Speedo issue-1966 Canadian Valiant [U.S. Dart 270]
 

Hi everyone-hope the summer was good cruising weather for everyone. I recently had an issue with my speedo on my '66 Valiant. While driving, I heard a slight noise [ could have been something on the road, not sure.] and thought nothing of it, until I looked at my speedo- I was most likely doing about 50 MPH, but the speedo only showed between 15-20 MPH. I disconnected the cable at the trans, it looks good, reconnected it, then disconnected it at the speedo under the dash. I went for a spin down the road, reached under the dash,and grabbed onto the inner cable. it is turning while driving. Any ideas? Could the speedo head or gear at the transmission have jumped or stripped a gear, resulting in an inaccurate reading? Anybody come across this before?