I just finished setting up an old steel mountain bike for touring and it came out great except on the first ride everytime I'd get out of the saddle and put a little power to it, the axle would move foward in the drive side horizontal dropout. The tire even started hitting on the chainstay and it moved no matter how tight the skewer.
I looked at the dropout carefully and the inside face was wallowed out some (concave) so I figured perhaps the axle nut wasn't seating well against it. I put some brass on the face and filed it smooth and flat thinking perhaps the brass would give it something to bite into. Tried it out and it still moves.
Next step was to merely center punch the dropout surface a bit to rough it up and that helped quite a bit but I'm worried that isn't a good permanent fix.
Any thoughts/ideas on fixing this? Perhaps inletting the dropout surface a bit to capture the axle?
Mountain bike hub, 9 cogs, derailleur hanger is sandwiched against the dropout by the skewer. Have to spring the rear open just slightly to install the wheel. All looks straight.