I have a 1991 F350 7.3 diesel with the ZF-5 transmission. I also have a 1991 ZF-5 from a 5.8L gas truck. Is it possible to swap the lower-geared internals from the gas version into the diesel case?

It seems like this would be an easy way to get lower gearing in the diesel and still keep the higher axle gears for freeway speed. This is for a daily driver.

Also, I asked this in another thread but I'm wondering what it takes to swap out the BW1356 for an NP205 or an NP203-205 doubler. I'm familiar with the doubler, just not the swap from BW1356 to NP.

Thanks

the t case swap is pretty easy just some grinding to clear the shifter rail. as far as swaping internal it is possible but is quite involved and not really worth it imo.

Thanks for the info. I'll look for something more practical than swapping gears between the ZF-5 cases.

What kind of clearancing is required to attach the older transfer cases to the ZF? I'm specifically asking about the married NP205 as I have one sitting here, but a future doubler sounds good too.

Thanks again.

the rear housing will just need a small notch cut into it to clear the one shift rail on the 205 real simple and real obvious once you get it going into the truck.

Thanks!

IMHO, just building a 13-56/205 doubler, rather than swapping in a 203/205 setup is easier, cheaper, and a better setup(as far as ratios go)

Why do you need a lower gear for the diesel? For a DD. I have no idea why youd want such a low gear for first, unless you haul a really heavy load.

Anyways, I would talk to a guy who builds manual transmissions, esp. one who is in a shop that can show you the case of both transmissions, and confirm why it will or won't work. My initial guess would be that the design of the diesel version was to allow it to handle more torque than the gasser, and the gasser having the lower gear to make up for the lesser amount of off idle torque of the gasser..

I'm interested in the doubler 1356/205. I have found a few threads that seem to be experimental attempts, but not anything that looks mature. I'd appreciate any pointers or links to more info.

I'm sure I don't "need" such low gears but I'd like to have some. I'd like to run taller tires to bring the highway RPM down, but still maintain or improve the low end.

I guess my situation is unusual. My commute is only to the airport 10 miles away. Most of my miles driven in this truck are in 100 mile nonstop bursts several times a month. I think I have put on about 2500 miles in 5 months.

I run 4wd pretty often on each end and all freeway in the middle.

I'm also collecting parts for a trail buggy and the 7.3L diesel is one of the engines I'm considering. I'm sure an SBC would be cheaper and easier but I want to ask the questions first...

I guess I spoke too soon.

Jrod, are you still running a 13-56/205 doubler? I'd appreciate any pointers or links to a how-to that will get me on the right track. Of course if 2.7 x 2.0 is good, what about 2.7 x 2.7? 13-56/13-56 doubler?

I currently have the 13-56 in my truck and another in a parts truck. I also have a Ford married NP205 and a couple of Ford divorced NP205 for parts.

Plenty of parts to build either kind of doubler. I don't have a machine shop but I do have all the normal saws and grinders.

I appreciate any guidance. :)