Vibration....
 

Hey guys......84 SR5 Extra cab, 22R, 5 Speed. ...Have a strange issue........you know how when you ride over a road with the washboard surface, and you get a vibration that is constant............well, I have the same issue at 20 mph and again at about 40 - 45 mph. It is the washboard feeling but not near as bad as a road vibration but same feeling. I have tried different gears, engine speeds, etc. Even out of gear I get the vibration. Any ideas???

Hard to say, it could be a lot of different things. You say the vibration is there even in neutral, but didn't say if the truck is moving or not when you tried it in neutral, so that means it could also be in the driveline (dented or bent driveshaft, worn or broken u-joints, worn out carrier bearing, worn bearings in rear, worn rear gears with too much play, etc.) My '78 used to do this too & it turned out to be the the trans input shaft bearing; an easy fix when the trans was out of the truck. Could also be other bearings in the trans. Could also be worn or broken clutch components, worn clutch plate slipping at different speeds (don't laugh, I've seen it happen like this), worn throwout bearing, warped flywheel (kinda rare), or any combination of these.

Only way to know is literally going over it all front to rear. Nothing beats a really good inspection.

The vibration is always when moving. About 20 and 40-45 mph. I checked the u joints, and center support bearing. All seems good., I do not feel the vibration in the steering or in the drive train. Leaning toward tires as they were just replaced a couple of months ago.

If this turns out to be a missing or lost wheel weight consider yourself very lucky.

I'm gonna say: Ujoints or slip joint or both.

No vibes / changes in vibes when you switch from accel to decel or vice versa? If you do: then rear diff pinion bearings going out.
The T-Case output bearing takes a ton of abuse, most probably not it.

Tires: I know that MTs from BF Goodrich make a noise after 20K, sounds like wheel bearings @ 30mph

I have been driving another vehicle for a bit so haven't checked out anything else on the Toy. Having a real cold snap in NC now, so it may be a bit linger. Thanks for all the information so far.