I just put 4.10's in maybe 300 miles ago and i went to remove trans today and took speedo gear out and its half way worn down already. Any ideas?

 

you put in the white 23 tooth gear, didnt you

 

ya....why

 

its not a ford part, and it isnt correctly calibrating your speedometer. If your car is a manual, you need to remove the tailshaft housing and replace the drive gear thats on the output shaft.

If you have an automatic... your **** out of luck