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Thanks for replying, I really appreciate it. I shouldn't let it bug me as much, but I struggle with not being able to do things.... and this is properly beating me.
cheap plastic thumbies were notorious for being awfully stiff at the top push.
That's good to know.
Does the penultimate ferrule sit in the braze on, or is the ferrule too big and so is sitting outside and on top of it so to speak?
It sits outside. One of these:
...when it stepped to sit inside sort of like these:
(I know that there are also tonnes of different stepped ferrules - I guess a trip to my new LBC)if the L screw is set too far it will make the final push to get in to the largest sprocket even more difficult.
I will double check that. It's good to know.
certain is that the mech hanger isn't bent.
Pretty sure. But I've read this regularly from reading around so I will double check once the bike is back. I don't think it is though because it shifted fine when the DT shifters were on the DT, and other than the problems listed it was alright with the DT-thumbie conversion.
I will have a think about a 7 speed conversion. But the original plan was to change the handle bars and shifters so it could be used for commuting purposes. Then if she liked the bike (which she does) spend a bit of money making it "nicer" in the Spring/Summer next year. In which case cold setting the frame and making it an 8 or 9 speed seems more sensible from a compatibilty POV (ie use some of my parts bin).
hugo7-
Aye, that's understandable, I'd want to do the same and cold-setting to 135mm shouldn't be difficult when you come to do it.
With that in mind I'd probably go through it in this order:
Double check the hanger.
Get a stepped ferrule, without it sitting securely you'll always have subpar shifting.
Check the limit screws.Let us know how you get on.
±ln(x)
There could be a couple of things leaving you with problems. Firstly is that that the indexed shifter has a very slightly different pull ratio to that which is required by the mech which is why you're only experiencing some of the difficulties at the top and bottom end of the cassette. It's been a while since I've worked in a bike shop but cheap plastic thumbies were notorious for being awfully stiff at the top push.
Without seeing the cable outer length it's difficult to say for certain if it is long enough but if it makes one smooth curve from one end to the other and sits neatly in the boss/adjuster at each end then it's probably fine.
Does the penultimate ferrule sit in the braze on, or is the ferrule too big and so is sitting outside and on top of it so to speak? - This would have a significant impact on shifting accuracy.
I'm sure you've got it covered but the H/L screws should only just engage enough to prevent over-shift into the frame/spokes, if the L screw is set too far it will make the final push to get in to the largest sprocket even more difficult.
If you exhaust these possibilities or just don't care you could indeed swap to a 7 speed screw on block and get a matching 7 speed shifter and mech which would definitely all work together so any problem would be with cabling.
Oh one other thing that you could check just to be certain is that the mech hanger isn't bent.