Speedometer problems

I just installed a new speedometer cable from the transmission to the speedometer hookup (push on - clip type) on the back of the dash bezel in a 1969 Valiant. While driving, the speedometer needle goes crazy! It wildly bounces back and forth and is registering 80 to 110 mph when I know I'm going 30 mph. There are no kinks or sharp bends in the cable at all. Anyone ever have this problem?