Migrating vibration.

[the_novice]

Wasn't sure where to post this as I don't know where the vibration is coming from.
1985 ranger 2.8 5speed 4x4
235/75r15 wrangler territory tires.

I have a high frequency vibration in the floor of my truck. It starts on the drivers side at about 70 km/h then starts to fade at about 85 km/h. Then at 100km/h it starts on the passenger floor boards. Only the driver OR the passenger can feel it at any given time. Also sounds almost like driving on the rumble strip only higher frequency. I've confirmed that both hubs are unlocked by lifting and spinning the tires. The vibration is related to wheel speed not engine speed and is constant through shifts from 3rd to 4th and fifth. And the truck does not shake hop or dodge on the highway. Also wheel bearings are good.

Sorry if my post is a little scatter brained.
Any ideas would be appreciated. Thanks.
Taylor.

 

[alwaysFlOoReD]

Check your u-joints.
Swap tires front to back.
Have you done work to the rear end gears? Or work anywhere else?

Richard

 

[the_novice]

U joints are good. And no work done to the rear end. Started after I buried the truck in soft wet top soil. On my way back to town I figured it was just mud packed in the rims but no such luck. I did notice the rear drive shaft may be one spline out on the slip yoke. The vibration didn't start right after I put the drive shaft back in though. I'll try fixing the driveshaft tomorrow. Then I'll try swapping the tires. Thanks for the ideas.