Well i was getting a vibration starting around 50mph and at about 95-100 it was pretty bad. So today i decided to change the U joints, now the vibration starts around 45-50 mph and by 80 its so bad u don't want to go any faster. U joints where installed right so i have no idea why. Going to take the driveshaft back out in the morning and see if everything looks okay. Im starting to think a trip to the junk yard and a 4th Gen driveshaft can come home with me for $15

Edit: My car has a factory aluminum driveshaft

 

sounds like the DShaft is out of balance

 

Check near the ends of the shaft. If you're missing a balance weight, you should be able to see where it once was.

JamesC

 

It has all of the weights on, i just double checked.

I'm thinking about just going to pullapart and getting another shaft, they have a few 4th gen, i could get one for less than $15. Who knows, i might get lucky and find a 6 spd transmission to lol

 

Have you considered tires and/or wheels? How about alignment?

JamesC

 

My first car was a 89 RS had a set of cragers on it and it did the same thing, But didnt know what it was till i changed the rims the cragers were bent or had oblong lug holes, it was bad to dash would shake "or more like jump" after i changed the rims the car was smooth. If you can just to check try and swop your rims for a friends for a test drive

 

I don't think it needs an alignment because the steering is smooth, last car needed a alignment and at 60 the steering wheel was vibrating. I could try a different set of wheels though, the back could be either bent or out of balance

 

I had the same problem. I had my driveshaft balanced and installed new u-joints and still had a vibration problem. I took it to (2) driveshaft shops they both said the driveshaft had a slight wobble meaning it was not completely straight so I changed the driveshaft and the the problem went away. More than likely your driveshaft is slightly bent. For $15 buy the junkyard shaft and try it. Worse case scenario you'll have to go back and buy another if the first one doesn't work. Just make sure to check the u-joints to make sure they are in good shape.

 

Well i put new joints in mine and it still sucks, I will find me another aluminum one at the junk yard and try it out, It would be nice if $15 bucks fixed it

 

Have you had the wheels balanced lately...?

 

Double check your pinion angle.