Drive Shaft Requirements

Question for you guys. At what point is a factory drive shaft not strong enough. We found that the drive shaft in the cuda was bent due to the motor / tranny grenading. So... we took a new shaft the shop to have it shortened and the shop told us we needed to go aftermarket. The car is 3300 and should run mid 9s. 727 Auto with a dana 60 rear. What do you think?

I bent/twisted 2 stock shafts running mid 10s at 3700 lbs. You definitely need a good one at your level. I'm currently running a 3" dia. steel "thickwall" shaft made by my local HD truck shop. So far it's help up running 8.90s at 3900 lbs., but I honestly wouldn't be surprised if it failed on me. Everyone else at these speeds is running 3.5" dia. shafts.

3.5" is much better than a simple comparison of diameters suggests.
With the same wall thickness (I used 1/8" for this test) 3.5" is 62% stiffer than 3.0", and only weighs 17% more.

Wow... big difference in just an 1/8" on strength

You are past due for a better than OE drive shaft.

That seems to be the general feeling. Looks like it's time for an upgrade....

14+ years on the same 3 1/2" chrome moly shaft and just had new 1350 spicer u-joints installed and a re-balance..........over kill maybe..........

How long is the shaft and how many RPM?
My Cuda has the motor moved way back and it has a Powerglide, the drive shaft is small diameter and short. The former owner had a Blown alcohol B1 motor in it with 5:57 gears and 16x33x15 inch slicks
Once I found out what ratio those gears actually where, I was told that it had either 5:13 or 5:38 in it, I swapped those gears out for a set of stock Dana Corp 4:56 gears
I think it crosses the finish line in the 1/4 mile now right at 7000 RPM.

Mark Williams has an excellent calculator for D/S size vs. speed here: http://www.markwilliams.com/driveshafttech.aspx

Hey Cab, the drive shaft is 45" long and I figure the new motor will 6500 - 6800. The old motor turned 7200. The dana is a 4:88 gear

The Mark Williams graph is definitely handy.

I ended up contact the shop and am going with the heavier shaft with heavier yoke also

I would agree with whats here for sure. IMO a 3" shaft will work fine but 3.5" aint gonna hurt. Also lots of material options out there. Most local shops can handle making something for your power level easy enough. If you want to aftermarket Mark Williams is the best IMO

Do the math on the drive shaft RPM by figuring in the converter slip and then go from there. Add room for more RPM in the future

thanks for the advice guys