I've searched the forums but have not been able to find any help so I'm starting yet another thread from a new guy....

I have a 2001 Supercrew 4x4 with the 5.4 and a 9.75" rear axle. The truck has 190k miles on it. For a while now it's been making a cycling wooshing / rubbing / churning sound from the rear end (not a howl or squeal). Sounds like tire noise but changing the tires does not help. It doesn't matter if the truck is accelerating, decelerating, in gear or neutral, but it varies with the speed of the truck. The noise is there when going straight or turning right, but seems to diminish when turning left. I changed the U-Joint at the diff and I've replaced both axle bearings and seals. Then filled it all back up with Royal Purple. The sound may have gotten quieter but is still present. This may just be something I have to learn to live with but I would really like to know what the problem is and how serious it is.
Also, when I pulled the rear rotors off the parking brakes looked good, no grooves or broken parts. But maybe it is a brake or rotor problem.
Any help would be welcomed... Thanks

 

go to ford and ask for friction modifier. put that in the rear end.

 

Added the Motorcraft friction modifier yesterday and have driven about 100 miles but still no difference. Could this be pinion bearing noise? If so how much can I continue to drive before I have a catastrophic failure?

 

100% sure its coming from the rearend? when you go to the right does it get louder and then when you go to the left you said its almost gone? sounds like wheel bearing in the front.

 

i had a similar problem on my mustang a few years ago, and i pray for your sake its not the same thing but there is only one way to tell. remove the rear diff cover and inspect those gears i had chiped a tooth off of the ring and the pinion,and the constant grinding made an awful noise it constant low tone growl, before you remove the diff cover just open the filler plug and stick your finger in there and see what the metal content is, the more metal oz the worse off your are. i think thats what it is but i hope im wrong.

 

i just read the left to right thing i agree if it changes with turns it could very well be a wheel bearing

 

Finally took it to the shop and was told it needs a pinion bearing. May just try and find a used rearend, might sell it, not sure yet. Should have alot of miles left in the rear, just might have to live with the noise for a while.