Alright, here's the deal. I've replaced all 4 u-joints, front and aft. Both axles had 1 dried up seized OEM joint. No problem.
But I still have this annoying vibration between 75-80mph. Also, when letting off the gas during the vibration, I hear a droning noise for like 1-2 seconds.
Well I figured maybe I unknowingly crushed some of the needle bearings on one of the u-joints when installing. So i take out both shafts, and check the joints. All 4 move around nice and quietly. All 4 seals look to be intact and fine.
Well I believe I've narrowed the problem down to the front driveline, b/c the vibration is mostly felt in the steering wheel, and the slow 4WD disengage problem is back again. Also, I put it in 4WD to see how that affected the problem (I know, 80mph in 4WD = no good). Anyway, truck runs smooth as glass in 4WD.
So I decide to leave the front shaft off and see if the vibration is still there, or goes away with the shaft. Interestingly enough, the problem remains with or without the front driveshaft installed. Not good!!
My question to you guys is, how much rotational play to you have in the front shaft when twisting it by hand (while in PARK)? My front seems to move a lot, probably like 1/2 - 3/4 inch. Seems odd, especially since the is no play what-so-ever in the rear shaft.
Is yours the same way?
Is my front diff. shot?