs have a "floating" top pulley that adjusts for slight misalignments, If your derailleur doesn't have this feature the indexing will be nearly impossible to adjust reliably.
Indexing derailleurs have a "floating" top pulley that adjusts for slight misalignments, If your derailleur doesn't have this feature the indexing will be nearly impossible to adjust reliably.
05-08-06, 07:21 AM
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The derailleur is new, Shimano 105 CS and it is SIS. The chain and freewheel are original, If I replace both chain and freewhell can I change the freewheel for a non uniglide six speed or does it have to be an exact replacement?
05-08-06, 07:40 AM
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I think you are going to have indexing problems with any 6-speed freewheel since they weren't designed with indexing in mind and the cog spacing isn't even. If you can use your shifters in friction mode the problems should disappear.
05-08-06, 08:02 AM
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I hate to dissagree with you but the original shifter and derailleur are indexed. I only replaced the original derailleur because the spring bracket is broken.
05-08-06, 08:05 AM
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If you have a 20 year old chain and freewheel, I would seriously think about replacing both of them.
05-08-06, 08:47 AM
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OK, I can change both. Again can I replace the freewheel with a different model/brand or does it have to be an exact replacement?
05-08-06, 08:55 AM
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Originally Posted by MartyZ
I hate to dissagree with you but the original shifter and derailleur are indexed. I only replaced the original derailleur because the spring bracket is broken.
I assume the original shifters and freewheel are both Shimano. If either are a different maker, that would explain why the new derailleur won't work properly. You are going to have a tough time being fussy about the freewheel model you replace it with as the selection is now rather limited.
