Upgraded tranny from a 4L60E to a FLT 4L80E-5 and shopping for new/shorter drive shaft. Any recommendations as to reputable brands? Lightweight ones available/advisable?
Also
Acknowledging that it's dumb...having said that, when I hit 115mph there's a vibration that feels like it's coming from the axles, possibly driveshaft but could be wrong and then it stops at 125mph. Truck runs smooth again all the way to 140mph+. Rear is a stock 3.73 I believe. I know these trucks weren't meant to drive that fast but any ideas on what it is and how to fix it? Don't want to blow a shaft or axle on freeway going 150mph...I love this forum too much to not participate!! Lol

 

It's most likely the balance of the shaft. They weren't made to be run to that speed. At the very least, get the balance checked, and make sure it's a high-speed balance. I just ordered a shaft from Denny's Driveshaft, they ALL come with a high-speed balance. Supposedly...there's only a 5 pound difference between steel vs aluminum, I went with a steel shaft with 1350 universals on both ends.

 

i would guess the driveshaft is causing your vibration, although its weird that it stops at 125, i would think it should get worse. But the stock driveshaft isn't balanced well enough for those speeds. I get alot of vibration at about 80 with my gear ratio and am shopping for a new shaft as well.

Oh and for the 4l80e, you don't need to have a shorter shaft, just a new yoke.

 

Thanks for the tips, I'm gonna look into my drive shaft and see what I can do about it. Be nice if I didn't have to replace it at all!