Speedometer Malfunction Question...

Hey everyone, its a cold ass day here in So.Cal, took my 72 Corona out for a spin and I hear grinding and bouncing of my Speedo. WTF! My speedo had been making funny noises recently but this was nasty. It bounces and goes all the way to the max starting from about 10mph or so. As I drove it, it got better, it didnt start grinding until about 40mph or so. I think as it warms up, it would get better but just reaching out to you all, do I need a new Speedo cable? Never replaced one, do I need to take the dash off or can I get to it under the dash? Anyone had this happen to them? Here is a video of my poor 'Rona...Thanks ahead of time.

just a follow-up. Later in the day I drove the car around again, it didnt do the jumping and grinding thing. Could it be that the grease within the speedo cable hardens up with the cold weather causing, somehow, this issue? (im just speculating and not basing this one any knowledge whatsoever,ha) Anyways, there is some cheap ones on the bay but just wanted to see if any of you that live in the cold weather has had this happen to any of your cars. It has gotten down to the low to mid 30's at night here, pretty darn cold for So.Cal, so just wondering. Thanks

i havent had this happen to me but some grease on the cable and the speedo might help you keep us updated