Gear jumping problem

[BikeLB]

Hi everyone

Help! I have a Cube road bike that has Shimano Sora gears. I’m having a serious problem with it ‘jumping’ when running on the smallest gear at the rear. I’ll try to describe ‘jumping’; it’s not actually trying to climb onto the next gear but appears to be perhaps catching on the top of the teeth on the same gear it’s already on – if that makes sense. It gets worse if it’s under load but does it if I just crank the bike by hand on my turbo setup. When under load i.e. being ridden, the jump is a very noisy ‘clank’ noise. It’s not possible to ride in that gear.

I have tried adjusting the position of the jockey left or right using the adjuster screw and clearly the derailleur moves left or right as I adjust. However, that doesn’t seem to stop it jumping no matter where I put it. The hanger looks straight.

I checked to see if the chain has stretched and I think not. Compared to my other road bike (different gear) the chain does appear to be much easier to twist. (That is to say if I get hold of it between my fingers and rotate it along the chain length. I did this in the middle of the span to the front gear).

Any ideas? Is it adjustment (but I can’t see how it can be) or is it something else? Could it be the bush in the idler gear is worn? (It does wobble a bit more than my other bike). Or is the chain simple knackered?

I can’t possibly be the only person who has experienced this.

Any advice gratefully received.

Les

 

[Cycleops]

Problems like this are so difficult to diagnose at a distance. Could be any number of things. Don't think its cassette wear as that would manifest itself in the more used gears. Could be the chain if you done a good mileage on it but more likely to be adjustment of the cable.

Maybe try a new cable and adjust it from scratch. There are many YouTube videos, or drop it into your LBS.

 

[Ming the Merciless]

Stiff link or links?

 

[screenman]

Without a tool I do not think you can see if the March is aligned. How old is the chain? Smallest gear, do you mean large or small sprocket.

 

[raleighnut]

Sounds like a 'stiff link' to me too.

 

[mrandmrspoves]

If it were a stiff link I would expect similar in all gears (although amplified as you get into the higher gears because the chain would be on a tighter curve)
If only on one gear sprocket I would look closely at that sprocket for a bent or damaged tooth or trapped debris. Also try to work out how frequently the clatter occurs.....each wheel revolution or each chain revolution or constant.

 

[Levo-Lon]

As said sounds like a dodgy link or links.
Check the split link too

 

[Levo-Lon]

If it were a stiff link I would expect similar in all gears (although amplified as you get into the higher gears because the chain would be on a tighter curve)
If only on one gear sprocket I would look closely at that sprocket for a bent or damaged tooth or trapped debris. Also try to work out how frequently the clatter occurs.....each wheel revolution or each chain revolution or constant.

tends to show up more on the smallest cog due to extreme angle though you may have a point with damage and debris.

 

[mrandmrspoves]

tends to show up more on the smallest cog due to extreme angle though you may have a point with damage and debris.

Yes- higher gear ....tighter curve - that's what I wrote!

 

[Levo-Lon]

Yes- higher gear ....tighter curve - that's what I wrote!

You did, apologies

 

[gbb]

Sounds like chain stretch and it's skating...not meshing with the sprockets.
Measure chain, you need to do that really because it can be one of the most common causes of wear and problems.
If the chain has stretched that much that's it's skating over the sprocket, it's quite likely you'll need a new cassette as well.

 

[BikeLB]

Thanks so far guys. To clarify, it is the smallest gear at the rear. It does look a bit like stiff links but it happens a lot - as if there are more than one in the chain. I guess I'll have to take the chain off and go around it and see if any links are stiff. That would be odd though as while the mileage might be relatively high it's been used a lot indoors on a turbo rather than out in the dust and rain etc. Anyway, I'll have a look tomorrow as it's actually my partners bike and she's got the London Tri in two weeks! I may have to resort to buying a lot of new parts. Time will tell.

 

[Kajjal]

Thanks so far guys. To clarify, it is the smallest gear at the rear. It does look a bit like stiff links but it happens a lot - as if there are more than one in the chain. I guess I'll have to take the chain off and go around it and see if any links are stiff. That would be odd though as while the mileage might be relatively high it's been used a lot indoors on a turbo rather than out in the dust and rain etc. Anyway, I'll have a look tomorrow as it's actually my partners bike and she's got the London Tri in two weeks! I may have to resort to buying a lot of new parts. Time will tell.

That’s very unfortunate timing for you. Stiff links should show up with the chain on if you prop the bike up and turn the cranks backwards. Sometimes just oil and riding the bike can sort it. If it is high mileage you may end up needing a new chain and cassette. Have a look at what the rear mech / derailleur is up to as well.

 

[boydj]

Cable may be slightly too tight. Either screw in the cable adjuster at the mech or loosen the cable, make sure the mech is properly aligned on the small cog, using the adjustment screw if required, then re-tighten the cable.

 

[BikeLB]

UPDATE: SORTED!
I thought I'd return with an update in case it's of benefit anytime to someone else. I had a situation where the small gear jumped, much in the manner of a stiff link. But they are not stiff. I checked the chain stretch and wear and there is some but not really enough to be responsible. I adjusted the derailleur in all directions and checked the hanger is straight. All these things and no cure.

Anyway, despite keeping everything reasonably clean what I hadn't noticed was what I thought was just a bit of black greasy muck between the gears on the cassette. Specifically between the bottom two gears. There is very little clearance on the links when the chain runs around the smallest gear and it had in fact been reduced to less than nothing by a bit of cotton thread or similar wrapped around that diameter. It was preventing the slack lower portion of the chain from running around correctly and in fact lifting the links up a bit. It was enough to cause havoc. Having dug it out with a small sharp screwdriver it's now all back to normal. Yay!

Thinking about it I should have realised it was something sudden as it happened while my partner was out riding and was ok one minute and no so good the next. Picking up something can occur at any time so worth keeping that part clear and if it all goes wrong, checking that first.

I'm more than pleased to have sorted this without spending out for a change!