Will a 96 f350 e4od work in a 91 f350?

 

Sure, as long as the '91 F-350 has the same engine, and both are 4x4 or both are 4x2.

 

So long as it came from behind the powerstroke,it will bolt to your idi. You could use a 4wd version too if you have a 2wd truck but you would need to add a t-case and a shorter driveshaft of course.That would give you a set of low range gears to use for crawling around.I always thought all trucks should come with 4wd trans and t-cases regardless if they have a front drive axle or not.It's always nice to back up trailers and such in low range and great for many other things.

Anyway,you can use the PSD trans behind your IDI but you'll need to swap solenoid packs (you can just re-use your old one so long as it's good) and you'll need the 4 stud diesel converter as the PSD uses a 6 stud and this should be replaced with a reman during the swap.I wouldn't re-use your old one.

Don't forget the speedometer changover year. I think with your '91 your ok? I always forget this and I always say I always forget this lol! But if your old E4OD uses a drive gear in the trans (2wd trucks) then your stuck using a older trans with it OR adding the t-case as mentioned as those older 4wd trucks had the speedo in their t-cases.
I think I got everything covered you'd need to keep in mind.Next time be sure to be more specific on your truck and the donor as it can save us some time guessing some stuff.Little did you know though how loaded your question was when you asked it I'm sure.

Pusu' Puna'ne - Happy New Year!