I currently have a 7 speed bicycle, and recently changed my rear derailleur to a Shimano RD TX55 Tourney TX for a 6/7 speed compatibility. My shifter is Shimano Rapidfire for 7-speed.
The current problem that I have is that when I shift into the 6th, 5th, 4th, 3rd, and the 1st sprocket it becomes unstable. The RD is not properly aligned with the gears. The 7th sprocket does not have any problems. The 2nd sprocket on the other hand, I have to shift the shifter from 2 then change it to 3 only then it becomes stable in the 2nd sprocket.
Upon observation, I suspect that the RD is more towards for a 6-speed sprocket due to their alignment on the sprockets.
Is this true or is there some way to adjust the RD to fit the 7-speed sprocket?
Additional information: 1. The cable is tight, not slacking. 2. Barrel adjuster is 0, at its initial position.