Hi all, need a bit of help adjusting a rear derailleur, followed parktools and etc to fix it.. Index is spot on (i think ) .. Shifting is smooth and quiet from small to bigger cog.. Its when going back down to smallest cog where total chaos is.. Chain jumping or not move at all with just one click of the shifter..

Double post sorry, dont know how to delete

i think you have 2 options here,

1) maybe the indexing isnt really spot on and you need to adjust the cable tension so there is less cable tension. try moving the barrel adjuster a bit and seeing if you can find a place where the mech moves both ways happily

2) the indexing is good, but for some reason the spring in the mech isn’t pulling the cable properly. This could be due to worn outer \ frayed inner, the inner cable just needing a clean and lube, inner cable is kinked somewhere inside the outer casing, or maybe the cable routing is causing a problem and some of the bends in the outer cable are a bit sharp.

or maybe your mech just got old and saggy and it isn’t doing its job any more