Jockey Wheel Screw

Secteur

regarding the screw on the rear derailleur - not the H / L limiting screws, but the other one that adjusts the distance between the jockey wheel and the cassette...

...no matter how far I turn it in either extreme, it seems to make absolutely no difference to the distance.

I cant figure out why?!

it's a full 105 groupset.

crankycrank

It's called the B-tension screw. I've run into this before and sometimes it's just the combo of where the mech hanger has been placed or it can also be your chain is too long or short resulting in no visible adjustment. Also try adjusting the screw and then shift through the gears once or twice while pedaling to see if the adjustment has changed.