Speedometer Trouble

Well, I got sick of the wife complaining about the speedometer not working in our 67 Cuda convertible so I went out and bought a new cable and installed it. Now, heres the problem. The car doesn't move 2 feet and the speedo jumps to 20-30mph. I disconnected the cable from the speedo and brought the end out under the dash to watch it spin and it looks to be spinning correctly. What gives??? The speedo is a 150mph that I removed from another cluster and installed in my car, so it's origin is unknown, but I have not had this problem before. Any suggestions? Thanks, Geof
Author: admin