3L80 to 4L80E Transmission Swap

I have a 1994 M998A1 with a 6.2L NA and I am looking to start the big project of swapping the 3L80 for the 4L80. I've started my initial research and saw some discussion on the list of things that need to be done and it is quite long, but some were saying that its better to upgrade to a 6.5l and then its easier to swap the transmissions. That way is too pricey for me. So my question is, how easy is it to swap these transmissions on a vehicle like mine? And would any 4L80E humvee transmissions work? Links to where to get these things would be much appreciated.

I would send Retired War Horse a PM. He is in the business of doing the upgrade.
I did mine a while back but it was at the same time I did the upgrade to the 6.5NA.

First off what is your goal.
Why are you doing the upgrade?
Is it just to get park? You can install a park pawl in the 3l80 without to much work.
Or is it for the overdrive?
What transfer case do you have 218? 242?
most likely if you have a 6.2 you still have a 218 transfer case

How long have you owned the vehicle?
How much do you drive it?
Where do you live?
is it stored inside?
Can you work on it inside?

If you haven't owned it long you may find the novelty of owning one is way overrated.
If you like tinkering on mechanical things allot then congratulations you bought one of the most maintenance intensive mechanical things out there.

Ok
The 4l80 will require some kind of transmission controller because it is electronic.
You can choose an aftermarket controller or the military one.
After market around $400-$600 and no need to change harness.

If you want to use the factory or military one the main body wiring harness needs to be replaced.
new there around $1,000.00
Then you need the military controller on top of that.
Then the relay and breaker and panel they mount too as well as a new brake switch.

No matter what you need a new shifter.


The 4l80E / 242 T case is longer then the 3L80/ 218T case so yes your going to have to modify your drive shafts accordingly.
What front and rear diff's are you running ?
You may have to change out the yokes on them if your not also planning on changing them out .
The upgraded 6.5 242 T case combo uses a different length drive shafts and larger yokes and U joints
Does your HMMWV have the upgraded parking brakes ?
Or do you still use the drive shaft parking break?

Fuel tank mod?

If funding is limited then you need to decide just how much money you want to throw at it and what your hoping to gain from it.
If you don't do it right from the beginning your just kind of wasting money in my opinion.
I drove mine for about 4-5 years using an aftermarket controller. Then I went all in and pulled the body off .
At that time I changed to the factory 6.5 NA 4l80E harness and controller.
I only worked on it on weekends and it was apart for 7 months.
But I basically changed everything to A2 parts while I was at it. And insulated the whole tunnel area .

RWH says you can replace the wiring harness without separating the body from the frame and I believe him but he has more patience then I do.
What ever you decide don't cut corners in the process .
Good luck
BH

My whole goal is to get the overdrive. It seems like there are many routes to take and the one I'm looking for is the cheapest least modification intensive route. I have limited access to equipment to do the job so if there are people who can do the actual swap (around Washington state) then a reference would be much appreciated (I don't have a small crane). As for the use it will get, I frequently put several hundred miles on it per week, give or take.

So what will I have to do that is cheapest and not as much replacing everything in the drivetrain.

I think but can't be sure that you will need some kind of adapter to mate the 4l80E trans to the 6.2 engine. Again I would PM Retired War Horse on this forum as well as the G.503 forum or Ted Gates.
Retired War Horse is in Northern Calif.

The G503 forum has a nice HMMWV section you may also what to check that out in search of info.

The 4L80E will bolt directly to the 6.2. The flexplate can even still be used, but because they do crack and they are under $100 I would install a new one while the trans is off. The same flex plate is used on both the 6.2 and 6.5. Unless you replace the timing chain and sprockets to one from a 6.5 and also at that same time install a 6.5 timing cover casting, you won't be able to install the engine rpm sensor that is used with the pure military wire harness setup. You can take the quick and easy path and use an after market trans controller from TCI or MSD. They are only about $600, but you may end up going to the dark side from which there may be no return!

erasedhammer.....which ever way you go, you still need to change at least 2 driveshafts [ middle and rear ] and rear diff. yoke.
Trans X member also.

dilvoy said:

The 4L80E will bolt directly to the 6.2. The flexplate can even still be used, but because they do crack and they are under $100 I would install a new one while the trans is off. The same flex plate is used on both the 6.2 and 6.5. Unless you replace the timing chain and sprockets to one from a 6.5 and also at that same time install a 6.5 timing cover casting, you won't be able to install the engine rpm sensor that is used with the pure military wire harness setup. You can take the quick and easy path and use an after market trans controller from TCI or MSD. They are only about $600, but you may end up going to the dark side from which there may be no return!

Click to expand...

What do you mean by dark side?


