High Speed Vibration

Well guys I need some help.

Here is the whole back story.

A few years back when I grenaded my 4l60e I went ahead and replaced my u-joints at the advice of my father even though the stock ones were fine. After replacing the stock u-joints with Acdelco joints I had a vibration past 80mph. One day I got cocky and pushed through the vibration and that led to the rear u-joint coming apart at 100+ not cool. Replaced with spicer joints still had vibration.

Fast forward to when I trashed my 10-bolt. I had lived with the vibration for over a year and just never whet over 80mph. When I rebuilt the rear end I did everything. Lets start up front I have a stock 4.8l bolted to a circle d stall to a FLT lvl 4 4l60e. I had a local shop build a 4inch steel shaft with 1350 spicer joints for me to replace the suspected bad stock shaft. The rear end is just your normal 10-bolt build up: Detroit true trac, usa standard 4.56 gear set, yukon axles, yukon rebuild kit and a ta girdle, The pinion angle is spot on and I have caltracs to help keep it that way.

After the 500 mile break in I was so excited that the vibration would be gone. NOPE anything over 95mph feels like something in the driveline is coming apart. Took the shaft back to the local shop watched them re-balance and it was fine. Took all the wheels in and had them re-balanced and they all checked out. I am at a loss here. I'm suspecting trans issues now but I'm not sure that makes much sense. Sorry for the lengthy post. and thanks for any advice

Damm man that sucks, and scary when it comes to the driveline. You got a shaft loop? I'd install one if I were u.no wonder how a aluminum 5" shaft would do on your setup

No, no hoop yet. Planning on building one though. I don't drive the truck much but, would still like to not see it go up in flames.

Is the truck lowered? Sounds like a driveshaft angle problem, your front and rear yokes should be parallel to minimize vibrations.

Truck is on 2in shackles only. Angles are near equal but opposite. I might try dropping the trans some though.

Chased the same problem in my truck for a year .... and I work in a drive line shop for a living lol! I finally swapped complete rear ends. When I sat my old rear end on the ground I noticed it was banana shaped so I'm assuming that's where my vibration was at. Another thing to look for would be a bent axle. Also check the yolk on the rear end , it has 2 tits on the outside of it that hold the caps in place. Sometimes those tits get wear on them and allow a slight side to side movement of the joint. You should have to lightly tap the u joint into the rear yolk. Also check your shaft and make sure all the snap rings are in their grooves. Sometimes it looks like they're in but won't be . Take a hammer and flat head screwdriver and tap the snap ring into the groove. Also if you have the shaft out see if the u joints are moving freely or if they're kind of tight. If they are tight tap the yolk of the driveshaft a few times with a hammer and it will loosen them up . Any other questions feel free to text or call 601-580-4373.

Well this points me towards a bent housing. I just don't know what I would have done to bend it. Guess its time to find a 14bolt or dana 60. Wish I would have kept the 60 I had out of my Ford. All of this just makes me so mad because the truck was unbelievably smooth at high speeds before I blew up the trans.

I bent mine doing doughnuts in the yard, broke an axle and bent another ha ha . Is the truck 4wd or 2? Also one piece shaft or 2?

Guess I should have mentioned that, it is a rcsb 2wd one piece driveshaft.

That's what mine is, if it was 4wd or a 2 piece shaft I was gonna tell ya a few other things to check.