I own a 97 f-150 4X4. im planning to swap the 3.55 gears for 4.10's. im going to keep the same tires i have which are around 32 inches tall. I need some help finding out which speedometer gear i need , im thinking a 21 tooth but not sure, anyone have any info?

 

TN,
You can check here for a calculater that may help
http://www.finer.com/internet/pages/speedo.htm
Our transmission uses the 8 tooth orriginal (trans side) gear. I think the 21 tooth gear will probably work. I am using the 23 tooth gear with my 430 rear and I orriginally had 355's. My speedo is reading a little fast with the tires I now have.

 

just so you know FORD most likely wont have the gear for 4:10's...because 4:10's arn't stock on any ford...i had to go to a speed shop for mine..

 

The 21 tooth is available at Ford, the 23 tooth is not.