Ok So I swapped a 1979 280zx 5 spd in the 71 240z. How do I get the speedometer to be accurate since the gear ratios are different now?

Change out the rear end to the same gears as the 280ZX?? I really don't know, but its a guess.

Check out this website and scroll down to where it says How to keep the speedometer correct and talks about the various speedo cogs.

http://datsunzgarage.com/engine/

Take it to a shop and let them calibrate it.

The speedo gear is matched to the rear-end gearing. So just use the speedo gear out of your stock 4spd. You may have to swap the speedo gear carrier... using the gear itself from your original 4spd., but put in the ZX speedo gear carrier. As I recall there is a "pin" that holds the speedo gear in the speedo gear carrier. (the carrier bolts into the transmission - and speedo gear is inside the carrier).

If you have changed the rear gear ratio - then you need a speedo gear to match it.

FWIW,

Carl B.

Sounds good thanks Carl!