I've followed the Park Tools Rear Derailleur adjustment video exactly, step by step, because my bike was jumping gears after I reinstalled the rear wheel after changing the tube.
The bike however won't shift in the rear from the 2nd biggest to 1st biggest cog. All other gears shift smoothly with seemingly no issues. I have tightened the L screw all the way, then did quarter counter-clockwise turns, trying to shift each time, and the chain at first would not shift at all, but after the L-screw was more loose the chain would momentarily shift to the big cog then return to the previous gear. I repeated this process until the L-screw was completely loosened and it did not appear to help. I also tried working the L-screw in combination with small clockwise turns of the barrel adjuster which seems to have made no difference.
This is a brand new bike which I’ve owned less than a week. Is there a way to fix this?
