Pipsqueak

I have an 80 N/A analog cluster.

When the speedo says I知 doing 55, my gps based speedo app on my phone says I知 doing 75.
The speed is off from the very start, and gets worst the faster the car goes.
I have replaced the log speedo cable from the piston to the pigtail (it got snagged on something in the road and got dragged to pieces), but have not replaced the one from pigtail to the back of the speedo.

I assume the issue is with the speedo piston. What I have now is a "white " 19 tooth piston
IF this is not the correct piston, how do I know what I need?
If you don稚 think the piston is the issues, what else do I need to be looking at?


Thanks

NismoPick

I think you mean "speedo COG" not piston.

You match the speedo cog gear to the differential ratio (non-stock tire size will also affect speedo). What is your diff ratio?

I have a picture of all the Datsun speedo cogs somewhere on ZDriver (it's from my Photobucket account, which I can't access at work).

Pipsqueak

I have no idea about the differential. how do i find that info? (yes im a Noob at this)
Tires are on the orginal rims and the correct size.

NismoPick

The FSM / Haynes states which differential for each model / transmission.

Try this too: Transmission Calculator - Z Design Studio

Before the speedo cable was ripped up, did it read accurately?

Pipsqueak

No. it never has ready correctly.

Zdon

o. it never has ready correctly.[ 1980ZX car has a 3:90 ratio rear diff which has a basic plastic colored spedo/cog. If you have any other issues it's in the gear behind the spedo/meter behind the dash.

Pipsqueak

Based on the FSM MT manual transmission page 15, I should have a 3.545, which on the website you posted says I should have a r180 differential. It reads like the 2 seat GL and the 2+2 (mine is a base coupe) have the 3.9
Which when I found this site Technical Information Page ..... Transmission points me to needing a 17 tooth cog.