The Stovebolt Site Forums The Shop Area Driveline Best way to increast gear ratio on low geared 1 ton

I have a 4.10 rear and run 235/85R16 tires; 70MPH for me is 3,100RPM. The 4.10 gears for the Eaton seem to be real easy to find, and they are very easily changed out since they are a third-member type axle.

Your transmission should be the SM420; they are still 1:1 in fourth gear, they just have a very deep first gear (therefor the name).

I'd personally just put a 4.10 third member in it and go. Changing rear ends, one piece driveshaft, trans swap, etc, is just making things hard on yourself IMO. (Unless you are planning to drive 70MPH all the way to work every day or something) You don't even (theoretically speaking) need to jack the truck up to swap third members.