Bible 8hp70 transmission swap the world

I have a question for you guys that are smarter than me.

I have only done this type of swap stuff with 3.0 to 3.4 Toyotas. Taking an auto 3.4 ECM and making it 5 speed a few times. Not having those trans wires hooked up because there is now a 5 speed would trigger a check engine light. Solution for me was to source a 5 speed ECM and then repin the factory harness because they use most of the same wires of course but just in different places and with different molex plugs.

As I consider this swap for my camper van (2003 E350, 5.4) I was thinking today that without the 4R100 in there, the ecm in probably going to throw codes. That is a no-go for getting it smogged. Of course, there is no 5 speed alternative ECM like my Toyotas.

Am I ****ed and just up thinking about this?
 
dntsdad said:
I have a question for you guys that are smarter than me.

I have only done this type of swap stuff with 3.0 to 3.4 Toyotas. Taking an auto 3.4 ECM and making it 5 speed a few times. Not having those trans wires hooked up because there is now a 5 speed would trigger a check engine light. Solution for me was to source a 5 speed ECM and then repin the factory harness because they use most of the same wires of course but just in different places and with different molex plugs.

As I consider this swap for my camper van (2003 E350, 5.4) I was thinking today that without the 4R100 in there, the ecm in probably going to throw codes. That is a no-go for getting it smogged. Of course, there is no 5 speed alternative ECM like my Toyotas.

Am I ****ed and just up thinking about this?
Click to expand...

5 speed f150 or superduty ecm?
 
Thought about that but not sure if a smog guy would flag it when it comes up as a truck.

Not really sure how that works when the inspection is happening
 
Yeah smog might be hard if your vehicles don't live in a non-smog county unfortunately. There's always the option to get it refereed, but I've never tried and I'm not sure if using an aftermarket transmission computer makes that more difficult. I would hope that just having the factory engine, ECM, and emissions would be enough to satisfy a referee, but the rules probably aren't written that way.
 
The rules are not written that way. Engines have to smog with their factory trans. Your no smoging an engine, your smoging a drivetrain. You can change to one of the other transmissions offered with that engine that year in that application, but you can't go outside of that without going to the ref. So if they offered a manual trans you could swap to that, but then you have to make sure there are no check engine lights on and all the monitors pass. Vin in the ecu has to match what you are actually smoging. They wrote the laws to encourage you to just give up and buy a new vehicle. Thats there whole goal in life.
 
yeah, I have been through the referee here 4 times for 3.4 swaps and always an adventure. They aren't there to help.

I was reading last night about flashing the PCM to remove the auto trans features. This is a pretty popular route for Mustang guys apparently but still can't figure out how that would work for a vehicle that never had a manual option as far as smog inspection goes. I don't think it would. Gonna keep looking into the flash PCM route and see what kind of shady **** I can think of but not looking promising on the horizon. Bummer because this would be ideal for me.

I wonder if that Montana registration **** still works!? :lmao:

Anyways, I don't want to clog up the Bible thread on this more. Thanks for the replies
 
Ok version 3 of the harness, the final version…I swear. It’s even wrapped in fabric tape now. But leading up to this, I made two more mistakes. First, I forgot about activating my reverse lights entirely, d’oh. Problem is the 8 pin connector to the chassis was already full (answered later).

So the next mistake I made, the MaxxECU main power needs to be ignition switched. I thought it had the ability to go into a sleep mode, meaning you could run constant power, but nope. And I had it tied to the constant power to the transmission and shifter, which was also a problem - the shifter and transmission need constant power a few seconds before anything else to go through an initial boot procedure before receiving any communications. I had them coming on at the same time as the MaxxECU Mini which is a nono.

So I pulled the main power and ground out of the 8 pin connector, and put them in their own 2 pin connector you see in the top left (in the engine bay). I’ve also decided I’m going to run separate dedicated power and ground from the battery for these two, instead of grabbing them from the original TCM trunk.

And then, I added an ignition switched waterproof relay right there in the same spot, to run the MaxxECU itself. So the shifter and transmission main power will be constant hot all the time like they expect, and the MaxxECU Mini will turn on with the ignition.

