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Drivetrain "skipping"

Old 10-21-13, 10:01 PM
  #1  
jyl
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Drivetrain "skipping"

I was climbing last Sunday and noticed, when I was standing on my lowest gear, my drivetrain was "skipping" meaning the pedal would suddenly clunk forward as if the chain had skipped. The sort of thing that makes you feel insecure and robs what little momentum and morale you have. I had to shift down a cog which made climbing even more fun. There was no problem in any other gear.

When I got home I took a cursory look at the situation. My cogs are not worn. Nor are my chainrings. My RD appears to be adjusted correctly. I can't replicate the problem riding around on the flats.

Someone suggested maybe the freewheel pawls are not engaging correctly. This is an old 7 speed freewheel, might be a Regina though I can't swear to it.

I cannot think of anything to do but drip lube into the freewheel and see if anything is different next time. Any suggestions?

Drivetrain is 53-39 and a corncobby sort of cluster, 13-23 I believe, Mavic indexed shifting, on a Cannondale frame.
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Old 10-21-13, 10:23 PM
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You could dissemble the freewheel and examine the pawls directly. But as they won't be available to replace you could do what most would do and that is throw money at it and replace the FW and chain. Or you could take the bike to a shop that is motivated and experienced for their assessment. Andy.
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Old 10-22-13, 07:00 AM
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Dont overlook the simplist reason, a stiff link in your chain.
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Old 10-22-13, 07:14 AM
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I wonder if the low limit screw is slightly too tight and the chain is not on the largest cog securely enough. A small fraction of a turn may solve the problem.
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Old 10-22-13, 07:21 AM
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I would double check the rear derailleur and the chain. It's unlikely that a pawl in the freewheel clutch is the issue.
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Old 10-22-13, 09:42 AM
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Originally Posted by Barrettscv View Post
I would double check the rear derailleur and the chain. It's unlikely that a pawl in the freewheel clutch is the issue.
+1, it's very rare for a freewheel to engage, then slip. Generally when it's a freewheel issue it manifests by failing to engage after coasting, or always slipping, even at low loads. It's also fairly rare for a worn sprocket to be the issue in low gear since ths is the least worn sprocket with the most chain wrap.

Besides the others, there's the possibility that the RD is riding too high and the upper pulley is too close to the largest sprocket, or as suggested above the trim is a bit off, or a stiff link in the chain.

Also consider the possibility that the skipping is happening up front, especially if you use the inner chainring. Front and rear skipping feel the same, and it's easy to mistake one for the other. This is a very common issue on mtn bikes where chainring wear is pretty fast.
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Old 10-22-13, 12:38 PM
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Thanks! I will look harder at the things you all have mentioned.

It would be great if the freewheel pawls were not to blame, as close ratio 7 speed freewheels don't grow on trees and I don't think I even own the correct freewheel tool to remove this one.

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Old 10-22-13, 09:41 PM
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I experienced this recently and there were two issues:
1. The wheel was not properly seated, i.e it was at a slight angle. I probably mounted it on the stand and neglected to seat it when it was on the ground.
2. The chain had several stiff links. I used that chain last winter and recently put it back on. It had been cleaned and lubed and had been waiting its turn but apparently was not savable.
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