I do not think you can use a 3 series gear with a 4 carrier. I was looking for a posi trac unit and have 3:73 gears, they had to go to the 4 series carrier for this ratio. Do not know about the Richmond gears. Call here 918-425-7725 Axle transmission and transfers ask for Richard, he can give you the low down. Kieth
That's the advantage of going aftermarket. Richmond makes higher numerical ratio gears that fit into the 3 series carrier. You can go all the way up to a 4.56 gear in a 3 series carrier. Notice on this link how they have the steeper gears for a 3 series carrier:
http://www.richmondgear.com/07Apdfs/page27.pdf
