I now have a Ford Expedition 4x4 with 3.55 differential, the ring gear is 9.5 inches and 31 axel spline and I would like to change to 4.10 ratio. The problem is that, if I'm not mistaking is that Ford doesn't make higher ration than 3.73 with this set up. Do you know if there is a reliable company that makes a 4.10.
Thank you for your help

The 9.5 is made in a lot of different ratio's. Check with your local speed shop.

Wannabe

2WD or 4WD? if the latter, you have to change both ends.

Check 4wdparts.com

Thank you for your help.
I have found what I was looking for

Make sure you do differential clutches in there if it is limited slip, they have had lots of problems on the EX with the clutches warping and chattering on turns. Since it is apart it is only like 90 bucks in parts to repl the clutch pack.