This is my first post, but I've been reading this site now for the last month (great info). I bought a 95 V6 4wd automatic about a month ago for a good price, but it had a bad vibration. And after reading this site, it appears I'm not alone. The vibration started at about 50mph and got REAL bad about 70mph. I read every thread on this site and others that could cause vibration. It seemed that many were caused by tire-wheel balance issues (lug-centric). Well, I took off my wheel and found that it's hub-centric, so all the issues with improper wheel balancing do not apply. It appears the lug-centric issue started with 3rd gen 1996 and on. Still I'm thinking to get the wheels balanced, but I'm not convinced that this was the problem. Other info pointed to the driveshaft, u-joints, slip yoke out of phase, etc. After reading in my FSM, it says a potential cause of vibration is a stuck slip yoke. So, I removed the rear driveshaft and wow was surprised. The slip-yoke was definitely stuck, and the front u-joint was very rough and jerky; the rear u-joint was not as bad but still rough. Also to my surprise was the staked nut on the companion flange on the rearend of trans was LOOSE. I have read that this is a cause of vibration too. Now what caused what to go bad - I don't know. But I bought 2 new Toyota u-joints, and replaced them. But I had to hammer apart the slip-yoke. The guy who owned this truck before me must have used the wrong grease, because once I had it apart, the spline was covered in this hard, plastic-like grease residue that was baked on. I then cleaned it up and greased it real good. I then tightened the nut on the companion flange, restaked it, and reassymbled the driveshaft with new u-joints installed. I said a long prayer and then conducted my test drive, and hallelujah, the vibration was gone.

Now as I said before I don't know what caused what to go bad, but I know I had 3 things contributing to the vibration - loose nut on the companion flange, bad u-joints, and stuck slip-yoke. Thanks to everyone who educated me with all the info I gathered from this site regarding this problem.

One last thing I'm still puzzeled over though is the loose nut on the companion flange. This nut was finger loose and the companion flange would wiggle. The nut was properly staked. So my question is - How did it get loose? Very mysterious, but thanks again to all - my vibration is fixed - hallelujah!