Gear Shimming Tutorial - YouTube Bevel Gear Shimming Revisited - YouTube
do it like this! it should end up sounding like this:
shimming it spur first ends up whiny/chirpy and overall just bad.
also ALL gearboxes are different. because somebody used .5 here and .3 there doesn't mean yours will be the same! my old gearbox needed 2mm of shims on each gear! x.x