Originally Posted by
Awesomeguy
It is partly the principle, if they can prove it is similar component then...
As
travbikeman eluded to earlier, Shimano have at least three 9-speed Shadow-style derailleurs: the M4000 (Alivio), the M3000 (Acera), and the M2000 (Altus). Alivio has recently been re-numbered to M3100, so maybe you can count that as four 9-speed derailleurs now...and this is just in their MTB range. They probably have another one or two in their road range. They're all functionally the same (at least the ones in the mountain range) but will differ in small details like styling touches, small differences in materials, etc.
Originally Posted by
Awesomeguy
but also, i do notice as i had created a thread below, that certain gears, when in the big chain ring in the front, don't allow for the rear deraileur to operate as smoothly. but i 've never had shifting problems, I hate to go through the hassle, but it might be worth it to address my concerns described below.
Bigger chain ring on 2x - Bike Forums
Because the shifting is smooth in both front chain rings, I'd say it's not likely anything the derailleur itself is doing (or not doing). It's possible the derailleur hanger, which is the shiny chrome-looking piece bolted to the frame to which your derailleur is mounted, could be bent. This might allow the right chain angle while in the small ring, but a non-optimal angle while in the large ring. It's hard to say without seeing/hearing/feeling it for ourselves. It's almost certainly not related to the derailleur being an Acera vs. an Alivio, though.