Originally Posted by
Collin2424
Hi,
I read that a derailleur really isn't speed specific - it travels the same amount of distance no matter what. So my question is, what creates these indexes? Is it a function solely of the shifter, or is there something else I'm missing? It would seem like I could get any newer derailleur and it should work fine with my 7 speed cassette. Is this true?
It's not just the cable pull. The rear derailleur's actuation (or throw) ratio is also critical to the distance traveled per click. Fortunately all Shimano SIS or STI RD's have the same throw ratio with the exception of pre-9-speed Dura-Ace
Another consideration is the width of the cage compared to the overall width of your chain. In your case I would try to find a derailleur closer to your 7-speed generation. Not sure but I'm thinking that a 10-speed RD may have a narrower cage. You could run an 8-speed chain with a slightly narrower overall width.
I agree with JanMM. Check to see if the problem is excess friction in the cable housing.
Al