Need to know if I have a medium or long cage 10 speed rear mech.
It’s an SLX RD-M675 – 95mm between jockey wheel centres.
Recently went 1×10 and bought a Sunrace 11-40 cassette but it doesn’t sit on the 40T.
Guy in a bike shop said I don’t need a longer B screw, but change to a GS (I think) mech.
Loads of people on the Cannondale Trigger thread have done this but I can’t recall this being mentioned.
Does this sound right? Loathe to buy a new mech on top of all the other bits I’ve changed…please help!

Both medium and long cage work with 11-42 only short cage doesn’t. So with a 11-40 you shouldn’t really be having any issues.

GS is medium cage and they don’t do short cage slx, so I can’t see someone recommending you go for a medium over a long cage?

But any slx should be enough for 40t really.