Cool, got news today my driveshaft was fine, in my case it looks now that the slip yoke was to long banging the back of the rearend and causing the bushing to bind up and it spun that bushing to where no tranny fluid would lube it.....Raising the tranny 1" and checking pinion angle tomorrow

 

How long is your slip yoke? Mine measures 5.5 inches on the barrel.

 

i duno for sure but i know its long as hell, ill have to double check it when i get it back....

 

Who built that trans? Sounds like they did their job!

Definitely sounds like there is an issue there. These units do have some bushing issues as well as end play issues in my opinion. What you found will probably help however I would still be concerned with the internal bushings. Have to see what happens with what you have planned and go from there. Vince

 

I installed the new tailshaft housing with new bushing. Its better than it was, but the slip yoke still has some play when pushed up and down by hand. Its certainly tighter. At speed its also better, but I still have a slight vibration at ~80 and a more violent vibration above 100. Something still isn't right.
The slip yoke I have is used and I'm suspecting that. Maybe the splines don't have a tight fit? I don't know what the slip yoke originally came from, it is used and I believe it came from one of GM's failed aluminum driveshafts.
Anyone have anymore ideas??? Comments?

 

If you put the slip yoke on can you twist it and see if the splines have any slack in them? To double check drive shaft length i suggest pulling your tail housing, put driveshaft back on w/ full weight on tires, your slip yoke should be about an inch away from bottoming out on the trans, this will allow for your rearend to tourque and not bottom out on the back of the trans, also id highly suggest checking your pinion angle......If you used your original trans crossmember like i did you will want to put a 1" shim underneath the tailhousing then set your pinion angle

 

this might help you too, if you look under your truck and your trans is pointing down and your rearend is pointing down this is a sign pinion angle is off, mine was like that..... any time you run a negative pinion angle like that you will get alot of vibrations

 

I'll try all of those things. Thanks for all the ideas.
I used the stock crossmember and the trans tail housing does point down, so to counter that my rearend pinion points up. I used a machinists level to measure the tailhousing angle and then set the pinion angle to an equal opposing angle. Then I welded the spring perches in place.

 

more than likely our problem is the trans pointing so far down, most practical application for a high horsepower or tourqe application you want your trans up around level and rearend 2 degrees down from what i gather

 

I have looked into everything suggested by all and still no fix. However, I think I have a solution to my problem. My driveshaft is 3.5 inch steel and around 60 inches long. I called a driveshaft shop and explained my problem. They said it sounds like a text book, "critical speed" problem. He said at speed its too long and heavy and begins whip like a jump rope. It would explain my tailshaft bushing being out of tolerance if that shaft is so violently shaking the truck. The solution is a 4 inch aluminum shaft, which being lighter will spin faster before reaching crital speed. The driveline shop I spoke with was Denny's Driveshafts and the guy took the time to listen to my problem and was very helpful. I will certainly be ordering from them soon. He told me if I hold the truck at speed with the current shaft, I risk the shaft coming appart, so I won't be at the track again until this is resolved.
Scott