My speedometer clicks and bounces, how do I fix it?

If this is a datsun and not a nissan name plate then you need to check and see if the speedometer cable is sticking or binding.if it is you can remove the inner speedometer cable from under the dash you have to remove the speedometer cable from the back of the speedometer head and move were you can work on it under the dash,turn the inner cable by hand to see if you can feel it bind or turn roughly before removing it,pull the inner cable out from the outer cable wipe it down and as you re-install it lube the cable with a light grease all the way to within the last 2-3" and re-install to the speedometer head and drive to see if it fixes the problem.usually this fixes the problem however if it doesn`t then the speedometer head is the problem