Have a late 99, dually, 4x (60 front 80 rear) wanting to swap to 3.54, found in dodge's. wondering, if dodge d80 rear shafts are the same length and bolt pattern as the ford 80 rears? I believe the ford was 37 spline, where the dodge was 35, hence the desire to swap shafts as well. I have a 4.10 now, otherwise I could just swap gears. Had I ended up with a 373 truck, the 354 gears would go right on that carrier, and no worry about the shafts.

Hopefully someone knows!

 

Why not just get the 3.73 carrier from a ford d80 and be done. Your already ahead with that. I imagine you think your going to get better fuel mileage moving to the 3.54 ratio, I think otherwise, my belief is that your going to see same if not worse fuel mileage and its going to strain your tranny, but whatever.

 

you might see a little better mileage but you will never recoup the cost of the gears.

 

I like the notion of changing for the mileage its gunna be an in town pooch with those but moving on. I think dodge runs a narrower housing than ford at least they always used to back in the 80's and 90's