Just installed a 3.636 diff with 6 speed gearbox. Runs great. only speedo is off. (not only found in australia, europe has them too)
60 km/h on the speedo = 70km/h on GPS
I also looked at the speedo options and found a suitable match. BUT: it was calculated from 92+ miata's using 22teeth speedo gears.
Mine is a 91 model with 20 tooth...
Is there also a difference in the meter itself??

What is my best option for a fairly accurat speedo??
From my calculations:
91 model has 4.3 diff with 20 teeth sensor.
New diff has 3.636
3.636/4.3x20= 17 teeth...
Is that correct???
Can i use a 84-85 speedo from an RX7?? (pnp on miata speedo cable??)

 

I was running the same setup. You can choose an M502-17-441 (19 tooth) gear or an M503- (20 tooth) gear, it depends on what wheel/tire combo you are using. With my 205/50R15 my speedometer was barely off compared to the GPS.

This is what I used to build the gear setup (all parts can be ordered from Mazda):

1011-17-442A - This is the sleeve/housing that will position the gear in the proper location to engage the gear within the transmission. If the sleeve that comes in a 5-speed transmission is used, the smaller 6-speed gear will be free-floating and will not engage. Thus, no readings.
M502-17-441 - This is the actual gear.
9922-20-214 - Spring Pin for holding the gear in the sleeve.
9958-60-8166 - Oil Seal for inside the sleeve.
1011-17-443 - O-Ring for the outside of the sleeve.

 

Thanks for the info.

 

Why don't you ask for 2 of each and I'll pay you the other one?

You know I can't get it myself.

Let me know.

 

Thanks for the info, but it does not answer any question...
I have a 91 miata, that already has a 20 tooth gear...

 

I wouldn't have posted the information if it didn't answer your question, but because I didn't clarify in my previous post, the 20 tooth gear you have is the wrong diameter and will not work.

I posted this same info when you were having issues with the gears. https://www.miataturbo.net/forum/t41362/

 

sorry to thread jack, but which one am i suppose to run with a 6 speed /w 3.9 final drive?