Chain Jumping

[JtB]

My chain started jumping on Monday and sure enough when I measured the chain it was quite stretched. I then replaced the chain and it is still jumping. I took my rear sprocket to my LBS and they said it was NOT worn, but the problem might be a stiff link where I joined the new chain. Sure enough this link was stiff and so I managed to work it lose, but the chain is still jumping. I'm going to take my front sprockets to my LBS this evening, but to be honest, they don't look worn either.

Anyone got any ideas where the problem might lie? I'm wondering whether there might be a problem with the rear derailer chain tensioner. I have noticed for quite a while that when I peddle backwards the chain tends to shift from the smaller to the larger rear sprockets (in fact, this even happens occasionally while free wheeling). By the way, I set the length of the new chain by counting the number of links and using the same number as the old chain.

One last observation, the chain tends to jump on both front sprockets and the 2 smallest rear sprockets.

Any advise much appreciated.

Thanks,
Shaun.

 

[PpPete]

What state are your cables in? I've heard replacing gear cables can make a big difference - although I've never understood why. Maybe some more expert member can enlighten us?

 

[Mr Pig]

My bet is that both your cassette and front rings 'are' worn. If you've been riding with a worn chain I can't see how they could possibly not be.

 

[JtB]

I don't think there's a problem with my gear cables as the chain is not slipping 'off' the sprockets. Also, my bike has the old style of gear levers, so the rider can compensate for any cable stretch by positioning the levers accordingly.

Just before I stopped using my bike many years ago I know I replaced the rear wheel and think I also replaced the block. If I did replace the block, that would explain why the sprockets are un-worn. But there is considerable resistance when I 'back peddle' which has set me wondering whether there's a problem with the mechanism inside the block. Maybe its ratchet (not the chain) that's slipping. Is this something that can happen with old blocks?

 

[goo_mason]

My chain regularly jumps from the middle to the big chainring as I change to the smallest rear sprockets. Not sure why - the derailleur cage isn't anywhere near the chain so it's not being pushed up.

My only thought is that the chain's maybe a bit loose and hitting any kind of bump as I'm shifting might cause the chain to bounce up and catch onto the big ring. I've just ordered a new chain as the old one's showing stretch according to the chain checker, so perhaps I'll make it a link shorter than the current one and see how that goes.

 

[JtB]

A new block has fixed the problem and it now runs better than when it was new (30 years ago).

 

[e-rider]

Definitley the cassette if you've been riding with a worn chain. Bad advice from the LBS as it's almost impossible to see the kind of wear to the cogs but it's enough to make the chain jump - they should know this! Lesson: replace the chain frequently and then you will not need to replace the cassette too much - I get through a chain every 18 months and a cassette every 6 years (Shimano) That'a a ratio of 4:1

 

[goo_mason]

My chain regularly jumps from the middle to the big chainring as I change to the smallest rear sprockets. Not sure why - the derailleur cage isn't anywhere near the chain so it's not being pushed up.

My only thought is that the chain's maybe a bit loose and hitting any kind of bump as I'm shifting might cause the chain to bounce up and catch onto the big ring. I've just ordered a new chain as the old one's showing stretch according to the chain checker, so perhaps I'll make it a link shorter than the current one and see how that goes.

Nope - new chain on, definitely not loose and 'jumping' on a bump as it's doing it when the bikes on the workstand. It's spooky - I just can't see what's making it jump from the middle to the big ring ! Anyone got any ideas ?

 

[fossyant]

Chain line......

My MTB will drop from outer to middle if I back pedal on either the top sprocket or the second (not that I use the top sprocket) and that's on a 7 speed rear !

 

[Mr Pig]

Anyone got any ideas ?

Without seeing the bike it's pretty hard to have any ideas. Could the alignment be out? Maybe a new bottom bracket fitted that's not the right one, too narrow, and that's throwing off the chain line? I'm just guessing.

 

[Ashtrayhead]

What state are your cables in? I've heard replacing gear cables can make a big difference - although I've never understood why. Maybe some more expert member can enlighten us?

My gears were jumping last week and eventually stopped when the cable snapped! So it could be a frayed cable or one that's had it's time!

 

[JtB]

Chain line......

My MTB will drop from outer to middle if I back pedal on either the top sprocket or the second (not that I use the top sprocket) and that's on a 7 speed rear !

My old Carlton doesn't have a Cassette Cluster, but a 'Traditional' Freewheel Block instead. Before I changed the Block there was considerable resistance when I back peddled and my chain moved up the sprockets (from the outer to the inner). As soon as I replaced the Block, that fixed the problem. My wife's bike also has the same problem so I shall replacing the Block on that too.