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Parts list for 3.9-5.9 swap

101K views 64 replies 34 participants last post by  GreenTrok 
#1 · (Edited by Moderator)
Just like the title says I wanna know what I'm gonna need to swap from a 3.9to a 5.9. obv I need the motor but I'm not sure what else the computer/wiring harness/trans/rear end/motor mounts are. figured I should see what I need so I can start getting things together. sorry if this has been asked/answered before didn't think to search til now and I already have all this typed it would be a waste to delete it :funny: thanks!🙇
 
#2 ·
for a complete swap of need, 360, 5.9 matching year ecu, engine harness, 46re, 9 1/4 rear end, basically what a r/t has, now if ya just wanna swap the motor then the all ya need is a 5.9, 5.9 ecu matching the yr of your dak, and engine harness. the 42re and 44re will work but over time and abuse theyll give out depending on the amount of abuse and power the motor is producing is how long theyll last.
 
#3 ·
You'll also need a V8 fan shroud if you're using the clutch fan... The V6 one is too big. And even if you were going with a Viper electric fan, I'ld get the V8 shroud.... looks a lot cleaner.

You don't really need a 9.25 rear end, an 8.25 would work. If you keep the 8.25 you might need a slip yoke so you'll driveshaft will go into the transmission or if you swap the rear end, you'll just need another driveshaft.
 
#4 ·
Nothing wrong with a 42re/rh behind a 360. Don't let people fool you, I have one, I beat the shit out of it 95% of the time. It has held up for 2 years so far, knock on wood.
 
#6 · (Edited)
Been down this road already - search for my 3.9 to 5.9 swap thread, it has EVERYTHING you need to know.

You need the engine from anything, and a PCM from a truck which is the same year as yours. That's extremely important. Engine doesn't care what it's in - as long as it's relatively new and low miles, you don't have to worry about compatability. If it's from a Ram, you'll need a Dakota oil pan.

That's IT.

42RE is fine behind the 5.9. A lot of people on this board talk about things that they have no experience with - they are just talking shit. Let them talk. Don't buy a new transmission. Get yourself a big trans cooler and don't worry about it. As the other guy said, I've had my 5.9 behind my 42RE for almost 40,000 miles and I race every weekend and street race at least once almost every day, and it hasn't shown any signs of starting to slip.

A few things you will need to modify:

-Your wiring harness. You will either need to get a harness for the 5.9, or modify your 3.9. IIRC, one of the sensors needs to be lengthened, and you need to wire up 2 injectors (easy as pie).

-Radiator hoses and heater hoses. They will be too short. Either get the right hoses, or get some clamps and extensions and extend them. I just extended what I had, and it's worked perfectly

-Your fan shroud. You definitely don't need a new one - If you look down into your engine compartment, you'll see the top of your fan shroud, then a big circle sticking out a few inches towards your engine. Take a sawzall and lop off that circle, and the 5.9 fits perfectly.

-One of your motor mounts. I forget which side it was, but if you use the mounts from your 3.9 (do it, save money), you will have to grind down a little bit off of one of the corners. You won't be able to bolt it to the engine - the corner of the mount will hit the block ever so slightly. Just grind it down until it fits like a glove.


Fuck the 9.25 rear end - Unless you plan on having a power adder, your 5.9 won't have enough torque to come anywhere close to harming your 8.25. If you're nuts like me, and decide to put 4.56's in the rear end, you aren't going to be able to keep your tires planted anyway :drive:

You don't need a new slip yoke. Not sure where that one came from or why the hell he said it. The back of your engine will be in the same spot as your 3.9, it will just come a few inches farther forward in the front where the 2 extra cylinders are. Thus, your transmission stays in the exact same location, and your slip yoke will rest in the same fine position as it was.

If for some reason, you feel the need to get a new transmission that is a different length then your 42RE (I don't know the dimensions, so if the 44 or 46 are shorter), then you will either need a new driveshaft or a longer slip yoke. That would be a huge problem - TRUST me, I learned that lesson in my Mustang. You need the slip yoke to slide fully onto the output shaft of your transmission. It needs to have a certain amount of that yoke on the output shaft, otherwise it doesn't function properly. There's a possiblity of the teeth on the gears stripping, but the bigger worry is rotation of the driveshaft. The U-joint is designed to allow the driveshaft and output shaft to rotate at different angles.. but it's still precise. If the driveshaft end orbits out of its axis of symmetry, your output shaft orbits as well, and so do the internals of your trans.. tears up the inside, governor bore hogs out the case, etc, and you can kiss your brand new transmission goodbye.

