The gap can't be zero for two reasons.pdlpsher1 wrote: ↑Thu May 02, 2019 1:12 amCal,
I know your preference towards having a small gap between the top pulley to the largest cog. Next time when you have a Shadow-based Di2 bike in your hands, adjust the B screw for a small gap and try shifting from the second largest cog to the largest cog, and see if you hear a clunk on a small percentage of shifts. I tried to reduce the pulley wheel gap on my bike but I get the 'clunk' on perhaps 20% of the shifts from the second largest to the largest cog. Increasing the gap solves the problem. I don't think the noise is an indication of a bad or missed shift. But the noise just doesn't sound good when all other cogs shift without any noise. Perahaps this is a Shadow Di2 specific problem. I now have Di2 on my tandem as well and it does the same thing. I'm just curious if you can duplicate the problem on another Di2 bike you have access to.
1. When the chain derails it's riding the cog and eating into the distance.
2. The derailleur (and guide pulley) moves in a line over the cogs, not sideways then height adjusts.
So when in 2nd gear and starting a downshift you already at this point need the complete minimum cog-riding pulley distance for the 1st gear which you don't have yet.
So adjust until the noise disappears and keep testing shifting 2nd to 1st.
When the pulley is offset from cage pivot point it complicates things if you're on 2x becauese the pulley distance changes depending on which chainring you are in. Offset is usually but not always found on 1x derailleurs.