Ok i need some help. I had some horrible vibrations that led me to replacing the center bearing on my drive-shaft. While it was off i had them replace the u joints as-well. Now when when i first start of i get a horrible shudder when accelerating from about 5mph-10mph and never reappears until i have to start and start again. It never did this before.

Here is what i probably did wrong, at least i think. Under advisement from a mechanic "friend" we didn't mark anything when we took the shaft off. We also didn't have the drive shaft balanced. He said that you dont need to worry on these trucks about it going on the same way it came off. I need to fix this! I am afraid that i am going to screw up the truck more if i keep driving.

If this truck isnt running i am not making money.

Thanks in advance for any help.

Also we tried spinning the rear section 180 degrees

Its a 2004 Chevy 2500hd 4x2 Reg Cab Long bed

you dont have to have the driveshaft balanced on the truck. but it maybe out of balance like a weight came off or the carrier bearing might have gotten something under it when you where putting it back together.

And it would shake like that when starting off? I would think that it would show up at higher speeds. I am admittedly car stupid. I decided to do this myself cause it is so easy to remove.

most times it does get worse as the speed gets worse but if its not that bad or a small problem it maybe the only time it vibrates enough to notice. you could put the rear up on good sturdy stands and have someone drive it at that speed and see if you can see anything vibrating. just be careful there is stuff spinning and if not good stands can tip over and truck will take off with you under it.

the drivelines need to be in phase , did they mark the drive lines so they went back together as they came off (splinged ) ujoint caps lineded up . but would show up at higher speeds not at lower speed

Yes they marked them. My partner had it at the mechanic today. Looks like a mount is bad. I think he said it was the trans mount.