i have a 1991 300zx NA that i just bought a few weeks ago, the speedometer does not work and has not worked since i got it, when i say it doesnt work i mean it does not read the right speed at all, for example when im driving below 45 mph the speedometer will read zero about, but when i hit 50 mpg it will spike up and read about 40-50 mph, and when im going 70mph the speedo will read 100 mph, it seems to be very consistent with these readings, but i would like to get it working properly. the cruise control works, the tac works, and the odometer works. ive taken the speed ometer out and cleaned it with electrical cleaner. it didnt change any thing at all. from what ive read on other forums you need to just buy a new speedometer all together, but if any one has any ideas on how to fix this problem or has had this problem, it would be very helpfull to share what you know.

 

My speedometer is off as well. But doesn't do exactly what yours does. It reads about 10mph off the exact speed I'm going. The reason I know this is I got a ticket for going 71 in a 55 when clearly my speedometer said 60. I've been told its because my tires are too big. But I'm not exactly sure. I called a Nissan dealer and they said that's because of the tires and can't help. So I just keep in mind the my speedometer is 10mph over.

 

That seems insane to be because of your tire size. Does your speedometer read 10mph if you're going 20? If that's the case, your tires can't be to blame.

 

no, its all accurate up until about 45 mph. Which is really weird. But that is what everyone is telling, beacuse of my tires. So i dont know what else to do.