Just changeing to a spool has nothing to do with how the gears mesh and they should run just as quiet as before.
I agree with Ed completley on this. Typically the if the pinion depth is correct and drive side patter is good the coast side should be also.
We typically set the backlash between .006" and .008" I don't recommend any more than .010" worse case but only on a street aplication. if you have to go more than that to get your pattern you've got pinion depth issues. So back to the drawing board. Backlash can have an adverse effect on tooth contact just as pinion depth does and if a guy isn't using the correct tools and measureing equipment to check backlash, shim thickness and set bearing preload it won't be right.
Good Luck :wink: