another ? about my 1st 741 build

First, that wrench isnt what you should be using. Because it requires more torque to initiate rotation than continue it. You need a dial type wrench like the above. Mine's an older Snap On but same same. Second, you dont torque the nut to 15-20lbs. that's your problem. You have to torque it to spec which is 240 pound FEET. Then you have to rotatie it using the right dial type wrench and if it's les than 15 INCH pounds, you need to remove pinion shims. If it's more than 15 INCH pounds, you need to remove shims from the pinion. You dont torque the pinion nut to 20 inch pounds. You torque it to 240 pound feet to checkthe preload. It's a balancing act to get the pinion depth and preload right. but you'll find that if you do, the backlash will be a peice of cake to get right and the pattern will come right in for you. BTW, I use good bearings with the IDs enlarged as "checking bearings" for the various pinion types. It goes a lot faster that way...