Colin Double, Stillwater, OK, 1971 Dodge Challenger 383

I have a question about my speedometer. I have a 1971 Challenger 383 w/ a 727 tranny. Last winter when it was slick I accidentally spun my tires and my speedo just went dead. When I took a closer look my cable broke. I bought a replacement and installed it. When I drove it for the first time my speedo was making a clicking noise but worked fine for the time being. I then drove back home (about 80 miles) and when I got home my speedo needle did not go below 20 mph. When I left home my speedo worked fine except that it read 20 mph fast. When I arrived at my destination the needle did not drop past 40 mph. I unhooked my cable not wanting to do any more damage to my speedo. My question is do you know what happened to my speedo and if you do what can I do to fix it if I can fix it.