Doing all this opened up 2 pins in the main 8 pin connector to the chassis, so I put the reverse light feed on one of those and all is well. It also means I’m currently only using 7 out of 8 pins there between chassis and MaxxECU, but I’m not sure what else I would want

The only bits of planning I have left before actually swapping is getting a length of driveshaft tubing, and building a new transmission mount. At this point, I think I’m just going to make a basic poly mount that will bolt right into my crossmember, but I’d really rather rubber in the long run.

IMG_2794.jpeg
 
So, did we figure out how hard is to swap a 2wd to a 4wd trans?

I am looking at a 2wd 6.4L and 8HP.
 
Grendel said:
So, did we figure out how hard is to swap a 2wd to a 4wd trans?

I am looking at a 2wd 6.4L and 8HP.
Click to expand...
There’s an adapter out there to make a 4wd into a 2wd but I think the only way to go from 2wd to 4wd would be running a divorced case. The trans case is one piece from front to back on the 2wd ones.
 
Rnuovrcj5 said:
There’s an adapter out there to make a 4wd into a 2wd but I think the only way to go from 2wd to 4wd would be running a divorced case. The trans case is one piece from front to back on the 2wd ones.
Click to expand...
So I guess I swap a 4wd one in.
 
Rnuovrcj5 said:
There’s an adapter out there to make a 4wd into a 2wd but I think the only way to go from 2wd to 4wd would be running a divorced case. The trans case is one piece from front to back on the 2wd ones.
Click to expand...

How is that possible?

Also that's too bad, I believe ford and gm started making thier 2 and 4wd transmissions almost exactly the same a long time ago.
 
YotaAtieToo said:
Sorry, I meant how do they make the entire case 1 piece? Just load everything from the front I guess
Click to expand...

Almost all conventional (RWD 4WD) transmissions are assembled/disassembled through the pump cover. The only thing you get from the pan is the VB, a few solenoids and a few bolts holding main components from spinning that come out the front. Other than tail shaft sections unbolting, and some newer bell housings being removable, what other parts of the case are separate pieces?
 
SLOWPOKE693 said:
Almost all conventional (RWD 4WD) transmissions are assembled/disassembled through the pump cover. The only thing you get from the pan is the VB, a few solenoids and a few bolts holding main components from spinning that come out the front. Other than tail shaft sections unbolting, and some newer bell housings being removable, what other parts of the case are separate pieces?
Click to expand...

Fair enough, I just thought a non removable tail housing was wierd, I would have assumed there would be some sort of bearing clip or something back there.
 
AgitatedPancake said:
Definitely valid, that BMW one is probably less weather resistant with that button right on top. I like the jeep ones a lot as well, so I figure everyone will choose whatever works best for their setup. These controllers allow you to set up buttons as shifters too, like if you have a CAN keypad. But I'd rather have some sort of pysical shifter instead of a push button, even if they're functionally the same thing.



It was ~$790 before shipping with a flying lead harness prepinned into the ECU connector. You can save $50 by going with no starting harness, but I wanted the convenience. here's where I bought it:

MINI | "Seems Legit" Garage

And I also got this connector which mates to the transmission, so I can make a tidy little harness between the controller and transmission:

https://www.seemslegitgarage.com/product-page/8hp-connector-kit

They make a bundle with premade standalone harness, but I didn't think that harness was worth the additional ~$400 over the route I chose:

MaxxECU Bundle Deals | Advanced Engine Tuning by Seems Legit Garage


Now there is one bit of ****ery we haven't talked about yet. When you get a transmission, to work with the MaxxECU you either need to have the TCM in the valve body flashed, or flash it yourself. So you either pull the pan, valve body, and pull the TCM from the valve body to send it somewhere, or rent the tool from a place and DIY. I'm going the DIY route, so I'll keep you guys posted on that.

