Serious steering wheel wobble

[cfauvel]

my 69 Mach1, has a seriously violent steering wobble at about 70mph up to 80 mph, then quiets down from there on.

I run stock wheels with BFgoodrich 215/60-14 all the way around.

Does anybody have an idea of the cause?

Tire balance? I've had all 4 tires re-balanced
Wheel out of round? (no clue where/how to test this.)

Drive Shaft out of Balance?

Bad ball joints? ( wheels wear perfectly even, and the car runs straight with no pulling, but I believe the joints are original)


The wobble is best described as the whole steering column girating up and down rather than just the steering wheel having the shakes.

Thanks

Chris

 

[MrBobMarley]

I had a similar problem, but mine was only the wheel wobbling. I put new universal joints in the driveshaft and it went away. My column is and was solid as a rock. Is your column strap(if there is one) tightened down?

 

[cfauvel]

The column is secure in it place...the u-joints are relatively new ( < 500miles).

I'm going to try to get the drive shaft balanced, but I seem to remember out -of-balance drive shafts were felt through the entire car in a harmonic (sine wave...at a certain speed the car would vibrate then stop then vibrate several times per minute in a pattern) way.

any other clues?