I'm having new 4.10 ring & pinion gears installed. Old ones are 3.55. Anyone know what I need to do to get the speedometer to read correct? Trans is an e4od and doesn't use a speedo cable. Guess it uses a magnetic pickup in the rearend. Does this need to be changed?

 

Read the tech article on this site:
https://www.ford-trucks.com/articles...peedorecal.php

 

Good article but it relates to different tire sizes instead of different gear ratios. I bet there's a similar article for gear changes, I just haven't found it yet.

 

Some day i'll learn to read posts more carefully. Gear ratio has no affect on your speedo reading. The reading is taken off the carrier which is downstream of the R&P. Only tire size affects the reading

 

So after thinking about this for the last hour (and just before I read your reply) I've come to the conclusion that I don't have to mess with the speedo after the gear change.
Thanks for the reply.