New answers tagged adjustment
I don't think so, as long as you have correct cable housing and ferrules where you need them, there's no problem having multiple barrel adjusters. If you know how to use them then there's no downside to having three in my opinion. Try it and let us know!
It sounds like what is suggested by Robin -- when the chain is on the extreme cog on the rear it "kisses" the adjacent chainring on the front and begins to shift rings. But there is not enough chain pressure to make the shift complete so the chain slips back to the ring you were on. Sometimes this is unavoidable for certain front/rear combos, but sometimes ...
Does the bike have multiple chainrings? Make sure you aren't cross-shifting- that is, shifting into a gear that is too high/low for the chainring that the chain is sitting on. This can cause a problem like you've described- chain rubbing on front derailleur and constantly attempting to shift to put the chain into a more linear position.
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