6.5NA HMMWV 3L80 to 4L80e

bcox11

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Oklahoma
Let me start by apologizing if this subject has already been posted before. I bought an ‘89 M998 in September. I had a 6.5L NA engine, 3L80 Trans, and a 242 T/C. Everything has been fine with it until a few days ago. Started having trouble shifting up. Also, it was downshifting. I drained the trans fluid and dropped the pan. Found quite a few teeth in the pan. I had already thought about swapping the 3L80 to a 4L80e some day, but not this soon. Now I don’t have a choice. Since I have to rebuild or replace the trans, I’d like to go with a 4L80e. A lot of the threads I’ve read talk about people that have a 6.2NA with 3L80 wanting to swap to a 4L80e. But, I have the 6.5NA. Can anyone help me figure out anything and everything that I’ll need? I greatly appreciate any help.
 

BLK HMMWV

Well-known member
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Let me start by apologizing if this subject has already been posted before. I bought an ‘89 M998 in September. I had a 6.5L NA engine, 3L80 Trans, and a 242 T/C. Everything has been fine with it until a few days ago. Started having trouble shifting up. Also, it was downshifting. I drained the trans fluid and dropped the pan. Found quite a few teeth in the pan. I had already thought about swapping the 3L80 to a 4L80e some day, but not this soon. Now I don’t have a choice. Since I have to rebuild or replace the trans, I’d like to go with a 4L80e. A lot of the threads I’ve read talk about people that have a 6.2NA with 3L80 wanting to swap to a 4L80e. But, I have the 6.5NA. Can anyone help me figure out anything and everything that I’ll need? I greatly appreciate any help.
Do you have a dual voltage alternator in it?
What size?

The 4l80e will need a trans controller
You need to decide if your going to try and keep it all original using the military Trans controller or an aftermarket.
Both require 12 volts.
Your 6.5 NA may already have the 200 amp dual voltage alternator on it.
Shifter . the 4l80 will now have a park position as well as an overdrive so you will need to source a shifter.
Wiring harness : if you want to stay with all military you will need a new main body harness or you will need to make one.
If you are going aftermarket then you just need to pick one of the aftermarket controllers.

Not sure if you might need to do anything with your drive shafts since you already had a 6.5 with 242 not sure how much bigger or shorter the 3l80 is from the 4L80E.

The link in the post above should answer a lot
 

bcox11

New member
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1
3
Location
Oklahoma
Do you have a dual voltage alternator in it?
What size?

The 4l80e will need a trans controller
You need to decide if your going to try and keep it all original using the military Trans controller or an aftermarket.
Both require 12 volts.
Your 6.5 NA may already have the 200 amp dual voltage alternator on it.
Shifter . the 4l80 will now have a park position as well as an overdrive so you will need to source a shifter.
Wiring harness : if you want to stay with all military you will need a new main body harness or you will need to make one.
If you are going aftermarket then you just need to pick one of the aftermarket controllers.

Not sure if you might need to do anything with your drive shafts since you already had a 6.5 with 242 not sure how much bigger or shorter the 3l80 is from the 4L80E.

The link in the post above should answer a lot
BLK HMMWV, thanks for the post.


I have a 24 volt alternator at 60 amps. As for the TCU, I am not set on either at the moment. I guess that the deciding factor is money and timeframe. The HMMWV is my daily driver, so I need it fixed quickly, but also need to save money.

As for the shifter, I just ordered the stock 4 speed HMMWV shifter.

Lastly, the driveshafts. That is one of the biggest questions. I believe the overall length will be 2.125” longer if I’m not mistaken.
 

BLK HMMWV

Well-known member
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Pasadena California
You will find member 86humv very helpful when trying to locate parts at a reasonable price.
Some new some used but in good shape.
Sorry got a chuckle out of the "need it fixed quick and also need to save money" part while talking about a HMMWV
 

Coug

Well-known member
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Olympia/WA
You will find member 86humv very helpful when trying to locate parts at a reasonable price.
Some new some used but in good shape.
Sorry got a chuckle out of the "need it fixed quick and also need to save money" part while talking about a HMMWV
Image result for fast good cheap triangle
 

bcox11

New member
5
1
3
Location
Oklahoma
You will find member 86humv very helpful when trying to locate parts at a reasonable price.
Some new some used but in good shape.
Sorry got a chuckle out of the "need it fixed quick and also need to save money" part while talking about a HMMWV
In regard to quick and saving money, I hesitated saying that. Was trying to be honest. I completely understand that there is nothing quick or cheap about HMMWV’s. Normally, I wouldn’t care about time or money, but at the moment my wife and I are buying a house and I’ve already had to come up with several thousands in the last month for part of our down payment. Buying a house sucks, but having your ride go down at the same time is worse.
 
