High pitch whine above 40mph...

[TexAndy]

I think I figured out the problem with mine.

Took it over to a diesel mechanic and he listened to it. Said it was road noise from the tires. Because the rears are fairly worn. And worn unevenly. I drove it some more and concurred.



Looked the truck over a bit more carefully and it turns out the middle axle is off center about 1.5 inches.

I think I could back the truck up onto a ramp to get the middle axle off the ground, but once it's there, I have no idea how I'm going to move the axle over. Maybe drive another truck alongside and use a bottle jack to press between them? These rockwells are HEAVY.

 

[paulfarber]

Deflate the tires to about 15psi (the pressure for use on sand) and see if the noise changes.

I kinda doubt that road noise is going to make a high pitched whine... maybe a dull static sound.. but not high pitched.

Tires should be within a a quarter inch of each other in diameter, otherwise they will scuff.

Changing the fluids should not have done anything for the noise.. wear is wear... no fluid can replace lost metal on a shaft or bearing.

 

[M35Brown]

It's just gear whine, wear may cause more whine, but it's just gear whine.
All 18 wheeler type trucks have this whine, some more than others due to type of transmission, and amount of insolation in floor and firewall.