Originally Posted by
Ronno6
Well..................the short cage derailleur is good for 31 total teeth takeup.
The OP's requires one that will handle 34t.
Looks like the original medium cage derailleur needs to be replaced with same.
I haven't done the tooth calculations, but I'm damn sure that with a compact up front and a max 30T at the back, you can get away with the short cage. This is certainly true of my RD-5701 105 rear derailleur. Pretty sure you only need the medium cage if you're running a triple or want to go up to 32T max.