I needed a clutch derailleur to go 1x for my Trance X 29er build. I raided my derailleur spare parts bin and came up with this franken-derailleur:
- XTR M980 link, top knuckle and parallelogram;
- XT clutch mechanism from XT Shadow Plus rear derailleur (not sure on exact model);
- short cage from 10 speed Zee rear derailleur.
Total weight: 229g.
I needed a rear derailleur in a hurry and this certainly beat running down to the LBS.
There is, however, another perfectly sensible reason (at least for the Zee bit of this derailleur) and that is: you can't buy a lightweight Shimano clutch rear derailleur with a short cage. The only short cage options are Zee and Saint (both about 270g).
By why run a short cage?
Well, you want to run the shortest cage you can get away with. That way the derailleur is tucked up as much as possible. You also get to run a shorter chain.
But can I use a big cluster?
Surprisingly yes. The short cage is good for 29t capacity. That means on a 1x system you can use up to an 11-40T cassette. That's what I've got on in the picture.