I'm down to the last item on the to-do lists on my truck and it's a VIBRATION issue. Ive read through all the other vibration related threads and gone through a decent amount of diagnosis but haven't found the cause yet.

Vibration is at 75-85 mph
Vibration is present if I run it up to 85 and drop into neutral
Vibration is a little stronger on decel and I can mitigation it slightly with a smidge of positive throttle
Vibration is heard as much as felt.. it's a harmonic that hums like I have 2 wheels on the rumble strip of the edge of the highway
Front shaft was replaced with new.. no change
Had a shop reseal the tcase and no mention of output shaft slop.
Same shop checked all 4 wheels for play indicating hub or bearing issues
Tires recently replaced and balanced twice
Rotoflex checked and while not new appeared to be crack free
Alignment done with new tires

Not sure what to check next. I know the problem can be solved and is probably something simple but I need some ideas

 

 

Vibration doesn't appear to be in the front end as there is no wobble or vibration in the steering wheel.

 

Recently replaced complete brake system with new rotors
Tcase resealed last week and fluid filled

 

Has anyone ever had a parking brake drum cause anything like this?

 

 

 

That's a pretty high speed vibration, for sure. Seems weird that it comes on at only 75 mph, or above. My first thoughts would be tires at those speeds, but you've address those. So, I'd check the front u-joint on the rear shaft (it doesn't have to have sloppiness necessarily, it can be dry inside and binding) and look for signs of the balance weight being gone off the shaft (usually looks like two/three dimples where it was once spot welded on).

It seems like it is hitting it's "sweet-spot" for creating the vibration at a certain speed. Usually, again, usually...transfer cases, rear ends, wheel hubs and such come on slowly and gain vibration with speed...not all at once.

Driveshaft balance or binding can be more like you are describing, all at once.

​​​​​​​ Brian.

 

Yeah something is hitting a resonance. I'm thinking of having the rear tires pulled off the rims and checking for a bent rim. Maybe a lateral bend wouldn't be noticed until it hit the perfect speed?

I equate the effect as similar to a cell phone sitting on a table with the ringer off and just the vibrate function on. You can feel it and hear it

 

Stock hurricane wheels no spacers