Just had my 1998 F150 in the shop to replace the rear differential fluid. The truck has 138K miles and I knew it was overdue, but was not having any problems. The shop found the rear pinion seal was leaking and the fluid was a little low. I said go ahead and replace the seal. Three days later I am going down the interstate and the rear end begins to roar. Took it to another location of the same shop and after road test they say sounds like the pinion bearings are suddenly going bad. Took it to Ford and they said the other shop screwed up the original repair by not properly tightening the pinion. Can someone explain how this happens? I have to go back to talk to the first shop next week.

 

To replace the pinion seal you must remove the driveshaft then the flange that hold the driveshaft to the rear end. The flange is held in by a nut, called a flange nut.. that nut is too be torqued to crush a sleeve to set the pinion bearings into there races the seal is between the flange and the bearings they remove that nut and flange to remove that seal.. during reinstallation if that flange nut is NOT properly installed (tightened) correctly it won't take long to burn up the pinion bearing..

hope that explains it for u..

 

The ford repair guy said it could be caused by not tightening it enough or tightening it too much. Is this correct?

 

yes!!! Too tight or to loose will cause the same bad results....

 

Is it a certain ft lbs of torque, or do you just have to adjust it until you think it is not too tight and not too loose? The tech at the second shop said something about using 90 ft lbs of torque. BTW thanks for all the info.

 

In my show we use a weighted bar after torqing the nut some were around 90ft wesecure the bar to the flange and whatch the bar free fall to watch how much resistance is on the bearings it is almost a touch or experience feel ..

 

Do you remove the wheels and take a pinion shaft preload reading? What about counting the threads between the end of the nut and the end of the piston shaft before removing the pinion nut?

 

u should yes... and yes preload is the term that is used when tighting the nut..
I never have counted threads. anytime i have rebuilt a rearend i always replace the flange nut because the used nylon lock in the nut may not told the flange tight and may loosen after time..

good luck..

 

i had a similar problem with my seal took it to the dealership, they rplaced it and apparently screwed up the install. i started feeling a thump on acceleration didnt think much of it and over time it apparently screwed up my pinion bearing. expensive mess