I have a 98 Expedition 4x4 with a 4R70 and the transmission seems to have seen its better days. I got the truck a couple weeks ago and drove it 1,000 miles south to FL. I loaded the truck full of crap, plus a 2,000lb trailer and about 3,500lb worth of Cobra on it. With it packed to hell I drove it 1,400 miles back north and the little 4.6 didnt handle that well at all and neither did the transmission.

Since that trip I cant get the 4x4 to work correctly and the OD light flashes shortly after I start driving it. I have 3 parts on the way to try to fix the 4x4 problem but it shutters like the TC or the overdrive valve is having problems.

I have a build planned later down the road and a 4R100 seems to be the stronger of the two and it'll work with my project easier as well. So I want to know if I can just switch the 4R100 for now without running into alot of problems?

 

Not knowing how old the fluid or filter are, I'd start with changing those to see if the problem is a simple one.

 

It depends what you mean by a lot of problems. You can switch them, a 4R100 with the modular bolt pattern will bolt to the engine. The 4R100 is longer than the 4R70W, so you'll need to shorten the rear driveshaft and lengthen the front.

Now comes the fun part! The computer and wiring that are in the truck won't work. Ford never built a 4.6L/4R100 combination so that computer doesn't exist. You may have to go aftermarket with either Baumann or PCS. I understand both of them make stand alone transmission controllers. You might be able to get a 5.4L/4R100 computer to work. The harness will have to be replaced or modified because they are different.

 

I would do something like that but my build plans for later call for a 4R100 to simplify any computer issues so I thought if I could figure the trans stuff out now then the rest would be easier down the road. Atleast that was what I was hoping for.

The computer and the wiring harness will get changed for the build from a donor truck. I might end up running two ECUs in parallel to keep from rewiring the entire interior of the truck.

I was told that Ford did do a 5.4/4R100 option in my model year truck with the 4R100 being optional so Im hoping to find factory parts and transfer them over.

The connectors and/or locations different from the 4R70 to the 4R100? Would a modified harness work? How about if I replace the trans harness with one for a 4R100 and attempt to plug it into the factory location?

 

If you have a donor truck for the parts you might just swap the engine and transmission at the same time using the wiring and all of the other parts that you need from the donor. You definately do not want to buy a wire harness from Ford for that truck as they are very expensive, if you can find one.

 

I don't think that will work. If the ECU isn't running the engine it isn't going to have the information to run the transmission.

It wasn't optional, it was a flex application. Ford would switch between the two transmissions depending on how many of each transmission the transmission plant could build and how many trucks were ordered. The customer had no choice over which transmission the truck was built with. Having said all that, factory parts should be available to swap.

The connectors are different. I don't know if the pin locations at the PCM are the same or not. I could modify one harness to work on the other, so it could be done.