[Azathoth]

Their is a mathematical way of shimming gears that I have used.

You will need a set of digital calipers and a way to measure the left side to right side spae between your gearbox shell bearings.

It's VERY straight forward and anyone with a high school diploma can do it.

If your gears are making a lot of noise it's very likely that your bevel gear is not properly shimmed for your pinion. Generally I start with a 0.20 shim on the spur gear, then start shimming. I have found from experience that 0.20 is near the ideal clearance between gears. Take a shim and put it onto the spur and rotate the gears while putting pressure on the axles of all the gears. The shim should clear without problems each other gear.