1990 lesabre speedometer problems

speedometer works only when it wants to. sometimes you can hit bump and it will start working. i have replaced speed sensor with no luck. i have even put car on jack stands started car put in gear and tugged on wires and tapped on instrument cluster trying to duplicate bump in road with no luck help!

Same here, exactly! Hit a bump and it may work 10 minutes. I am unable to simulate by bumping either.
Did you find out the root cause?
Thanks,