Speedometer Gone Wild

[Marco7]

1991 TLC 3FE

Last night while on the freeway going about 60 mph(48 degrees F outside temp), I heard a noise that sounded like the tazmanian devil was directly behind my speedo.
A quick check of all systems showed good, except for the speedo itself...pegged at 120mph while going about 60.
I immediately exited the frwy, and turn right into a parking lot. As my speed decreased so did the racket but what's odd is that it went completely silent/normal as soon as I turned my steering wheel to the right for my turn.

Made a u-turn to the left and got back on the feeder road and continued to drive it but didn't exceed 50mph...still silent/normal and the speedo operating normally now.
Today, all was normal, but I never did get up to the speeds that caused the chaos.

It sounded like the cable became disconnected directly behind the speedo, but how could it be intermittent if this were the case?
I was afraid the friction from the loose cable whippin' around back there might cause other problems, if this is indeed what's occurring.

Anyone else encounter this problem?

 

[Koffer]

sounds like the grease in the speedo is getting stiff or the nylon bushings are crapping out and they are letting the needle cup rub against the speedo cable shaft end .

 

[Marco7]

sounds like the grease in the speedo is getting stiff or the nylon bushings are crapping out and they are letting the needle cup rub against the speedo cable shaft end .

Thanks Koffer, sounds like I'll be pulling the dash panel to see which it is. While I have it out, guess I can replace most of the bulbs that seem to be burned out.

 

[grizzlygibbs]

I would check under the rig before I ripped apart the dash?

 

[AZ91FJ80]

I'm encountering this same issue now, and any helpful suggestions, pics or links are welcome, please?

**UPDATE**

Nevermind; I found this thread: HELP - spinning/grinding/buzzing noise???