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New chain/pulling derailleur
#1
Hey all,
Love this site. I have a 10 year old Trek 6000 that has a Deore LX rear derailleur. I recently replaced the original chain with a new SRAM chain. It went on fine and I did some slight adjustments on the derailleur, lubed it up and took the bike for a test ride. It's so smooth and quiet now. However, I'll be riding along fine and all the sudden I'll hear the derailleur being pulled and then snapping back into position. It's not much of a pull because I don't really feel it, I only hear it. There is no pattern to it and it doesn't necessarily do it when I'm pedaling fast or slow or hard up hills or anything. It just does it randomly. A couple times it pulled the derailleur enough that the chain got caught up in the bottom section of my front derailleur and I was forced to stop. When I first installed the new chain, I broke the chain at the same length of the old one and installed it without a quick release link. I rechecked the chain and the pins are all set ok and don't appear to be sticking out too far that they would catch anything. Also, I hung my bike in the garage and just went through the gears by hand and couldn't replicate the problem so it's like it only happens under load. Any ideas?

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#2
Chain suck?
Due usually to a worn chainring.
The chain "hangs" on the chainring teeth and winds around it.
In the early stages of wear the chain hangs but is released as the derailleur pulls it off.
That's when you can hear the derailleur swing back.
As it gets worse the chain doesn't release and winds around finally jamming against the front derailleur.
Usually only does it on one chainring though - the one most used.
Fitting a new chain has shown it up.
For an explanation:-
http://fagan.co.za/Bikes/Csuck/

[font=Trebuchet MS]Ride hard or ride home alone![/font]
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#3
That could very well be it. I noticed the largest chain ring has worn quite a bit. The old chain and current chain ring wore together so it wasn't an issue. Not the case with the new chain. Amazingly enough the cassette doesn't look worn at all. I always thought they would go before the chain rings.

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#4
trekcy,
Chainrings will certainly wear slower than the cassette rings due to less rotation during use – you probably don’t use the smaller chainring a lot. I fully agree with cycler’s suggestion – worn chainring…
Does it work fine on the other chainrings (I’m presuming three; therefore smallest and middle) …? I replaced the rear (9sp) cassette and chain and suffered very similar problems to what you are describing (including everything working fine when not under load) when on the middle chainring: Replaced that and everything’s hunky…

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#5
I don't use the middle chain ring much at all. At least not lately. I usually just commute now so the large chain ring is my choice. I tried switching to the middle chain ring to test things and it almost sticks more to the middle one. I did my first commute tonight, albeit gingerly and was on the large chain ring and had the chain stick to the chain ring about a dozen times over 2 miles with it twice getting up into the front derailleur. I'll take a closer look at my middle chain ring to see about wear on it. The large chain rings teeth are getting pretty pointy looking but the cassette - which has never been replaced - still looks fine.

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