Help Needed Vibration (rubbing) at 75mph exactly!

[Deadman514]

I'm getting a sound from under the truck at exactly 75 on my speedo (not sure what actual speed is because of larger tires). I can drive without looking at my speed and when the noise starts -the needle is at 75. Goes away at 80.
Just started happening two weeks ago. Been trying to track it down since. Sounds like the tires rubbing -bumps make it worse but there's no evidence of rubbing (the dirt in the wheel wells not rubbed off).

Please help!!!

 

[JLDickmon]

get under there (truck parked, of course) and shake the driveshaft in the joints & yokes....

 

[Deadman514]

Thanks. Not it though. Jacked up the front end...no play in the pretty new ball joints or unit bearings. No play in the driveshafts. Vibration happens in 2 or 4wd. Hubs locked or unlocked. Nothing I can see is rubbing although the sound is like a fender rubbing the lugs on the tires.

 

[Deadman514]

(truck parked, of course)

Bout to ignore this part to figure it out though!!!

 

[Deadman514]

Would have thought at least the smart a##es would have chimed in by now?!?!?!

 

[BIG JOE]

Tranny tailshaft splines need re-greased ??

If so.. use the Marine grade stuff (blue).. lasts longer.

 

[Zookie400]

are your front hubs locked when it happens?

 

[Deadman514]

Locked, unlocked. In 4wd, out of 4wd. In 4wd with hubs unlocked.......

 

[Dogman]

I would lean to the driveshaft support bearing. But I have seen the rear seal on tranny do so werd stuf too. Find a good TRUCK lift and get all four tires off of the ground, and run it up to speed and have someone look for the sound. That all the dealers will do. Just be safe doing it.

 

[Deadman514]

How much play am I supposed to have in that thing? one guy tells me it's supposed to be a bit loose and another tells me he can hang off his without it moving...