1996 Nissan Maxima sometimes the spedometer will drop to zero while driving?

while driving my 1996 Nissan Maxima sometimes the spedometer will drop to zero, recently i press the odometer reset and it came back on. sometimes if it dropped again, i can hold in the odometer rest and it will come back on. can anyone tell me what is causing the spedometer to drop?|||Your speedometer head is finished. You can buy a used one on ebay. Or in a junkyard. I've done that for a 97. The entire cluster, all the instruments , should cost less that $100. If you search on youTube, there's instructions on how to change it. Don't go near a dealer.