I have had my 80 rx7 for about a year now, with no troubles until a couple of days ago. Driving it, and all of a sudden the vibration started to shake pretty badly, i can feel it a lot more when i have my hand on the shifter.
It doesn't occur when I am not moving, the motor sounds fine still, but the transmission is a little rougher to shift now, and the clutch has been starting to slip. Also once i get into third gear around 30mph is when it gets the worst. It is there the whole time while driving but peaks around 30mph.
Any ideas?? Could it be the transmission?

 

Driveshaft

 

Or clutch . Easy fix there

 

Cool answers had the same problemo.