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Chain/derailleur snag problem
#1
Hello, this is apparently an odd problem for which I can't find any information on, so I thought I'd post on a forum and see if you can help Smile

This problem could be relevant in this subforum or the Derailleur subforum, I'm not actually sure where the problem lies.

Once per revolution of the chain I get a brief drop in tension. On the pedals it feels like the chain has skipped, however it's not at all violent and it is completely predictable when it will happen - once every three revolutions of the pedals in the gear I use most often.

It's hard to be totally sure, as it seems to come and go. I first started getting it right after being forced off a path onto some rough grass in a park (how I love oblivious dog owners), it was rough enough that I nearly lost control completely - I have a Trek 7.3 (hybrid) bike. The shaking was huge and immediately after I noticed this problem. It seemed to sort itself out when I got off and wound the pedals around to have a look what was going on, however a week later it now seems to rear its ugly head whenever it feels like it, at seemingly no change in input from me. I can ride a few miles without it occurring only for it to suddenly start again, skipping forward every three pedal revolutions, like clockwork.

The fact that it always occurs at regular, repeatable intervals (when it's happening at all, I seem unable to control that aspect), suggests it is a problem with the chain rather than anything else. Upon closer inspection it seems that it's catching the back derailleur - every once around the chain it appears to snag the derailleur very slightly, causing it to kick back on its spring. I thought perhaps it was an out-of-line link, but I've very carefully inspected the chain links around the point in the chain where I get this derailleur kick and I can't see a thing. Admittedly, one of those links is the fastening link (it's one of those chains with the masterlink that you pinch together to undo etc). I've double checked this masterlink to no effect.

Other details should they help; it's not chain wear, this is a new chain (no more than 200miles ridden on it so far). I replaced the chain and cassette at the same time, drive train in general has been flawless up until this started occuring. It isn't slipping between gears and the skip happens regardless of which cog/chain ring I'm on. When I changed the cassette/chain I also thoroughly cleaned out the crud around the derailleur so I don't think it's originating there. I keep the chain clean and lubricated - I'm commuting on the bike, so it's never put through too much stress and I look after it.

I'm not sure what I should be looking for. Having inspected the chain links I can't see a thing but maybe I'm not looking for the right thing.

Any suggestions/help would be much appreciated!
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#2
I want to say that it is probably a stiff link. Long process but I would check each one. Here is a video to assist you http://bicycletutor.com/stiff-chain-link/
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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#3
(06-02-2010, 10:58 AM)Bill Wrote:  I want to say that it is probably a stiff link. Long process but I would check each one. Here is a video to assist you http://bicycletutor.com/stiff-chain-link/

Bingo.

[attachment=964]

None of the other links remain in that position once I let go. I was indeed looking at the right link, just not for the right thing. Twiddling had no effect but I've commandeered a colleague's chain-splitter so here's hoping.

Many thanks.
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