I got a 1985 ford - f250 w/ 6.9 diesel with 1, 2 , and under drive i was wondering if a transmission with overdrive can be put in and if so will a4od be a better option if at all verses e4od which i have one out of a 91 f250 although that was just a 5.0 motor {probably wont work} ?

 

If your tranny is mechanically sound, and Ur just lookin for od, U could look for a divorced overdrive unit to install in between the transfer case and the rear axel. It's easyer, and depending where you get one and the parts, it could also be cheaper. I had one on my 2wd Chevy 383 hot rod c10. It had a t400 and 4:10s, and once I was on the hwy I just flipped a switch and bam... Went from 4000 rpm at 85 to 2900, and gas mileage went from 8 to 9 . Seriously tho, you can find one for cheep, and even use it as a gear split if your hauling heavy and shift manually.