Overhauling my 83' Raleigh I found a spacer in the rear dropout on just one side. This prevented the wheel from sliding all the way back into the dropout. I've taken the spacer out and the bike seems to work fine and also its easier to center the wheel within the seat stays because I just pull it back all the way into both dropouts. Using just the one spacer I need to pull back on that one side then carefully try to match the other side while tightening the skewer. Can anyone tell me why I need this spacer? Should there be one on each side? And which side should it go on the drive side or opposite? THanks-Joe