Technical Ford Speedometer Drive Question

Hi Gang,

I want to run a closed drive line banjo on an AV8 with a Ford speedo.
how do i know which speedo drive to choose?
There are 18, 19 and 21 teeth as far as i have seen.
i guess it depends on the differential ratio and tire size?!
Which combinations needs which turtle?

thanks guys´n gals

 

They aren't expensive, so grab one and give it a try. Then you will know which way you need to adjust, if possible. You might find that none are gonna get it perfect (I did). You might need an inline ratio change box. A good speedo shop can make a box that will give you a perfect reading speedo.

The gear on the driveshaft is the same for all the turtles.

 

ok will do
thanks alchemy

 

The Green Bible has a table showing which one you need for stock ratios and tires. If you post your rear end ratio and tire size maybe someone could help. The turtle should match the teeth on the gear.

Charlie Stephens

 

I have a turtle assembly, and the worm gear if you still need one. I'll have to double check the number stamped on it.

 

Yes, you don't pull the gear out of the turtle. You just switch out the whole turtle. Each turtle housing has a gear centerline a bit different from the other to make the driven gear spaced properly from the driveshaft.

 

@Charlie Stephens: i found the speedometer cable table but not the one for turtles. i can see it referenced as " speedometer gear chart" but where is it hidden?
thanks

 

Look on page 632 of the Green Bible.

Charlie Stephens

 

thanks charlie i have an old original Ford chassis catalogue. it doesn´t have that page..

 

I'm at work with no catalog...but try the 17,000 general part number section, where speedometers live along with other small systems. Unless using actual original sizes, try to match your tire diameter to an original size in the diameter and ratio chart.

 

Most speedometers are 1000 rpm = 60 mph. If you know your tire revs per mile (some manufacturers have that info on their website) and axle gear ratio, you can figure out the speedo gears necessary.

 

thanks for the hints guys

 

If you are using tires that are not on the Ford chart, you will need to find out diameters of the tires shown and match up your tires. This is an inexact science since tires are not all that uniform, especially over several decades, but you should be able to come close by just asking Hambers about sizes of particular tires.