I had a shop install 3.73's for me (a reputable race shop that my instructor recommended), and since, there has been a vibration once you go about 80. Not a car shaking, rear view mirror bouncing vibration, but more like a loud noise that you can tell is a small vibration. What could this be? Could they have installed the driveshaft out of phase? (whatever that means). It's kinda hard to get on the highway after the hurricane that just came through, so I thought I'd ask rather than try 10,000 different thigs by myself.

 

The drivshaft could be out of phase. That just means its not installed the way it was supposed to be so it is slightly out of balance. It could also be that the new gearset is just noisier than the old one. Since it happened after they did the work i would take it back there and have them fix it.

 

definatly take it back to whoever installed it ...that way they cant say you messed with anything

 

keep in mind if your drive shaft now has to turn alot quicker and more often to do 80 mph (any inballance is now magnified) not really there fault.

 

The thing is I just bought a LS1 shaft, used. Could it be so out of balance that it vibrates at 80?

 

If you went from a typical TBI type of gear like 2.73 or 3.08 to those 3.73s, your drive shaft is now turning the RPMs at 80, that it used to would have been turning at about 110 or 120. Some amount of increased noise is normal. This happens all the time; it's not the gear installer's "fault", except to the extent that it resulted from the fact that they did the installation.

You can take the shaft to a balance shop and make sure it's not out; look at the U-joint caps where they go in the rear end yoke, and make sure they're all the way down in the saddles like they belong (clips not sitting up on the saddles). Put the car up on jack stands under the axle tubes, have somebody sit in it and run it at whatever speed it starts to vibe, look at it and see if you can tell which end it is; try balancing it yourself (crudely) with a hose clamp, and see if you can make a difference.

 

Well, I took the driveshaft in and had it balanced, and it fixed the vibration a little bit, but at like 90+ the car vibrates very fast a little bit, like if you felt an electric motor spining fast. Is this just normal with aluminum driveshafts?

 

No; but it's normal with higher-number gear sets. Remember, at 90, it's now spinning as fast as it used to be spinning when the car was doing 120 or 130.

 

just curious as to which aluminum driveshaft you have? I think the LS1 driveshafts are rated at a much higher top speed than the 1LE. Like RB said you never felt the vibe at 80-90 before, but that's because it was probably at 120-130 before.

 

It's a LS1 driveshaft.

So is there nothing that can be done to fix this? What about buying a new aluminum DS? I don't really want to fork over $800 for a carbon fiber one, but if I have too...

 

It's normal. Why would you "have to"?

 

I had the same problem with mine-sent the dshaft off to get balanced. They said it was bent and they could not straighten the alum-they only work with steel. So they shipped it back to me and I spun it in a lathe with a dial indicator on it-it was .070" off center at the u joint-not bent. I pushed the ujoint .035" (or so) with a press until I had it to less than .010" of "wobble" and now it is perfect-no shake anywhere. I had to push the ujoint against the spring clips that hold it together to the point of putting pressure against the side where it was tight-but it cured the problem.

 

I really don't like this high speed rattle, it just doesn't feel right. Oh, and the guy said the "wobble" of the DS was between .010 and .015.

 

I'm thinking of buying the Lingenfelter 3.5" aluminum driveshaft for $300. Critical speed of 11,000 RPM (that would be 190 MPH in my car, like it could ever go that fast ). Anyone have experience with it, and more importantly will it stop the vibes?

 

does the LS1 type have a balancer on it - around the tranny yoke ? i had the same problem with my stock steel shaft and 3.73's.

 

it sure does, but I think that's more for harmonic vibrations, not ones that are caused by balance

 

hmmm . . . in that case you may want to double check your geometry. I had the exact problem with my stock steel driveshaft and the problem abated completely when I switched over to the LS1 driveshaft, and a spohn torque arm which changed the pinion angle slightly.

 

Could the tranny be vibrating? Is it possible to run the car without the driveshaft in to see if it is the tranny vibrating, or will bad stuff happen?

 

ttt