AKlowriderZ71

iTrader: (22)

Ok, so my truck shuts down at 98 MPH, but it gets there quick. I'm looking into HPTuners or something similar, so I can change that, and other things. Here's my question. At what speed is my rear driveline going to become unsafe? It is the one piece rear driveline, made of aluminum, probably 5 or 6 inch diameter, for the extended cab. I remember reading an article several years ago talking about the driveline's critical speed, and the yoke coming apart, or coming out of the t-case, or something like that. I've been searching, and can't find it.

95ImpSS

iTrader: (2)

Dunno, but I've taken my Yukon up to ~116mph the day my wife passed out at work, and I had to drive 50 miles to get to her b/c she refused to take an ambulance to the ER. Yukon's driveline & suspension was as smooth as ever (mind you that's a lot of weight hauling *** along the interstate w/ 4L60E & 3.42s).

hmatiak

iTrader: (1)

Mine vibrated like hell above 90. It was the same setup you have. Ditched it for the 2 pc setup from an extended cab. Much better.

-Heath

AKlowriderZ71

iTrader: (22)

I don't have any driveline vibration, that's not what my concern is. I want to know what speed my stock driveline is safe to, in it's current configuration, without coming apart due to reaching it's critical speed.

AKlowriderZ71

iTrader: (22)

Bump, anybody??

PathfinderJr

iTrader: (6)

there's a mathematical way of determining at least an estimation of the speed before your driveshaft turns its self into a sine wave. Google it maybe. You have to know the material, wall size, tube diameter, and length I think.

And if that doesn't work, just search around here for all the threads about broken driveshafts, and don't go as fast as them haha.

agreif

iTrader: (4)

I would stick to the 98 limiter if you don't have a loop in there. Technically the shafts should be good up to 150+ with a perfect balance, but you aren't going to get a perfect balance with a factory shaft, they have no reason to spend the extra expense. In my mind it's really a gamble. If you take that gamble you could take your transmission with you....ask me how I know.

https://www.performancetrucks.net/fo...d.php?t=364990

PathfinderJr

iTrader: (6)

not to split a hair, but just in case others are reading this thread for info, a driveshaft isn't rated up to a certain mph. They are rated at how many revolutions they are safe to turn. Everybody is gonna see that critical speed at different speeds due to tire, gearing, and tranny differences.

On the '66 my dad and I just finished, a shop did offer us a 1-piece driveshaft, but being as how the truck is a long bed, the shaft was super long and had a critical speed of somewhere near 4k rpm. I don't know what speed that would have equated out to, but I felt way more comfortable going ahead and having a 2-piece unit built so it's more stable. Sure its a little more parasitic drivetrain loss, but throwing driveshafts isn't very fun.

agreif

iTrader: (4)

very true, I had a RPM which I converted to a MPH for my 3.42 gear ratio and 3rd gear ratio. Use the calc in thta referenced thread and you'll be able to get a critical rpm