vibration at 70 mph, non tire related..
 

It is weird, i tried using two different sets of tires, it only happens at 70-75 mph, nothing less, and it will clear up at 80 mph somewhat.

i do have an aluminum d/s, the u-joints are'nt old, i feel it through the shifter, but also kinda coming from the rear? only thing i havent tried was rotating the d/s 180, but thats what im fixing to do, im stumped guys:confused:

Well, if it does it at a set speed, rather than a set rpm, then it's something between the tranny output shaft and the rear wheels. If you're sure it's not the wheels, that leaves the rear end and the driveshaft. It's a lot easier to turn the driveshaft than it is to tear apart the rear end, so that would be my next step. If turning the driveshaft makes no difference at all, the rear end becomes your number one suspect.

Good luck!

Take care,
~Chris

hey pkrwd, i looked closer, and found something i overlooked before, the rear u-joint has a broken/cracked rubber seal on one of the caps, i guess that could be ready to fail!, i also noticed the vibration getting worse, although it's not old, i bought it from o-reilly months ago, i got a new one, high performance from autozone.
after thinking about it, i remember wheel hopping at the track real bad, probaly broke it, and on top of that launching at 5 k on slicks probaly shortens the life of u-joints.
My compressor is toast so i cant use my impact on the d/s bolts, DOHT! but tommorrow im gonna put the $%^$# to em with a breaker bar, i have them loctited on:o
thanx pkr

Rotate driveshaft 180*

I would replace the u-joints, for obvious reasons, and see if the vibe goes away. If it doesn't, THEN rotate the driveshaft. Make sure you mark it in relation to the pinion yolk before you do the u-joints so that you will put it back the same way. This way you will both solve your u-joint problem, and know for sure if they were the cause of the vibe.

Take care,
~Chris

rear u-joint solved it! thanx.

i guess i should of replaced it without doubts, but oh well, i guess they dont always last long used in racing.