The Stovebolt Site Forums The Shop Area Engine Shop Two piece driveshaft to One piece

6' is getting pretty long. Below is the recommended tube thickness at various lengths. I would would strongly recommend 2 drive shafts however, if you have a slip joint at the transmission, it is a problem. You really should have a U joint at the back of the transmission and a slip joint between the center bearing and the third member. If you go the 1 piece route, I would certainly put a guard around the drive shaft. A 6 ft drive shaft can really be wicked.
The general length limitations are as follows:
* Installed length u-joint center to u-joint center.
ACS = Adjusted Critical Speed
Suggested factors for Adjusted Critical Speed:
Safety Factor = 0.75
Correction Factor
Outboard Slip = 0.92
Inboard Slip = 0.75

TC = Theoretical Critical
CF = Correction Factor
SF = Safety Factor
Tube O.D. Maximum Length *
3.0 in. 60 in.
3.5 in. 65 in.
4.0 in. 70 in.
4.2 in. 72 in.
4.3 in. 73 in.
4.5 in. 75 in.
5.0 in. 80 in