Maybe unusual chain slip...

[Tin Pot]

1. Chain skips only under force, mostly in the lower gears/larger sprockets when climbing.

2. Shifting is fine in the work stand.

3. Chain is not elongated.

4. Sprockets are not worn.

The only thing I can think of now is cleaning the chainset as it's a bit mucky.

My Zinn book talks about derailleur bends and jockey wheels but I don't think this would match the symptoms - though I'll tighten the jockey wheels on the off chance.

Any other ideas?

Ta, TP

 

[S-Express]

3. Chain is not elongated.

4. Sprockets are not worn.

One of those two is unlikely to be correct..

 

[Yellow Saddle]

Define slip.

Does the chain skate over the top of the sprocket teeth or does the chain skip between adjacent sprockets?

 

[Welsh wheels]

I'm not technical, but in my experience a clean chain is a happy chain.

 

[Tin Pot]

Define slip.

Does the chain skate over the top of the sprocket teeth or does the chain skip between adjacent sprockets?

Over the top.

I'd call it skipping if it were changing sprockets.

 

[Tin Pot]

[QUOTE 4898626, member: 9609"]you're chain may not be slipping. - pawls in free wheel hub are not engaging fully[/QUOTE]

Not sure what you mean by this, can you clarify?

 

[Tin Pot]

Over the top.

I'd call it skipping if it were changing sprockets.

Hang on. That can't be right.

I'm going to have to ride it again to check!

 

[S-Express]

[QUOTE 4898626, member: 9609"]you're chain may not be slipping. - pawls in free wheel hub are not engaging fully[/QUOTE]

If that were the case, it would be doing it in all sprockets, not just the top few..

 

[raleighnut]

Have you removed the jockey wheels and refitted them the wrong way up (the top one is different to the bottom one) DAMHIKT

 

[screenman]

Rear mech alignment.

 

[Yellow Saddle]

Over the top.

I'd call it skipping if it were changing sprockets.

Over the top is skating. Left and right and left and right is skipping.
How long is the chain over 12 links?
If the shifting is fine in the work stand, is it fine on the road? If yes, then suspect skating and this is easy to replicate. Find a steep hill, shift to suspect gear and push hard. If it skates, you have an out-of pitch sprocket. Time for a new cassette.

 

[gaijintendo]

I had that on the bike I built because I had failed to tighten my chainset sufficiently with the hollowtech 2 star nut thing. I didn't have the tool.

 

[gbb]

[QUOTE 4898759, member: 9609"]the lower gears are where the most pedal pressure is exerted (it is with me anyway)

I had a friend with similar problems to OP, I tried my old free wheel hub in it and it cured the problem so he bought a new one. This wasn't so much skating as sudden jumps but it was only happening when a lot of effort was sudenly applied after changing gear. he thought it was chain slipping.[/QUOTE]
Certainly on my at the time relatively new Bianchi, it slipped occasionally, usually in the top gears but not exclusively. It was the freehub. It happened maybe 10 times over a few months then settled/stopped, never to return.
Ops experience of it happening only in the high gears may be simply that's when it happened to happen, not that it's the only gears when it may happen.

How much use has the chain and cassette had I wonder ?

 

[ufkacbln]

Is the chain slack?


Totally unhelpful, but could not resist

 

[ufkacbln]

More helpful (I hope)

Is it a stiff link?

Move the pedals backwards and when it skips watch the rear mech, a stiff link will be obvious and always occur at tee same point in chain travel

Also occurring more frequently on a smaller rear cog can be a pointer