Can't shift down from 50T with clutch on, but can shift down with clutch off, why?
I'm using sunrace 11-50 and XT RD-M8000 (SGS), finished setting up everything for absolutely perfect shifting, then realised the clutch was off. Turned it on, shifting is still excellent (but with the usual clutch effect) except it will not shift out of 50T. The shifter clicks, the RD stays put, same thing if I do multiple shifts down. I can however backpedal for a while after one downshift to drop the chain into the 42T, the RD then moves, after which I can pedal forward and carry on shifting down perfectly.
This is not a derailleur setup issue, not only have I got everything setup by the book, but I've played around with 4mm to 12mm gaps between the 50T and top pulley with B-screw with no luck.
My calculations (full formula including 2 links for derailleur, not rough estimate) showed that 113.4 (=114) links on the chain should be enough, I installed with 117 links initially, felt that was too much chain, removed 2 links and am using 115 now. Doubt it's chain length, can't see why everything would be fine with clutch off if it's chain length, but worth considering.
RD is just out of the box, so I doubt it's the Nm on the clutch, but going to check that out soon.
It's not a big issue, since there are only 2 to 5 (depending on conditions) places where I need/want the 50T and all of them are during the (mostly) climbing half of my local rides, so I can ride up with clutch off and ride down with it on.
Above all I'm curious why extra chain tension from clutch could cause this; even if the Clutch tension is too high and that is the reason, why would this happen? After all, it shifts even under quite a lot of load with clutch off (I avoid this bad shifting practice where possible, I was just testing!)