Looks like 2wd to me

 

According to the information that I have, the stock rear end for a 75 F250 is a Dana 60 M61-1. Unfortunately, exactly what this means as far as gear size vs mileage is a little bit beyond my current level of mechanical knowledge. I guess I could also use a bit of assistance in exploring the possibility of installing an upgraded rear end gear package too.If anyone out there has had any real success with increasing MPG via this method. I'm sure that everyone would like to hear all about whatever you may have done.

As for the suggestion of increasing the size of my tires. I'm already running on a new set of Michelin LTX A/S tires (LT265/75 R16) Although the upgrade in tire size from my old LT245's to the LT265's did provide about a 15% increase in my overall mileage. There also seems to be an almost exactly the same 15% difference in the ratio of real miles traveled to the miles actually being displayed on my odometer (1.0 to .85) Considering that this truck is now over 30 years old, I really don't know if it's even worth the effort to fix the odometer to track properly.

One final comment:

I'd like to express my sincere appreciation to everyone who has responded to this posting!

You guys are the best!

Larry Bailey a.k.a. "75 SuperCab"

 

Go to a big truck salvage yard they might have a 5831spicer 3speed I had one in my 75 supecab 4x2 they are 15 percent overdrive I bought mine for 350.oo$
Dale

 

Any idea on the axle ratio? Or do you know your highway rpm@speed?

I went from 4.10 to 3.21 on my Suburban. Highway went from 13mpg to 17mpg. I dropped a solid 500rpm at highway cruise speeds. City mpg stayed at 13 until I put in a manual trans, now its 17mpg no matter what I do. I run 33" tires also.

I know my 6.2L diesel is more rpm/mpg sensitive than a gasser, but on the other hand, a 460 has more torque so that should avoid some downshifting.

I believe 3.07, 3.31, and 3.54 are the more highway friendly ratios for the F250's Dana axle.