Last edited:

Dayron84

Member
62
12
8
Location
Tennessee
My humvee was converted to 4L80 by previous owner before I purchased it. I have never driven one with a 3 speed trans but I can say it is nice to be able to go down the highway at 60 mph comfortably. I looked at several humvees before buying and this upgrade is why I purchased this particular truck. It can be a fairly expensive upgrade ( especially if your paying someone else to do the work) but well worth it.


Sent from my iPhone using Tapatalk
 

Curtisje

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Twentynine Palms, CA
I think if you carry out your 4L80E upgrade now you will find your HMMWV down longer than expected as you 'discover' more work than expected. When I have found myself in similar situations I tend to cut corners and in the end I am unhappy with the outcome. Eventually I tear it all back down and do it right but I end up spending much more than I should have.

If I were in your situation I would have a reputable shop rebuild the current transmission. I would wait until I was completely prepared to conduct the 4L80E swap. I think it will be less expensive in the end, and less frustrating.

Best of luck to you either way.
 
58
4
8
Location
kingston/ NH
BLK HMMWV, thanks for the post.


I have a 24 volt alternator at 60 amps. As for the TCU, I am not set on either at the moment. I guess that the deciding factor is money and timeframe. The HMMWV is my daily driver, so I need it fixed quickly, but also need to save money.

As for the shifter, I just ordered the stock 4 speed HMMWV shifter.

Lastly, the driveshafts. That is one of the biggest questions. I believe the overall length will be 2.125” longer if I’m not mistaken.
If money is tight, sell the 4 speed shifter and modify the 3 speed for $20 to work with the 4 speed.
 

bcox11

New member
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Location
Oklahoma
Well, I’ve done to swap from 3l80 to 4l80e. But, I keep having issues with the TCU. I ordered the TCI kit as many of you have, but it isn’t working. It was showing that I was in 2nd gear at all times. Found out that the computer wasn’t sending 12v to the transmission. I got a replacement kit. I swapped out only the computer. Nothing else. Now I am getting 12v to the transmission, so it’s not showing that I’m in 2nd gear at all times. But, now it says I’m in Manual Shift Mode. This mode is activated when the Manual Shift Cable assembly has the blue wire grounded. I unhooked the computer entirely from the harness and check the harness blue wire for manual shifting. It’s not grounded, but it is in the computer. So, I got another replacement kit. Came in a day early. I swapped out on the computer. Now, the handheld says there is a comm error. The blue light on top immediately starts blinking when the computer is switched on. When I unplug the computer and plug the 2nd computer back in, no more comm error. But, I’m back to Manual Shift Mode issue. Manufacturer says it’s a bad computer. They said they can send me a new one next week “sometime”. Question I have now is, should I just send it back and buy a different kit from a different company? Or, try another computer from TCI. By the way, after each issue, I contacted tech support at TCI and they told me to swap out to a new computer.
 
58
4
8
Location
kingston/ NH
I used a US Shift Quick 4 and have not used any other controller, so my comments should be taken as such. In my reading prior to going with the Shift, I was leaning towards TCI, but a couple of posts (not just HMMWV, but CUCV guys) did have issues with the TCI. That pushed me to the slightly more expensive Quick 4. The BEC tech support guys were great, ID'ing and walking me through fixing an installation error (I didn't read the instruction warning on the page, oops!)

Seeing as you are going to the 3rd one, I would likely guess it is not the controller, but I would still go with another company. One of my friends who has a MV Shop recently used a Painless controller with good success.

.... Question I have now is, should I just send it back and buy a different kit from a different company? Or, try another computer from TCI. By the way, after each issue, I contacted tech support at TCI and they told me to swap out to a new computer.
 

osteo16

Active member
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Location
Evansville, IN
700R... would be my approach.. but that because i have a NP218.... change my input shaft and all bolts in.. Not as strong, but not doing rock work on the weekends.. Just a daily driver ... just my 2 cents.... Ill probably end up doing a 700R to NP218.. then change to a NP242 down the road.. Why.. because im bored..
 

Retiredwarhorses

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Brentwood, Calif
if I was researching this and had no idea what trans too install and found that the factory/military uses a 4L80e, as well as the vast majority of HMMWV shops performing conversions too same, I would do you self a favor and stick with the 4L80e.
 
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