So it starts around 40-45 mph, and then smoothes out, then comes back. It's starting to become more frequent and more violent, but never consistent. The tires are about 2 years old, everything else is real old. Any opinions appreciated.

 

in the front??if its in the front it might be the ball joints

 

Try this too, have the tires checked & make sure they are balanced.

 

check your u-joints also i had that problem with my 83

 

So what did you find?

 

tires balanced?

 

on U-Joint (rear)