I've got a 12 bolt Moser and I never checked the backlash and I'm trying to track down a vibration. When I turn the axles it seems very tight, is this normal? Also as the topic says can backlash being too tight cause a nasty vibration?

 

Yes, little or no backlash can cause vibrations, although usually it's accompanied by some sort or whining or scraping noise. It can make it hard to turn or even bind up the gears when you're trying to do it by hand. You'll have to check though to make sure.