rear drive shaft (3 Viewers)

[4x4veteran]

I have vibration that gets pretty noticeable around 60mph.
It feels like it is in the back.
Steering is solid and no vibs in steering wheel.
Had this before I put new tires on and balanced.
I checked the drive shaft and found about twenty thousands run out on the barrel and the yoke is so close to zero the indicator barely moves.
Got some noticeable backlash in the third so am looking into a rebuild.
Last time I did anything there was in 84.
Haven't checked for crooked axles or bent rims yet but just eye balling they look straight.
My question is would twenty thousands be enough to feel at speed?
I am looking for some place close to check balance.

 

[Sky King]

Vibration through the seat usually says back of the truck, replace the u joints and get the shaft balanced. While universal joints will still take grease bearing wear can be to the extent of causing vibration before a failure. Getting that done if nothing else will eliminate the driveshaft as a suspect. My two cents.

 

[4x4veteran]

Pulled the drive shaft cleaned and installed new U joints and still the same vibration.
Took the shaft to one place and not to go into it just say he was an idiot and pissed me off so am looking for another driveshaft place to try.
Weird story about U-joints.
Back in the mid 60's my first car was a 60 chevy wagon that when I took off it would give a slight shimmy and then smooth out as I drove.
I drove that car like that for a couple of weeks before I did some inspecting.
I was in the navy so it was a while before found/made time.
Upon inspection I found the caps that were held to the yoke by U-bolts were completely gone and just hanging in the U-bolts.
There was a lot of wear on the metal.
I guess the joint would slip down when I stopped then center it's self when I got moving.

 

[1911]

The working angles of the u-joints of both ends of the driveshaft need to be as close as possible to equal (though opposite). When you lift the truck, you compromise this geometry. You can correct it with shims between the spring pack and the axle.

Driveline/Propshaft 101 - https://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml#Measurements