Rear derailleur trying to pull back too far in lowest 2 gears

[Fifelad]

The chain and sprockets are not excessively worn, it happens more under extreme tension on the chain ie going up a steep hill, my immediate thought was B screw adjustment. On a long ride I adjusted in small increments as I rode so the jockey wheel was closer to the sprocket, in the position so the derailleur cage doesn’t move back as far, it’s still trying to do it, the B screw is about on its limit at that extreme. The only other thing I could think of was perhaps the chain could mabye do with a link out it to increase tension when in the lowest 2 gears ? Opinions please

 

[Peter Salt]

Not sure I understand completely, but it sounds like a chain length issue. How many links you have? What's your largest chainring, cassette sprocket and chainstay length (centre of BB to rear axle)?

 

[Fifelad]

Should of mabye been a bit clearer the chain was trying to skip off the jockey wheels in the lowest two gears, so the deralliuer was appearing to try to “pull back” . I’ve just been fettling with it again and fingers crossed it is running a bit more smoothly albeit in the stand, with tension on it yet to be tested again. The chain is has the normal amount of links it always has so really shouldn’t need a link out it.

 

[Paulus]

Is the chain and rear mech all clean and moving freely across the range?
If the jockey wheels are far enough from the sprockets not to catch on them I doubt that's the problem.
It could simply be an adjustment issue.

 

[midliferider]

The chain and sprockets are not excessively worn, it happens more under extreme tension on the chain ie going up a steep hill, my immediate thought was B screw adjustment. On a long ride I adjusted in small increments as I rode so the jockey wheel was closer to the sprocket, in the position so the derailleur cage doesn’t move back as far, it’s still trying to do it, the B screw is about on its limit at that extreme. The only other thing I could think of was perhaps the chain could mabye do with a link out it to increase tension when in the lowest 2 gears ? Opinions please

Let me understand the issue here.
When you want to engage the largest cog on the rear cassette, it will not move.
At that point, Jockey wheel is touching the cassette.
Is that correct?

 

[Gunk]

Have you recently changed the cassette?

 

[Fifelad]

Everything was running sweet, indexing well etc. It was only when in the two lowest gears under tension, the chain is not completely engaged on the jockey wheel. I’m going to try it again in a couple of days as I’ve adjusted the b screw again and it is smoother, but that’s on the stand. Thanks for the input all

 

[Fifelad]

Is the chain and rear mech all clean and moving freely across the range?
If the jockey wheels are far enough from the sprockets not to catch on them I doubt that's the problem.
It could simply be an adjustment issue.

Yes everything clean and moving freely across the whole range I think it’s a case of adjustment
Yes every

 

[Erasmus]

I've had issues with something as daft as attaching the cable to the wrong side of derailleur bolt, slightly altering the pull. This caused perfect changes over the first 7-8 gears from where I'd set it up (usualy from smallest sprocket), and then played up over biggest sprockets. If I tweaked it to be fine in biggest sprockets, it would then go out once down to the the little ones.

Good luck in sorting this out, John.

 

[Fifelad]

Cheers 😂

 

[Fifelad]

Well the plot thickens… I had everything spot on in the stand, I then put on a new chain and cassette and the problem is now worse. Over the lowest three gears, the chain is trying to pull off the bottom jockey wheel and although there has been a slight difference after b screw adjustment it’s not fixed the issue. I’ve thrown in the towel and it will be a visit to LBS on Tuesday 🤔