I have a gearbox mainshaft that may be bent. How can I check that? I don't have a lathe handy to chuck it in (did you see what I did there?). But I do have a dial gauge, so that's a start. It wobbles when installed in the gearbox. But that's in neutral when I hold the shaft to stop it turning but turn the rear wheel so the main driving/output gear through which it passes, turns.