Technical ? Ford AOD Speedpmeter gear

I have a stock early 302 and Ford AOD tranny in a modified lakester. Using electronic speedometer. Winters rear with 3:78 gear and 750 16 Coker rear tire (31” tall). ? Which speedometer gear to use?

 

My AOD has a mechanical speed sensor. You will probably need a GPS based sending unit

 

Will it matter? If you have a 'learning' speedometer, simply setting it up will do the trick, what gear you have won't matter. If you bought a speed sensor specifically for the speedo, you need to know the pulse rate per mile. You also need to know if the drive gear in the trans is a 6, 7, or 8 tooth gear.

'Standard' Ford pulse rates are 8000 pulses per mile. Here's a calculator to determine which driven gear you need...
http://www.classictiger.com/mustang/VSSCalc/FordVSSCalculator.htm
Your 31" tall tire turns 672 revolutions per mile, plug that in along with gear ratio, etc, and it'll tell you which gear you need.

 

I'd have to ask what speedometer and what sensor you have for it.
If it is working and off and there is no adjustment, use the page Steve gave along with a GPS that will tell your exact speed as compared to the speedometer's reading to figure the percentage difference and figure out what change of gears you need.
You can download some pretty good gps speedometer apps on your phone if you don't have access to a handheld gps. Sure beats the hell out of running down the road beside your buddy at 60 waiting for him to give you the "got it right on 60" sign. to tell how far it is off.

 

Do it old school. Order the 5 or 6 different tooth counts Ford made, and try one after the other until you get it right. They aren't that expensive, and that way you will have options if you change rear end ratios or tires at a later date.

 

"Sure beats the hell out of running down the road beside your buddy at 60 waiting for him to give you the "got it right on 60" sign. to tell how far it is off."

That actually sounds kind of fun. And nostalgic.

 

Check the car on a measured mile, say you come up 9/10's in a mile your running 10% slow. Ford driven gears are 5% per tooth 2 teeth less will speed it up 10%.,
No guesswork involved.