Hi,
my father has a F250 2wd 1991 with the 7.3L diesel engine which suffers from a leaking automatic transmission. It was bought like that with the intention to rebuild the transmission as we have a friend that do that professionally, however we also got a 4wd transmission (automatic + transfer case) in good shape with it.

The idea just came up that it might be possible to use the 4wd transmission, maybe temporarily while the 2wd transmission is rebuilt or permanently if it works fine. Googling on the subject (2wd to 4wd conversions) I found a lot of information and found that it was easier than I thought, that a 4wd conversion is a completly bolt on operation.

First things first, what is needed to do to use the 4wd transmission? At first I thought that a different cross member for the tranny mounts would be needed but none of the forum threads I've been reading mention anything about that. So is it the same cross member on 2wd as on 4wd? Any adapter or different tranny mounts needed? Sure, the rear drive shaft will need to be changed or shortened but that's obvious.

While I started seeking information only about using the 4wd transmission and how much work that would be a full 4wd conversion might be intresting when there is some spare time (like if that ever happens!). My father runs a farm and a trucking company so 4wd is useful to be able to drive on muddy fields and snowy roads but we are not looking for something to do any serious offroading (we have tractors for that). In the early 90's he had a F250 4wd that was lifted and with 33" tires, which was cool to look at and fun to drive but as much as it was lifted that much you had to lift anything extra all the stuff that you wanted to load on the pickup bed so we would really not want to lift it anything more than neccesary for the 4wd conversion.

While we certaily have the knowledge and equipment also for serious modifications which require welding etc, I just know there isn't time for that kind of stuff so a bolt on operation is definitly attractive. Another factor is that we don't want to add on unnecesarily weight as the operating weight including driver and full tank needs to stay below 3 metric tons as otherwise it will need to be registered as a heavy truck with our legislation (we have drivers license for that too but others that might need to drive it do not). I believe the TTB is lighter than a dana 60 solid axel so that would definitly be preferable. The 4wd we had earlier was 100 kg or so over the limit so it had to be registered as a heavy truck..

Looking at parts for the conversion I find that (obviously) the F250 has a different front axel (dana 50) than the F150/Bronco (dana 44). It's easier to find parts here for the latter, I know of a 89 Bronco which is being scrapped for parts but as I understand those parts would not be usable even if the diff/drive shafts are changed?

The F250 is more rare, but possible to find parts. Which years would have compatible parts, only 87-91 or also 92-96?

As mentioned earlier the short term target is just to use the 4wd transmission but as it seems to be relatively easy to do a 4wd conversion that would be something we would start looking for parts for.

 

Swapping a 4wd axle under the truck will be a bit more involved than you think, the frame mounts for a TTB are different than those for a 2wd setup and those pieces are riveted on. Also I'm also not sure a light duty D44 would fit the F250 frame and even if it did you would then have 5-bolt 15' wheels on the front and 8-bolt 16" rims on the back, and the wheel spindles are not interchangable between the D44 and D44HD so there's no shortcut there either. Bottom line is you probably need a complete 4wd F250-F350 donor vehicle to complete this swap correctly.

 

Well, thats why I wrote "relatively" easy. Of course there is work involved and for the average sunday driver it would be a difficult task but none of what I've read so far regarding a swap makes me any worried. We are used to work on repairing tractors, trucks and other farming machinery, it's just that I know that if the conversion would involve much work it will not get done but if it can be done in 1-2 days (as many forum posts I've read indicate but always count in a few extra days for the unforseen) then there is a very good chance it will be completed.

Preparation is everything though. In short term I want to find out if there are any major obsticles to use the 4wd transmission as an intermediate step, then planning for the long term goal would be to do the complete 4wd conversion.

The D44 from F150/Bronco will not fit, I've found that out now at least, which doesn't come as a supprise. A donor F250 might be possible to find, they are very rare over here (Sweden), but not impossible to find. The mounting brackets that are riveted on from factory can be found as bolt-on replacement parts, we already had to change some of the brackets for the rear suspension and it was a piece of cake (30 min work with the blow torch and a lot of curses to remove the old bracket, then less than 10 min to get the new one in place and assembled).

Anyone have diagrams of the TTB?

 

It will be eaiser to put a Dana 60 or Dana 44HD under the F250. If you just want to keep it 2wd you can swap the output shafts between the two transmissions. (However to do this you will have to completely tear down both trans, and need a seal kit for the one you're putting back under the F250.)

Whats size tires are you running now? Most 4x4 F250's I have seen have enought lift from the factory for 36's.

 

It was a previous F250 that we had back in the 90's which was 4wd and lifted, I don't know how much and my previous estimate on tire size was probably a bit low. What I do recall is that the bottom of the door was at the height of my hip and I'm 2 m tall so that makes it roughly 1 m over the ground. However, that's a side track. The 2wd that is the target for the maybe to be conversion has stock size tires.

Anyway, I've googled extensively on the subject during this evening and found that there are basically 3 alternatives:

1. Use D44 TTB axle from F150/Bronco, which turned out to acctually be possible. This is the easiest alternative, it fits the same mounting points as the TIB axle of the 2wd, the same suspension etc. The biggest difference is that the 4wd have double shock dampers so the upper mount for those is a bit different. To get 8 bolt the knuckles from a chevy D44 can be used. Parts for this approach is easier to find but the main drawback of this approach is that it will not be as strong as a D50 or D60, we will not do any serious offroading but I still don't like the idea..

2. Use a D50 or D44HD TTB axle, they both seem to have the same mounting brackets. The pivot bracket on the engine crossmember is different than the 2wd mount but it's a bolt-on piece. The F250 4wd use leaf springs so brackets for that needs to be added, the frame might need to be boxed where the brackets are placed but I'd check that on a 4wd frame. The rear end needs to get lifted some to get to the same level as the front. This is the approach which is closest to the stock 4wd.

3. Use a D60 solid axle. This conversion also use leaf springs so that part is the same as no 2. A sway bar (is that the right word?) bracket needs to be bolted on the crossmember. The main drawback with this approach is that more lift is needed for it to clear the engine crossmember. The main benefit would be that the alignment issues with TTB is avoided.

There are definitly challenges with any of the approaches, I'll keep an eye out to see what parts I can find...

 

As for using the 4-wheel drive transmission while in terms of "in progress", you can, and wont have any issues.

You will need to however, either get a 4-wheel drive model rear driveline to swap out, or get your driveline cut and balanced to fit.

 

Midwest, thanks for confirming