The driveshaft was not fine

Two weeks ago this journal recorded that the rear driveshaft slid back into the slip yoke by hand, that nothing was leaking, and that there was good reason to think nothing behind it needed replacing. It also said this: reason to think is not the same as knowing, splines can gall, and it goes in the column of things that look fine and get checked again. That hedge earned its place faster than expected.

The symptom came first, and it is the part worth writing down. With the replacement axle under the truck, the driveshaft would not mate to the pinion flange. It needed to telescope further into the slip yoke than it was willing to go - not by much, but the bolt holes would not line up and no amount of persuasion was going to close the gap. A driveshaft that will not reach is easy to blame on the axle sitting wrong, or on pinion angle, or on the wrong part. It was none of those.

Off the truck and in daylight on 4 October, the mouth of the female splined yoke is nicked and peened around the lip. The most likely explanation is that it ran partly engaged after the impact pushed it forward, and the burred lip is now binding on the shaft splines before the joint can collapse to the length it needs. The transfer case output splines look sound, which is the good news in this.

The fix went the way these things sometimes do, which is backwards. Ford sells the slip yoke on its own (ML3Z-4841-B, around $200), and the workshop manual is clear that U-joints get installed as complete kits only - so repairing the shaft on the truck means a yoke plus a U-joint kit plus pressing them in. A complete one-piece driveshaft, ML3Z-4602-AE, is $307.94. Adding a kit and the labor to the yoke costs more than the whole assembly, and the whole assembly arrives with new U-joints already in it.

So a complete shaft was ordered on 4 October from Stumpf Ford, with the rest of the axle parts. It is not here yet. The four flange bolts went on the order separately because the manual says to discard and replace them, and the transfer case fluid gets checked once it is all back together, since the yoke spent time out of the case.

The honest summary is that a part was cleared too early. The entry that cleared it said it might be wrong, which is worth something, but it still sat on this site for two weeks reading more reassuring than it should have - and it took the axle going back in to prove it.