ratedZ

Hey guys, I got a ticket for speeding the other day...if I remember correctly, my speedo showed around 95-100mph before I got pulled over. The officer told me that he got me at 80+. As you can see it’s off by a lot. Here’s some history of things I’ve done to the car that has affected the speedo. Swapped out the electronic speedo to the 79 280zx 130mph speedo. I originally used the speedo cable from the 79 280zx but I had to replace it with one I had laying around from the original set up because the speedo would jump up and down at speed. So now I’m using the cable that came with the electronic. It seems to work but it’s still off...I don’t think that using the speedo cable from the electronic set up is the problem as I’m having the same exact problem even with the 79 speed cable. Other than this mod, everything including the tires are the same 225/60ZR15 on 15x7’s...didn’t touch anything else. I’ve been to the Datsun Garage and read about the different cogs....I don’t think replacing the cog will help my speedo read accurately as I never touched the differential. Sooo, I need some help. Should I go out and grab another speedo cable for the 79 cluster? or do you think the speedo gauge it self could be faulty (it came from the junk yard). I don’t need it to be dead on accurate but I would like to have an idea of how fast I’m going...can’t afford another ticket Thanks all!!!