Hey guys. Well, ever since I got my car I have had a vibration at higher speeds (above 70 mph with 3.42 and 60 or so with 4.10s). Now, to make the long story short, car has different gears, diff, tires, wheels, shocks, coils, u-joints, etc, etc.

Today, I cranked it up high to almost 150 mph after I did some tuning and mods, and be damned, after 128 mph or so the vibration just dissapared. Smooth as silk. When I went to slow down, kept it in 6th, the moment it hit 128 mph again the vibration started.

I have a 1LE vibeshaft. Had it rebalanced, checked, new u-joints. They said it was ok, only had a little runout.

I think this driveshaft is bowing at those speeds, and then goes smooth at high speed when it works itself out of the frequency. Sounds reasonable? What do you guys think? What else could 'cause this type of vibration that acts like that.

And lastly, do you think a custom aluminum shaft would solve this problem. Not cheap, but cheaper then retail LS1 shaft here in Calgary, plus I would like a nice, custom built unit. Thanks guys.

 

The 1LE isn't known as the " Vibeshaft " thats the factory steel unit.

 

I know, but I was just trying to show my frusturation. So, does it sound like this could be it. I can't see it be anything else that would go away at high speed.

 

This would tell me that it's not your driveshaft.
The shaft is spinning at the same rpm it always has - regardless of gear change. It's the rear end gears that make the wheels spin faster, not the driveshaft.
There's nothing much you can do to change the rpm of the driveshaft at any given speed - except get the tranny gears changed.
Futhermore, you've been told that your DS is balanced.......I would look elsewhere for the problem rather than throwing in a very expensive custom DS.
Good Luck!

 

Well, I have not had the speedo recalibrated, so I am guessing the speed it comes in as. What else could it be thought, that I have not changed yet? I changed the diff, then the gears, then most of the suspention, etc, etc. I do have urithane tranny mount, yes its worse with it, but its still there with a rubber one. I just don't see it be anything else that would work itself out and back in like that.

I was thinking of putting the car on a hoist with the suspention compressed to simulate driving, then running the car and watching what it does from underneith. How safe is this? Thanks guys.

 

These 4th gen cars are very touchy with respect to drivetrain noise and vibration. I chased severe vubration problems with my M6 car for over a year. Here are some major contributors that I found.

1) The bushing in the tailhousing is very short and can wear. This allows transmission yoke wobble and will set up some crazy dynamics. My output bushing was actually "out of round". I believe that most of this happend when i broke an aluminum shaft about 1 foot back from the trans and the piece slung around for a while punishing the bushing. This bushing problem can be made worse if you get a trans yoke that has ID splines that are broached on the high side of the tolerance. The last time I redid my trans I installed a Viper main shaft. The viper rear bushing is larger diameter and much longer. This provides way better support for the trans yoke and tightens things up nicely. This solved about 10% of my problems.

2) When I redid my 12 bolt, I used a Ratech solid sleeve on the pinion. Sound's great but, The Ratech's are a POS IMO. The faces of the sleeve were not machined parallel. When the pinion nut was cranked down the get bearing preload, the Ratech threw the yoke way off of center. I'm talking a lot! With the driveshaft installed I was reading .027" difference from one U joint cap to the other at 180 degrees. So I ditched the Ratech solid sleeve and went to a Strange machined solid. Reassembled every thing and Runout was .004" - Pretty respectable. This pinion yoke deal was probably 90% of my problem.

3) Make sure you have a good driveshaft. This is the obvious one! The LS1 aluminum shafts are pretty darned good from the factory and if your not launching hard on slicks it will hold up fine. I bought a Denny's steel Nitrous Ready shaft. Denny is a great guy and stands behind his work 100%. His shafts are balanced in a high speed balancer. This guy knows his stuff.


Hope my rambling helps,

Steve

 

It would have to be only at a certain RPM in order for it to be driveshaft related.

Edit: I'm confirming you're right, by-the-way....