Joined: Feb 2012
Posts: 19,320
Likes: 5,428
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Have you tried to remove the wheel and feel how the axle spins in your fingers? Does the bike use a disk brake? If so then there can be disk/pad rub during the side to side shifts when pedaling, given the very tight clearances between pads and rotors.
First thing is to isolate the problem. Then the options and tools become known. Andy.