Used to run a 3700 car in modified production that had a 57 to 64 Pontiac 9.3 inch rear axle. It would crack teeth on the pinion gears. Took a new set to a heat treat place and had them soften the gears by three or four numbers and didn't have the problem with the gears cracking any more. Cheap solution. Cost twenty bucks to have them done back in the late 60's early 70's. Probably be about 75 of todays dollars.