NP208 speedometer gear

[WP77]

I just installed a rebuilt NP208C in an 87V10. The rebuilt case did not have the driven speedometer gear, so I used the one from my old Tcase. It was a light green color. Before, my speedometer was accurate. I have factory 3.42 and 31x10.5 15 tires. Now the speedometer is about 12-13% slow. Can I fix this with a different driven gear, or do I need a different drive gear?

 

[Chevy 88]

I don't know much about them, but I think you need one of these. I think you can get them with different gear ratios to make the spedo accurate:

 

[Camar068]

try this:

https://www.tciauto.com/speedometer-gear-calculator?srsltid=AfmBOopuax86qM1iKbdvIHah52W_AhFoBYoEtsOqpaFsmEZMwU8eJaF8

https://www.73-87.com/7387garage/drivetrain/speedo.htm