Drive train viberation

I just got this 81 last sat. Having run it for a few days I see that I have a viberation. Around 35,3700 RPM it starts. It's a drone that comes and goes every 1/4 sec so it's pretty constent. The info I have on the car is that it's got a 350 HO GM crate engine turbo 400 with a "mean shift kit. Trans has been rebuilt. A 1,200 stall. The driveshaft has been "rebuilt"?? along with the rear shafts. If I go to 4,000 RPM it goes away. The only experience I've had in the past with this type of problem was a 70 Z/28 that I bent the driveshaft in. Other than that the car is real strong. The PO who I know has put $16,000 into it over the time hes owned it. Any idea of where to start to track this down?? Thanks

If it is RPM dependent, it will be engine/flywheel related.
If it is speed(mph) dependent, it will be driveshaft/halfshaft/tire related.

Usually, engine or flywheel vibrations are constant, meaning it's always there, just worse at certain rpms. You can also get the vibration without the car moving, if you raise the rpms.

Driveshaft/tire, or "speed" dependent vibrations can come and go at different speeds, and may get worse, or better at times. This type of vibration will only happen while the car is moving.

You say it "comes and goes every 1/4 second"...1/4 second??? You've got a good sense of timing if you can count that fast!

From your description, I'd say start looking at the driveline first.

I agree with Adam, years back I had a vibration issue in another car. After balancing the tires, then purchasing new tires, brakes and turning the drums, (it was a '64), at the end of all that I replaced the tube in the driveshaft and the vibration went away. ...so it probably is in the drivetrain

[QUOTE=Adams' Apple]If it is RPM dependent, it will be engine/flywheel related.
If it is speed(mph) dependent, it will be driveshaft/halfshaft/tire related.

Usually, engine or flywheel vibrations are constant, meaning it's always there, just worse at certain rpms. You can also get the vibration without the car moving, if you raise the rpms.

Driveshaft/tire, or "speed" dependent vibrations can come and go at different speeds, and may get worse, or better at times. This type of vibration will only happen while the car is moving.

You say it "comes and goes every 1/4 second"...1/4 second??? You've got a good sense of timing if you can count that fast!

From your description, I'd say start looking at the driveline first. [/QUOTE] Adam, I'm hurt!! You know I work in the Aerospace ind. I can count things in my head into the thousandth's and won't be off but a tick. LOL!!!!. Really, I can see in my reivew- mirror the comming and going of the vib. it gets clear and vib. back and forth in less then a second interival. I'll check without a load and see if it's still there.

Michael,

Do you work at Gulfstream?

Hey 'Gator,

[QUOTE=ranger3]Michael,

Do you work at Gulfstream?
[/QUOTE] Yes I do. 22 Yrs.

The problem is speed related. If there is no load theres no viberation. I guess I'll start with the east stuff, like checking to see if I lost a wheel weight. I remember taking a test drive in it before we made the deal and it a smooth at that time. That was last sat. I brought it home and didn't drive it until the next day and I don't remember it doing it then either. I'm not sure when it started. This morning I kept an eye in the tach. It starts around 2500 and goes away around 3200.