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I recently installed a 4L80E into my M1028A with no difficulties- things that required changes were-
lengthen the front drive shaft by 1+1/2 inches
shorten the rear drive shaft by 1+1/2 inches
re position the frame mounted shifting lever
adjust the cooling lines
drill new holes for the rear cross member
adjust the housing on the transfer case mounting bracket
I used the TCI controller
only problem I have left to solve is that I used the tach pick up off of one of the alternators and the TCI controller reads that info as 12,000 rpm when cruising at 65 mph so I will be mounting a trigger on my crankshaft.
It was a really easy swap to do and now I enjoy keeping up with most of the traffic in encounter.
Please keep us updated on your journey to overdrive - have you considered the Gear Vender option? That is a unit that bolts up to the out put shaft side
of your final drive that creates overdrive only to your rear drive shaft- I must say between purchasing a transmission you know is reconditioned, purchasing a controller and doing shaft work on both drive shafts this is the easiest and cheapest route.

best regards- pete

Pete, what was your final costs if you don't mind me asking.

DCIV said:

Pete, what was your final costs if you don't mind me asking.

Click to expand...

Enquiring minds want to know. I need this so I can put it in the 2018 budget.


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DCIV said:

Pete, what was your final costs if you don't mind me asking.

Click to expand...

PM sent

Dock Rocker said:

Enquiring minds want to know. I need this so I can put it in the 2018 budget.


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Click to expand...

here you guys go!
bought a freshly rebuilt trans that had 1000 miles on it for $600,
TCI controller for $550
TCI - TSP for $150
drive shaft work $310
since I was too much to do this in my drive way I paid a guy who has a shop with a lift and all the cool guy tools $800 - he let me help and it took us about 15 hours to complete the task.
total was $2410
the Gear vender option was initially high but became very reasonable as my project when further down the road and would be something I could do in an afternoon at home. Only down fall would be no overdrive in 4 wheel.
All things considered I am very happy with the results. I was initially thinking of getting all the OEM controller stuff from a salvage yard but thought better to get new electronics
.
I had one other item come up- with the new trans in place I developed a vibration in the driveline @ 58 - 62 mph- I adjusted the drive line angle down about 1+1/4 inches- utilizing the mounting bolt spacers that were initially above the frame where the rear cross member mounts to be between the frame and cross member which remedied the vibration- I do not see anyone lese who did the same swap have the same problem which makes me think I need to check my engine mounts.

let me know if you have any other questions- happy to help.

I forgot one other thing in the line of costs - $50 to a machine shop to make the adapter plate accept the new trans-
pete

So I found the gear reduction webpage, called tech support, they said call the owner nick....nick said he can't help me as there isn't room and the awd. He wishes me luck with a trans swap. Lol.

............
let me know if you have any other questions- happy to help.

I forgot one other thing in the line of costs - $50 to a machine shop to make the adapter plate accept the new trans-
pete

Click to expand...

Why wouldnt the 4l80e bolt to your motor?

Action said:

Why wouldnt the 4l80e bolt to your motor?

Click to expand...

Yes, the 4L80E did bolt right up to the 6.2- however the M1028A is equipped with a NP205 transfer case, part of the adapter plate is the front portion of the case and has a slightly larger locating ring where it mounts to the transmission- bolt pattern is the same, the ring is about 1/16 th of an inch too large which I had to cut down to make everything bolt together tight.
The item that needed to be adjusted goes between the trans and the transfer case.
Man, I forgot one other item- I also had to cut off the 4 wheel shift lever off of it's bracket and move it about 2 inches forward since the transfer case was moved towards the rear because the 4L80E is longer

That's all that was needed and I am now keeping up with some of the expressway traffic- and sometimes passing!!!! I am truly in the 21 st century!

I guess that is what threw me off. I thought you meant to type m1026, not m1028 in this HMMWV forum.

trans

Performance automotive transmission center. Direct bolt in, no cut drive shafts, cross member is fine and no computer. I'm installing one in a customers truck next week. Will have park and overdrive. I'll post how it turns out.

infidel got me said:

Performance automotive transmission center. Direct bolt in, no cut drive shafts, cross member is fine and no computer. I'm installing one in a customers truck next week. Will have park and overdrive. I'll post how it turns out.

Click to expand...

A 4l80E with no computer? Either it’s 700r4 which if not properly built is a dog not worthy of a chevette or it’s a full manual valve body kit and would be a nightmare to drive.

I tried a full manual TH400 and it lasted about two weeks or street driving. Even with a good ratchet shifter it was tiring to shift up and down after every stop and start. I couldn’t imagine adding another gear to that plus torque converter lockup. That would be like driving a Rubicks cube.


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Go to their web site

That is quite possibly the worst website in modern history. I couldn’t find anything about a hmmwv.

Good luck with the swap. Let us know how it goes.


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