Tabulator on Smith Corona Classic 12 is not working?

I have Smith Corona typewriter Classic 12 that I had polished up and refurbished. It was working until (I think) it fell off my desk. It seems now the Tabulator is not working to set tabs. There is a set button on the top to the left, tabulator in the middle, and clear button on the right. When I set it to a position for tabbing and then press the tab key, it either skips ahead a space or get to the position a space before, and then also doesn't stop at all. I tried clearing it after moving the moving piece to complete right and then hit clear. Still the problems persists. I looked at all the springs, the ones I could see at least, but everything looks intact. I don't know if its the teeth or soemthing else, but any help appreciated. thx.