I've read a number of threads involving speedometer issues, but, nobody has ever really answered the question I'm about to ask. I know it's electrically operated, and can have issues in either the gauge circuit board or the differential.

What causes the speedometer to occasionally stop working? I don't think my problem is in the differential because on the occasions when it doesn't work, it will start working again if I slap the dashboard, and works fine until the next time it acts up.

Seems to me it has to be in the cluster somewhere. All the other gauges work fine, just the speedometer acts up.