Just wanted to add. That I had a very noticable vibration after installing my ford 9". And a few other drive train components leaf springs, bushings, shocks, drive shaft, traction bars, tailshaft bushing and u joints. After a long process, I finally eliminated the vibration by adding 4 degree pinion angle shims. I angled the pinion upward. I suppose the low pinion on the 9" was causing excessive drive shaft angle and causing the driveshaft to vibrate.