Sudden violent vibration …

[draggin49]

I recently purchased a 36 ford roadster , original drivetrain . It had driven pretty smooth up to this point . I was on a drive last night and suddenly the car began to shake violently, I was having to really hold onto the steering wheel it was so bad . I limped the car over and called AAA and had it towed to my house . Any ideas on what might be the culprit or how I might better figure out ? Should I try and pinpoint when the vibration starts ? Or if it still vibrates if I put clutch in ?
Any tips or insight is appreciated