Originally Posted by
72andsunny
Not sure we’re talking about the same thing. The gear is unusable because the jockey wheel is hitting the large cog. See video above somewhere. When riding in that gear, it makes the entire bike vibrate.
Ahaa. Well, that's simple then: your cassette is outside the limits of your RD. You either need a different RD or a Wolftooth or similar extender. B screw has nothing to do with it. You're outside your RD cog size limit. I've been assuming that this is a stock tandem. Apparently not.