700r4 swap driveshaft question...

[JJSmitches]

I am told I will need to have my driveshaft shortened by 3 inches, but I am wondering if it wouldnt be worth it to simply buy a new driveshaft...possibly one made out of aluminum.

[Fuelie Fan]

there would be pretty much no benefit to buying a new steel shaft instead of shortening your current shaft, unless the driveshaft shop tells you otherwise (like if they inform you that shaft is twisted or bent).

Obviously aluminum has weight savings potential, but I'm not sure how much since driveshafts are somewhat cyclicly loaded, which means fatigue. Fatigue is not AL's strongpoint, which means they have to be over-built. Remember, you're accelerating the shaft in rotation, so what's important is not only it's weight, but where that weight is placed. If it weights half as much but is twice the radius, you haven't gained anything (actually, since I is proportional to m*r^2, you'd have actaully increased inertia)! So, for a street car, I don't think it's worth it unless you want something else to polish. Just my opinion. If one were to measure an AL and stock driveshaft, one could compute exactly what you would be saving in weight and inertia. I'm curious, do AL driveshafts come with any sort of quality gaurantee?