Hey,

I am experiencing a hard pulsing vibration when I am racing and reach about 70 mph and on. The tach is about 3,500 rpms when it starts. It continues when I stay on the gas and when the engines winds down once I let off the gas pedal. It doesnt happen in any other gear or speed. Just when pushing past 70 at 3,500 rpms or so.

I have a 350 tpi with 120,000 miles on it. I just had 3.73's installed a couple months ago. I only experienced it after this swap, but it may not be related because its just that I have been racing faster, and at higher rpms now to realize such a vibration.

I did a search already and was wondering if anyone could rule anything out right away, or have any probable idea on what this gemlin is.

Thanks

 

In case it helps anyone. The problem was my tires. I must have shifted the belts in them. Once I changed and put on my MT's, no more vibrations.

 

I've had a solid trans mount cause a similar problem. Switching to poly solved it.

 

Just about every vibration problem I had was solved by the following:

1.Wheels: Take your car to the tire shop have them make sure your rims are not bent and true, and balance them.
2.Trans mount: common failure point causing odd drive line angles.
3.Drive shaft: If you're running the stock steel shaft, remove it and have a trans shop or drive line shop balance it, BUT... Buying a fourth gen aluminum one from a ls1 or lt1 car is a direct fit and is much lighter, and might cost the same as the balance of the steel one. (I did this swap and was very pleased) no vibration at all.
4. Worn front suspension components (jack up the front and move the wheels front to back side to side make sure theres no slop, if there is ball joints may be cause) also pull on the centerlink and tie rods, should be no slop, if there is replace.

Run through these things and you should be smooth sailing. (BTW: my main issue was my drive shaft) May not be yours, just saying...