If you go TurboLamik, you actually pull the TCM from the carrier, and solder in a replacement PCB that makes all solenoid control external via the transmission connector. So this is why the TurboLamik gives total utter control over every aspect of the transmission, you're literally eliminating the stock TCM where the MaxxECU talks to the TCM

Here is Seems Legit's flashing service for $200:

https://www.seemslegitgarage.com/product-page/8hp-flashing-service

This is the flash tool rental I'm thinking of going with. $500 up front, $395 returned when they get the tool back so it's a $105 rental:

MaxxECU 8HPxx TCU Programming Flash Tool Rental – ACDP-2 Module Packag



Regarding the total cost, there's definitely some upfront costs to configuring it, but I like that the actual hard parts of the transmission stay unmodified stock form. So after the expense of initial setup, any ole junkyard transmission will work in the future instead of being filled with custom/specialized parts. I bet you could even swap your flashed TCM between units too so even if you replace the transmission in the future, you wouldn't need to reflash again


Here's the mildly sketchy looking flash procedure if you're on a phone:



Here's a computer based one:

Click to expand...


Pancake,
The harness with the standard comes with the wiring and plugs to go to the shifter. I could swear I saw somewhere that an additional shifter wiring harness was needed but I have read so much stuff on this and 10r80 swaps, I may be getting it confused.

Also, WTF is with internal resistor vs without and why do I want one or the other. It just sounds like a good thing but I am not sure.
Screenshot 2026-05-03 170914.png
 
So the 3 options there are just the bare ECU, or the ECU with the connector and pins with no wire, or the ECU with connector fully prewired with ~10 feet of wire connected and unterminated. That's what I and rnuovrcj5 got as starting points so we could build the rest of the harness, and we also separately picked up the transmission connector. One of my other links in that post was to Seems Legit's premade harness option here:

https://www.seemslegitgarage.com/product-page/maxxecu-mini-and-harness-bundle

But even that one doesn't have the final run to actually connect a shifter, because any shifter you get may end up having different connectors so you need to wire the shifter itself in any scenario. I bought my shifter on ebay, and it had the connector with a pigtail I could tap into to finish out the harness (pics earlier in the thread)

This is how the premium MaxxECU Mini option comes with the flying lead harness:

Rnuovrcj5 said:
Parts showing up now. The plugs are supposed to be here later today.
IMG_1891.jpeg
Click to expand...
 
Got my shipping notification from DomiWorks for the engine/trans adapter this morning. Guess I need to step it up on getting my frame rails put back together so I can mount the drivetrain.

Since I’m doing an engine swap at the same time, I’m trying to resist the temptation to to swap the MaxxEcu mini for a Race with the LS harness and have it all integrated instead of multiple computers to run every thing.
 
Rnuovrcj5 said:
Got my shipping notification from DomiWorks for the engine/trans adapter this morning. Guess I need to step it up on getting my frame rails put back together so I can mount the drivetrain.

Since I’m doing an engine swap at the same time, I’m trying to resist the temptation to to swap the MaxxEcu mini for a Race with the LS harness and have it all integrated instead of multiple computers to run every thing.
Click to expand...
Well, that's what I am after, one control PCM/ECU, whatever you want to call it.
 
Grendel said:
Whelp... y'all talked me into it. Just bought a 6.4L Hemi and ZF8 to go into my J truck, along with a Dodge 60 front and a 14B rear.
Click to expand...

Very nice! What vehicle did you end up getting an engine and trans from?

Rnuovrcj5 said:
Got my shipping notification from DomiWorks for the engine/trans adapter this morning. Guess I need to step it up on getting my frame rails put back together so I can mount the drivetrain.

Since I’m doing an engine swap at the same time, I’m trying to resist the temptation to to swap the MaxxEcu mini for a Race with the LS harness and have it all integrated instead of multiple computers to run every thing.
Click to expand...

Considering you're doing both at the same time, I'd be tempted to do the same if I were in your shoes. I may also be tempted by a stock ECM and standalone engine harness, then keep the mini ecu max as a standalone for the transmission, but I don't think that would really end up saving you much or provide any extra value

Grendel said:
Well, that's what I am after, one control PCM/ECU, whatever you want to call it.
Click to expand...

