Occasional chan slip in high gears

[Andy in Germany]

I'm getting occasional chain slip when I pedal hard in the smaller rear gears. It's occasional and intermittent, so I'm not sure whether it's that my indexing is inaccurate or has some other cause. What symptoms should I look for to determine what the problem is?

 

[SydZ]

Worn spockets?

How much do you ride in those gears? With less teeth smaller sprockets work harder and wear out quicker.

 

[Brandane]

If it doesn't happen in lower gears then possibly bent derailleur hanger?
Or sticking gear cable which would give same symptoms as indexing being out. Worse in higher gears as it is under less tension hence more likely to stick.

 

[Blue Hills]

Can be a tricky one as it's rather hard to look down and behind when riding along the road (unless you want to bang your head on a kerb like I once stupidly did as a kid)
And of course this sort of problem very often will refuse to show itself on a workstand.
You need to establish if the chain is changing cogs. If it is relatively frequent I'd do some test rides on a clean quiet stretch of road - check which rear cog you are in and then check again after any apparent slip.
I try to avoid using an 11T rear cog or even 12T unless pushed - really really late for something or trying to catch a group ahead - they are frowned on by many as they wear very quickly and do bad things to the chain running - I often click to it then back again and just spin/increase my cadence.

 

[roubaixtuesday]

As others have said, it's hard to diagnose between poor indexing causing gears to change between cogs unexpectedly, and wear causing slippage when reliably in a gear. That it's only on smaller gears suggests it *could* be a bent hanger rather than indexing. A fraying cable is also a likely candidate.

I would probably do something like:

(1) Measure chain wear. Replace chain if worn (cheap and easy). If that makes it worse rather than better, then it's a good sign the cassette is worn. Replace that.
(2) If chain not measurably worn, re-index on the stand following Park tool guidance.
(3) If still problematic, replace cable (cheap and easy) - outers too next (generally a PITA)
(4) Get LBS to check hanger alignment (or just replace)

Good luck.

 

[mustang1]

I read that as "occasional chin slap".

 

[Sharky]

Check for any stiff links on the chain and also check the quicklink is still in place correctly.

 

[Paulus]

As above advice, also,
Check the cleanliness of the chain and cassette to see if there is any build up of crud in between the sprockets.

 

[Andy in Germany]

Thanks for the suggestions: I'll start looking into those. IN the meantime the chain seems to have started something new: after riding in heavy rain last week, and despite a fresh oiling of the chain, it feels like it's full of gravel in the mid gears and to a lesser extent in the bottom gear. Top gear is quite smooth though.
Does this extra information suggest anything or narrow down the options? I have a sneaking suspicion that it's related the the jockey wheels, but that's only conjecture based on an impression that the chain isn't running true in the jockey wheels sometimes, and the feeling could be caused by the chain running over the outer frame of the rear mech slightly. This is backed up, possibly by the feeling that in top gear, when the outer frame is most likely to be pulled away from the chain, it feels smooth, but as @Blue Hills says, when riding it isn't easy to make a detailed inspection of these areas.

 

[Blue Hills]

Thanks for the suggestions: I'll start looking into those. IN the meantime the chain seems to have started something new: after riding in heavy rain last week, and despite a fresh oiling of the chain, it feels like it's full of gravel in the mid gears and to a lesser extent in the bottom gear. Top gear is quite smooth though.
Does this extra information suggest anything or narrow down the options? I have a sneaking suspicion that it's related the the jockey wheels, but that's only conjecture based on an impression that the chain isn't running true in the jockey wheels sometimes, and the feeling could be caused by the chain running over the outer frame of the rear mech slightly. This is backed up, possibly by the feeling that in top gear, when the outer frame is most likely to be pulled away from the chain, it feels smooth, but as @Blue Hills says, when riding it isn't easy to make a detailed inspection of these areas.

why do you suspect the jockey wheels? Are they very worn/gone pointy?
Even if pointy/very worn I'm not sure that would cause a drive slip - though would change them anyway if they are shot.

 

[Blue Hills]

By the by, are you sure it's the rear?
I had slippage issues once - thought it was the rear.
Some careful checking, noting which cogs I was in front and rear and then riding up a slope, revealed that it was actually the middle ring of my front triple - changed the middle ring and all was sorted - very odd as it was a new chainset - maybe a manufacturing fault. As I recall it wasn't changing front rings, just slipping on the same middle ring.

(what we folks really need of course is specially trained small dogs to run behind the bike and deliver a tick-box report - business opportunity there)

 

[Andy in Germany]

More weirdness: today there was no roughness, just an occasional feeling like a vibration.

In other news I've finally met the bike wrench at work, and we got on like a house on fire, so I can use the bike stand at work to check the gears if they play up again...

 

[Punkawallah]

Wah. This is better that Coronation Street :-)

Vibration sounds a worry if you're doing an 18k commute (iirc). The rear derailleur could be faulty/misaligned. If the jockey wheels are not aligned with the gear the chain will tend to 'chatter'.

My 'go to' would be to swap out parts with spares until you hit the right one. Don't know if this is an option for you? I have a spare Shimano SIS I'd be happy to send.