I pick up my c4 transmission next week from being re-built to handle the new 347 that's going into my 67 convertible.I'mtold I'll have approx 450HP.I have the stock 8 inch rear end. Besides doing a 9 inch rear end total swap, what should I need to have done to the driveshaft...? Yokes and U joints? Balancing? What does it mean to balance the driveshaft? Do I need to get these things done right away, or can I drive the new motor and rebuilt trans and break them in with the existing 8 inch and driveshaft etc as is? I plan on breaking in the engine and tranny and not beating on it during this process...I'm tired of spending money. Project went WAAAAY overboard.

 

You don't have to change a thing for now. Just drive it and enjoy but just don't push it too hard for a few thousand miles.

 

that's what I wanna hear, thanks! makes sense...

 

If you have any vibrations coming from the undercarriage or out of the back then you need to have the drive shaft balanced, and possibly the U joints inspected, but Idoubt you will have any of those problems.

 

I would drive what you have, then when you go for the 9" I would purchase a 3rd member with a 1350 series yoke, and have a new driveshaft made up with 1350 series u-joints front and rear. Doing it one piece at a time would not be very cost effective.