According to the chassis manual, there is no torque spec. You tighten it a little at a time until you can detect no endplay. Then you have to check pinion preload drag with a pound-inch torque wrench. Pinion preload drag is 20-25 lb. in. for new bearings and 10-15 lb. in. for reused bearings. There is a special tool for holding the companion flange, while tightening the pinion nut.
