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Chain jams - how do I describe this problem to be able to search?

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Chain jams - how do I describe this problem to be able to search?

Old 11-29-10, 01:26 PM
  #1  
rojeho
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Chain jams - how do I describe this problem to be able to search?

I have experience fixing cars and karts, but new to bicycle mechanics. I can search, but I need help with the terminology to know what this issue is.

I bought a 2005 Specialized Dolce for my wife. PO claimed that it was ridden six times, and it looks like that could be accurate. It has Sora brifters, Sora FD, Tiagra RD, Sora 8sp cassette and Shimano HG-50 chain.

I will do a search for a good maintenance book, but if you would like to offer up your favorite that would be great.

For the first good tune up service, should I learn on the first one or let my LBS go through it for the first one?

The bike has two problems. The first is that while riding it will jump gears on the cassette. I cannot duplicate this under no load on a stand.

The second problem is that any time the pedals move backwards, the chain will jam on the cassette. On a stand if I move the pedals very slowly, I can see that it looks like the chain is walking off axis and may be hitting something on the FD. I didnít look close enough to tell if this was happening or not. I donít know how to describe this in the right terminology to begin searching.

Thanks for the help.
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Old 11-29-10, 01:55 PM
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1. Usually can be fixed by adjusting the barrel adjuster on the RD. Other than that it could be a slightly bent RD.

2. Might need some maintenance on the free hub. Could be some old grease in there that's not allowing it to spin backward freely.
I once had a similar experience with a used bike and it just turned out to have a chain that was too long. I removed 2 links and it was fine. Just not taught enough I guess.

I'm sure there are other people with more insight than me, but that's what I'd start with.
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Old 11-29-10, 02:27 PM
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Sounds like a little maintenance as the poster above suggested. Check out the info below.


Decent book for starters - - https://www.amazon.com/Bicycling-Maga.../dp/1579540090
Also, google search will find youtube videos and bicycle tutor sites.
Park Tools site has a ton of free info as well https://www.parktool.com/blog/repair-help
And last but not least. The master of information - https://www.sheldonbrown.com/
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Old 11-29-10, 02:28 PM
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Try parktools.com for help. Their website cover this very well.
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Old 11-29-10, 02:42 PM
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With drive train issues in particular it is very difficult to determine what the problem(s) might be when you are not accustomed to repair or terminology, and there may be multiple issues. Unless you do not value your time at all I would suggest taking the bike to a shop, get an estimate on repair and if affordable have them do it. Much easier to learn to work on a bike when it starts out properly adjusted and with issues like bent, worn or misaligned parts addressed.
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Old 11-29-10, 03:03 PM
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1. sounds like the rear derailuer cable needs to be tensioned as tober1 suggested. barrel adjuster is located on the rear derailuer where the cable housing is connected to the derailuer.

2. you may be cross chaining when back pedaling. cross chaining is where the chain is on the large front chainrings and large rear cogs or small front chain ring and small rear cogs. Since there isn't a derailuer to hold the chain in line when back pedaling it will try to go in a straight line from the front chainring.

try back pedaling when in the small front chainring and large rear cog and see if it still jams.
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Old 11-29-10, 03:13 PM
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Originally Posted by cyclist2000 View Post
2. you may be cross chaining when back pedaling. cross chaining is where the chain is on the large front chainrings and large rear cogs or small front chain ring and small rear cogs. Since there isn't a derailuer to hold the chain in line when back pedaling it will try to go in a straight line from the front chainring.

try back pedaling when in the small front chainring and large rear cog and see if it still jams.
I will try this but I have the feeling the problem is bigger than this. Rotating the pedal less than a quarter turn (like to get the pedal set in position to get started) is enough to jam. Moving the pedal by hand it takes 1-2" of chain movement before I can see that it doesn't look right. I will make sure that both gears are in the middle of the ranges before trying this again.
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Old 11-29-10, 04:38 PM
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thread on back pedaling problems

back pedaling problem

second thread

You may want to provide as much information as possible for the back pedal problem and some photos of the chain jamming might help diagnose the problem.

another cause of this problem may be due to the derailuer hanger being bent or out of alignment.
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Old 11-29-10, 05:02 PM
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Sounds like the rear derailleur hanger may be bent, this can cause the chain to creep across the cogs on the cassette.
Also go to www.sheldonbrown.com and search for "auto-shifting".
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