9 Speed chain jumping epidemic

[Andy in Germany]

On a number of bikes in the last few months we have chains mysteriously jumping while riding. We can't find where the chain could be snagging, in fact we can't tell where the problem may be; the chain just jumps suddenly. for no apparent reason.

Changing components doesn't help; the chain keeps jumping no matter if we add a new chain, rear mech, crankset, cassette...

The only solution we've found so far is to pull it apart and rebuild as an 8 speed bike, then the problem vanishes. It's getting to the point where we don't even bother trying, just throw out the 9 speed system on the first jump because it saves time.

Does anyone else have this issue? How have you diagnosed/dealt with it?

 

[All uphill]

When you say jumping do you mean jumping off the chain wheel? Skipping gears?

I'm interested because I've recently put a new chain and cassette on a 9 speed bike and made gear changing worse! I'll be double-checking the hangar alignment later today and changing the cable to see if that helps.

 

[T4tomo]

poltergeist

 

[Andy in Germany]

When you say jumping do you mean jumping off the chain wheel? Skipping gears?

I'm interested because I've recently put a new chain and cassette on a 9 speed bike and made gear changing worse! I'll be double-checking the hangar alignment later today and changing the cable to see if that helps.

When riding/ turning the chain intermittentrly jumps forwards, causing the rear mech to pull against the spring to take in the tension and jump back when the chain goes slack again. In the current case this seems to have no bearing on the gear, position of the chain et c.

 

[T4tomo]

chain suck on a worn chain ring?

 

[bikingdad90]

Incorrectly adjusted b screw so too little tension allowing it to jump?

 

[HobbesOnTour]

On a number of bikes in the last few months we have chains mysteriously jumping while riding.

Is it the one rider?
Is it in the same geographical place?
Can you recreate it on the stand?

If it was one bike I wouldn't be too fazed with trying to work it out..... but several bikes? That would bug me.

Is there any commonality between the components you are removing?
I'm presuming they are different brands and models of bike?

And why does it disappear with an 8 speed setup?
What exactly do you change? It must involve changing shifters and cassette, at least?

What about the place where the bikes are brought in? Any change in personnel or systems down there?

Maybe it's my cynical mind but what happens to the 9 speed stuff when you remove it?

 

[All uphill]

When riding/ turning the chain intermittentrly jumps forwards, causing the rear mech to pull against the spring to take in the tension and jump back when the chain goes slack again. In the current case this seems to have no bearing on the gear, position of the chain et c.

That sounds remarkably like the problem I am struggling with.

I'm using chains branded as KMC. They were cheap and I'm wondering if they are knock-off ones. If I find anything I'll report back.

 

[Ming the Merciless]

Do you mean the rear derailleur swing arm (holding jockey wheels) gets pulled forward then swings back?

 

[Andy in Germany]

Is it the one rider?
Is it in the same geographical place?
Can you recreate it on the stand?

If it was one bike I wouldn't be too fazed with trying to work it out..... but several bikes? That would bug me.

Is there any commonality between the components you are removing?
I'm presuming they are different brands and models of bike?

And why does it disappear with an 8 speed setup?
What exactly do you change? It must involve changing shifters and cassette, at least?

What about the place where the bikes are brought in? Any change in personnel or systems down there?

Maybe it's my cynical mind but what happens to the 9 speed stuff when you remove it?

Different riders, apparently different place on the ring/chain.
Different places.
It isn't all 9 speed bikes but all the bikes with this problem are nine speeds.
It's odd that it vanishes when we go to 8 speeds, but not when we change the 9 speed components.
We've changed every component as far as I can tell; we went through them one a a time to try and isolate the problem.
Anything we usually remove is so worn it could be used as a ninja death star.

 

[Andy in Germany]

Do you mean the rear derailleur swing arm (holding jockey wheels) gets pulled forward then swings back?

Yes, this seems to happen more often than not, but even that isn't 100%. I'm also not sure why the chain tension increases.

 

[Andy in Germany]

That sounds remarkably like the problem I am struggling with.

I'm using chains branded as KMC. They were cheap and I'm wondering if they are knock-off ones. If I find anything I'll report back.

I'm using XLC chains, but I've used them successfully on other 9 speed bikes and generally use them on 8 speed systems too.

 

[Ming the Merciless]

Yes, this seems to happen more often than not, but even that isn't 100%. I'm also not sure why the chain tension increases.

Does sound very much like chain suck on front chain rings

View: https://youtu.be/C_7ivRiR9tc

 

[Andy in Germany]

Does sound very much like chain suck on front chain rings

View: https://youtu.be/C_7ivRiR9tc

It does, but when I turn the pedals slowly in the stand, looking directly at the chainwheel, I can't see any evidence of chain suck: it's a very frustrating experience.

I'll look specifically for that tomorrow and see if I can see anything.

I'm beginning to think @T4tomo is right: it's poltergeists.

 

[fritz katzenjammer]

Is it the correct chain for a nine speed system and is it on backwards, it must go on writing side out.

Its amazing how many times I’ve seen freshly serviced bikes come through the shop with similar problems and its the wrong chain or its on backwards.