My '97 doesn't have the computer controlled speedometer, I guess. I used to have a Superchips programmer, and it didn't allow me to correct for tire size, so I'm guessing that means it's a mechanical speedo.

How do I change the speedo gear, and where is it located? I'm considering swapping to 4.10 gears for better towing, and need to know how to correct it.

 

Look on the tail shaft of the trans/trans case and there will be a small, round thing attached with a wire coming off of it. This is the VSS sensor. Clean up around the area and remove the single nut and remove. Be carefull, because there is an O ring seal and you don't want to mess it up.

On the end will be a small plastic gear. Count the number of teeth on it. With a 3.55 rear end and stock 16" tires, it should have 20 teeth. With the stock 17" tires, it should have 19 teeth.

Depending on what size tires you get/have, will also factor in to what new gear you will need when you go to the 4.10's.

In my case, I upped the tire size, but didn't change the gear ratio, so I had to drop a tooth size. If I had gotten the same size tires and changed my gear ratio to 3.73, then I would not have needed to change the VSS gear at all (the 20 tooth would still be correct). If I went to a 4.10 ratio with the same size tires I have now, I would probably need a 21 tooth gear.

Find the VSS sensor first, then you will just have to determine what new VSS gear you will need. They only cost around $10 at the Ford parts counter, so it's not a big deal if you don't get it right the first time!

Good luck!

Mitch

 

Thanks!

It's just like the Jeeps then. I haven't had ANY time to crawl around under it to figure this out, so that's why I asked the question here.

I've got 265/70-16, stock was 235/70-16. Any idea what tooth count I should be using?

Once I change from 3.55s to 4.10s?

Thanks,
Tommy

 

Your new tires are about 4% taller, which will make your speedo/odo indicate 4% low. Your new gears will be 15% lower which will make your speedo/odo indicate 15% too fast. With the combo your speedo should indicate around 11% too fast. To correct this, increase the tooth count on the plastic speedo gear 11%, or as close as you can get it (for example from 20 teeth to 22 teeth, if that is available.)

This assumes your speedo was accurate with the factory combo of gears and tires. An alternate method would be to get the gears installed, then take a ride and check the speedo/odo with a GPS to determine how much actual percentage correction you need.