78 Chevy 1/2 ton still has shudder, any help??

Trailblazer, That sounds like a driveshaft that is bent, running off-center, or out of balance. If you had the driveshaft balanced earlier, it is possible that now, one of the balance-weights has been lost. Another idea: the U-joint caps may not be driven in equally now (missing any C-clips?), which would let the driveshaft run off-center. Badly worn splines could also let the driveshaft run out of true. That full-time Tcase would make it possible for the front driveshaft to be the problem, if the front driveshaft is always turning as fast as the rear driveshaft. Any good driveline shop can check if each driveshaft is running true (not bent or off-center at the splines or U-joints), and balance it, if necessary. That is specialized work, but it is not too expensive. Get some bids, first, to avoid surprises. Run the truck on a frame lift, and when the speedometer reads 35, any driveshaft problem should be easy to locate. Cheers, Red

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Trailblazer wrote:

If it's an automatic:

Look if any weights broke off of the flexplate?

Refinish King

PS A cracked or worn at the center flexplate can also do that!

someone mentioned me have the flexplate checked, so i went back to the guys who did it and they said it was fine, it did it before and after the rebuild so I figure they would have caught it. I'm guessing the only thing left it could be is the driveshaft like red mentioned?

thanks for your help, i think you posted about the flexplate and why i went back to the guys to have it checked.

TB