Speedometer gear after gear change

[EVOrider]

I recently swapped 4.10 rear end in my 1983 Ranger. It originally had 3.45 gearing. Of course, now the speedometer is way off. I've read and tried to figure out which speedometer gear I need....but cannot figure it out.

2wd, TK5 transmission, 14 inch wheels, and 4.10 gears

Which speedometer gear is needed?

-Thanks

 

[kimcrwbr1]

You can possibly get a complete set of gears and do a trial error approach. Have you considered 15 inch wheels? Now would be the time and then use a gps to clock your speedometer if it is faster than your actual speed you need less teeth or if your speedo is reading slower than your actual speed you need more teeth. What engine do you have?

 

[bigmark303]

Have you changed tire size at all from stock? Otherwise with stock tire size and only a gear change its simple math.

New Teeth = Old Speedometer Gear Teeth x (New Axle Gear Ratio / Old Axle gear Ratio)

Pull your current speedometer gear and fill in the equation. If you have changed tire size you need to first find the gear ratio that would have corrected the tire size change and then calculate using that ratio as your stock ratio instead of the 3.45.

 

[kimcrwbr1]

http://www.ebay.com/itm/5-FORD-SPEE...Parts_Accessories&hash=item565d779bc0&vxp=mtr

 

[EVOrider]

I removed the old gear out and it is yellow which is 18 tooth count. I did the math formula....and it came to like 21.39. I figured the 21 gear is close enough....