Unless they're brand new gears, I hope you checked the tooth contact pattern before removing them from the original housing they were running in. Once a wear pattern is established, any other adjustment, including setting the backlash to specification will set up a howl that would make a timber wolf jealous. Most service manuals have a section on what to do to establish a proper running fit on new gears which is far too complex to address in a chat room post.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!