As far as I've researched, I don't think anything except the OEM controller can run your combo just due to lack of software support for 8hp75, so I don't think you have much choice. But if I were ever to put a hemi in my jeep, I'd be tempted by OEM too just because it's clean
 
2024 Ram 2500. Should be 23 spline output.

Anyone feel like cutting down my harness? Happy to pay... :)
 
Grendel said:
Well, that's what I am after, one control PCM/ECU, whatever you want to call it.
Click to expand...
I’m not sure if there’s a way to just run the oem Dodge stuff that you have without extra stuff. My buddy’s stalled project has a harness done by Hotwire with a Sound German trans controller added into it somehow. It’s a long way from being together though so no idea on how well it works.
 
Grendel said:
2024 Ram 2500. Should be 23 spline output.

Anyone feel like cutting down my harness? Happy to pay... :)
Click to expand...
I think the Gen 2 19+ 2500/3500 output is the big 43 spline. The 1500 would still be 23 spline.
 
Grendel said:
2024 Ram 2500. Should be 23 spline output.

Anyone feel like cutting down my harness? Happy to pay... :)
Click to expand...
bigtoy302 said:
I think the Gen 2 19+ 2500/3500 output is the big 43 spline. The 1500 would still be 23 spline.
Click to expand...

From some quick searching I was doing, it seems like those are the 29 spline units you were talking about earlier Grendel. But it sure is confusing knowing how many different versions of "8hp75" seem to exist

Grendel said:
Seems like you can get almost any spline count output:

The 8HP75-LCV 8-speed automatic transmission in the 2024 Ram 3500 with the 6.4L HEMI engine features a 29-spline output shaft.
While other vehicles using the 8HP75 transmission (like the Ram 1500) typically use a 23-spline shaft, the Heavy Duty models (Ram 2500 and 3500) use the larger 29-spline configuration to handle the higher torque loads and weight ratings of the 3/4 and 1-ton chassis

Since I am going with a 6.4L Hemi and 8HP75, I can use either a 23 or 29 spline variant and adapt my Dana 300 to it.
Click to expand...

---------------

Rnuovrcj5 said:
I’m not sure if there’s a way to just run the oem Dodge stuff that you have without extra stuff. My buddy’s stalled project has a harness done by Hotwire with a Sound German trans controller added into it somehow. It’s a long way from being together though so no idea on how well it works.
Click to expand...

Now that's interesting, are the latest generations of ECMs still pretty restricted/locked? I kinda thought the Sound German controller was for integrating the 8hp's into OEM controllers of other brand vehicles, versus actually making the dodge stuff run happy standalone, but I had a hard time finding out the exact niche it's meant for
 
AgitatedPancake said:
From some quick searching I was doing, it seems like those are the 29 spline units you were talking about earlier Grendel. But it sure is confusing knowing how many different versions of "8hp75" seem to exist
Click to expand...
Yeah kinda confusing on the newer gen 2 stuff. I knew it was bigger but wasn't sure. I think some of the Jeep 8hp75's (Hemi 392? ) are the 43 spline then. Makes sense on the 2500/3500 are 29 spline like the older manuals.
 
bigtoy302 said:
Yeah kinda confusing on the newer gen 2 stuff. I knew it was bigger but wasn't sure. I think some of the Jeep 8hp75's (Hemi 392? ) are the 43 spline then. Makes sense on the 2500/3500 are 29 spline like the older manuals.
Click to expand...

That seems right from what I've seen so far - the V8 JL/JT "8hp75" seems to be the 43 spline version with odd tcase pattern. Then google says the Gen 5 Ram 2500 and 3500 gassers seem to have a 29 spline - I'm not sure if that's the regular 6 bolt pattern? Then the Gen 5 Ram 1500s might have a 23 spline round 6 bolt 8hp75? But I'm not confident about all of that, just what I've gathered so far (would absolutely welcome more clarification!)
 
how is the ability to shift to reverse from a higher gear in these? I see sequential shifters are the common aftermarket option, but for our use case I can see myself needing to go from 2nd or 3rd to R very quickly and downshifting 3 times would take too long. Any options for shifters that allow for that like the winters for the TH400 and 4l80s? Or wire a button that when you hit it and downshift it tells to trans to go into Reverse from whaterver gear its in?


Also how picky are these trannies when in manual mode? Will they let you hold a gear regardless of hitting redline in 2nd offroad or will they try to shift?
 
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