While looking for a bad u-joint, I discovered that my pinion shaft in my 9 inch rear moves! Now, the pinion is tight in the rear. I can't make it rattle or budge in any direction, but if I turn it, I notice that the u-joint flange moves very slightly before the shaft does!! The pinion shaft nut is fully torqued (I checked). Very weird. I can only assume (before I tear it down) that the pinion splines are worn, but that seems very rare to me. I post what I find after the teardown, but does anyone have any ideas?? Polkat

 

Ford pinion yokes period are soft cast iron, they all will wear and get loose. It is a very common problem. New ones out of the box fit sloppy most of the time also, nature of the beast.