I had the same problem on my '62 Suburban. I happen to have a friend who runs a company called AutoInstruments, and they restore old gauges. I called him up, and he said to immediately pull the truck over and disconnect the speedo cable. The squeeling and irratic needle are in the head, not the cable.
He told me that if I didn't disconnect the cable right away, the head would blow up, and then it's unfixable.
Naturally, I didn't listen to him and drove for two more days.
Naturally, the head blew up. Fortunately, I found another nice one in a junk yard and am using it.
He was a friend, not some guy trying to make a sale. And he was dead-nuts right when he described what would happen.
Brad
