Wee let me start with I'm new to this section of the forum and would like to become a permenent member of this section. Now lets get to buisness, Im looking at getting a 1985 f250 4x4 extended cab. She has the 6.9 diesel with an ATS turbo set up, ARP head studs and victor reinz gaskets, but the transmission is a 3 speed C6. I know the tranny can handle the power this engine puts out. but I was wondering if I could take this tranny and swap in a ZF5 out of a newer diesel. My dad has talked about guys that have swapped the 6.9 out for the 7.3 because its a direct bolt in swap. It's not that big of a deal if I have to modify the crossmember because I have the tools to do that. I know it would be a pretty large job but it would be badass to have a 6.9 turbo bull nose with a 5 speed instead of a 4 speed. Please Let me know what you think!! I want any and every possible pros and cons of this swap and personal opinions. So start lettin me know what ya think!!!

 

Very doable.

I used a 7.3/ZF5 out of a 89 to go in place of a 460/C6 in mine.
I retained the stock BW1345 transfer case.

You'll need the trans, flywheel/clutch, trans cross member, and the pan that bolts onto the transmission tunnel (where the shifter goes through the floor).

The ZF5 crossmember bolts on to the same location on the upper 4 bolts, the 2 bolts that go through the bottom of the frame rail are off by about 1/2" so you have to drill 2 new holes.

I had to trim about 1" off of the front of the shield underneath the transfer case for the crossmember to clear it; if you got one out of a ZF equipped truck it should bolt on and clear fine.

I used the transfer case shifter/linkage out of the 89; it's the version that has it's own hole through the floor just to the left of the pan the shifter goes through. So I had to chop a hole in the floor for it.The newer Bw1356 has a different setup, so I had to shorten one of the links for it to bolt up to the BW1345.

And I didn't have to change the length of any of the drive shafts.