Driveshaft Problems

well i been lazy here lately but here is my problem.

I got my driveshaft cut and re-welded back on we took 3 3/4" out of the back end behind the weight, i go to bolt it up and it like wobbles i took it to a shop they said since he cut and re welded it thats my vibration cause its off by 4 thousandths but yet when i had it on it would wobble/ vibrate up by the yolk, im guessing my u joint is shot to hell so i went and got a new is this the problem?

like were he welded it its right on that back weight could it possibly thru it out of balance and if i get it balance with the new u joint and it being off by 4 thousandths what this fix my problem

WHEN IT GOT CUT & RE WELDED THEY SHOULD HAVE REBALANCED IT FOR YOU..... THAT WOULD HAVE NEGAITED IT BEING OFF BY 4 THOU. IF THE U-JOINT HAS A GREASE FITTING MAKE SURE YOU GREASE IT ON A REG. BASIS LIKE WHEN YOU CHANGE YOUR OIL....

check and make sure the driveshaft is not too far out. if it's pulled out too much, the yoke has hardly anything to grab onto which will cause wobbling if it's near the edge of the spline. the spline is only so long.

why'd you have to shorten it that much? i calculated 1 1/4inches on mine when i move my drivetrain up.

lol when i ordered it from a guy like 46 miles from me i said is it this length so it will fit and was like ya sure u joints are great, i get it put the yolk on the saft and its hanging over 3 3/4" my guess is it came off same year as my truck but a long bed and the guy wanted to make some money.