My advice: Keep your 42RE, get your hands on a low miles 5.9 out of a Dakota or a Ram, get yourself a PCM from a Ram of the same year as your truck (they have better PCMs then the Dakotas), drop it all in and fire it up. It's about as easy as engine swaps get. If you have any questions, drop me a PM and i'll help you.

Here's my V8. Take note of the way I fixed the radiator hoses and heater hoses, as well as the fan shroud modification.





You're going to be a happy camper the first time you drive your truck after the swap LOL. Man, that was a good day.

More pics, just because I love my cars. Here's my Mustang. She's sold now, unfortunately. I built that bitch from the ground up. Engine, trans, interior, body, suspension, EVERYTHING. Took me an entire summer, but it was worth it. Then school rolled up and said 'hey pay us tuition' so I had to sell her :(







And, just for shits and giggles, here's a picture of what my slip yoke looked like before my Uncle looked at it and informed me that it would be extremely bad to try and drive a car with any amount of power using that setup LOL. Hey man, I'm human too. Everyone makes mistakes - learn from them!



^^That's what you DONT want it to look like. Here's how I fixed the situation - I'd recommend that if you have the same problem, you get one of these bitches:



Lightweight aluminum racing driveshaft. Brand new U-joints and slip yoke, Custom made to the exact length I needed and balanced perfectly. Doesn't get better then that.
 
#12 ·
5.9 = 5.9. Only significant difference is the oil pan. As long as it has >80K miles, it will be out of something new enough that everything will work. Durango PCM won't work.

Your ABS will also never work again after the swap. You don't need it, though. I was worried about it for a while after I did mine - but I've been in several situations where I needed to rapidly decelerate on the highway, and I drove for an entire rough Michigan winter, and never even noticed the difference.
 
#17 ·
i may hav found a motor/tranny combo for a good price. only thing is they are still hooked together. tranny was rebuilt and has 2K miles since the rebuild so it should together for awhile right? also is it possible to do the swap with the engine/tranny connected? (all out of a dakota r/t)
 
#28 ·
Same here !

I'm putting a 5.9 from a wrecked 99 Durango, in my 99 Ram 1500 base with the 3.9 5 speed. I have the PCM from the donor vehicle, but it was an automatic so I'm not sure if it will work. Anyone have any info on this ? I'm also not sure if one of my ac hoses will be long enough. I bought a new flywheel that is supposed to be balanced for the 5.9, and everything I've read says that while the nv3500 isn't the ideal tranny, it should hold up fine under normal use. Again, anyone been down this road ? Thanks
 
#31 ·
Yeah Baby

I finished my swap a week ago. I just spliced in the #7 & #8 injectors , which turned out to be easy , had a PCM programed by an outfit in Miami , and also a bigger radiator. I have all the same gauges and everything works as it should. The payoff comes when you get behind the wheel , huge difference between the 3.9 and the 5.9. It is well worth doing , and not as difficult as you might think.
 
#32 ·
I finished my swap a week ago. I just spliced in the #7 & #8 injectors , which turned out to be easy , had a PCM programed by an outfit in Miami , and also a bigger radiator. I have all the same gauges and everything works as it should. The payoff comes when you get behind the wheel , huge difference between the 3.9 and the 5.9. It is well worth doing , and not as difficult as you might think.
So what did your swap cost to include the exhaust?
 
#34 ·
So you can use the V6 gauge cluster?

What about the V6's fuel pump?

And when it comes to splicing in the injectors, can someone please elaborate on this? I plan to swap my 3.9 to 5.9 this summer, so i would like all the info i can get.
 
#35 ·
And another thing..I've seen/heard about Security/Non-Security PCM's..Which one do you want? My truck is a 98 CC 3.9 auto, and it has a factory alarm, which will flash " Security" in red on the cluster when you lock the doors and close them..So, my current PCM is a security one? So I'd need a 98 R/T Security PCM?
 
#37 ·
Simple.... Autotrader or Craigslist..LOL... Nah its not that bad... 2000 models suck if you're one like me wanting to keep your 5 speed! Still working the bugs out!
 
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