Speedometer cable going bad?

[Ken O.]

So the speedometer on my 67 GMC started making some noise above about 35 mph a couple weeks ago. When it does this the needle starts wavering up & down, (usually up to about 50 or so) Well this morning on the way to work it really started getting loud and started flopping from 0-120 or so. I assume this is the speedometer cable going bad, correct? When it happened in other vehicles it just stopped working period. Never had one go nuts and start flopping around before. haha!