Transmission Swap

Hello members, new guy here! Wanting to know if the 6.2 engine / transmission that is a 3 speed can be swapped out with a 4 speed and what all does it involve please. Thanks in advance.

I am in the market for a vehicle and was trying to educate myself a little before jumping into something that I may regret.

If you want a 4spd, buy one. Its way less hassle and you don't have a (major) project to do before you get to drive it.

I'm with gimpy. If you already own one, it's a lot of money and headache to get the TH400/3L80 switched over to the 4L80E. If you don't yet own one, it's worth the $3-5k premium to just buy a truck that has a 4L80E already in it. I'm doing the swap-over and have made several very expensive mistakes even after tons of research. Without making any mistakes, several of the parts I bought were defective, drastically increasing the cost. As well, I've spend dozens if not hundreds of hours researching and actually working on the truck for the build and install. Buying a 3 speed with the intent to switch it to 4 isn't worth it.

Well to answer your question yes it can be done.
Like all the other guys say it's better if you can find one with a 6.5 N/A or 6.5 Turbo and the 4l80 in it already.
To me no point in just trying to add 4l80 to 6.2
When I first did the upgrade from 6.2 w/ 3l80 to 6.5 N/A w/4l80 I tried the aftermarket trans controller made by EZ TCU because I didn't want to change out my main body wire harness.
controller was around $460 ??
New main body wire harness for 6.5 N/A $2,400 ? if you can find one now.

After spending the money on the EZ TCU
I ended up switching it out to the military controller and changing out the harness.

Short list of things your going to need to also change no matter what controller you use (military or one of the after market)

Front and rear drive shafts will need to be shortened
Possibly front and rear diff's . ( up to you)
front and rear cross members ?
Shifter and linkage,
Dual voltage 200 amp Alternator ( especially if trying to go with military Trans controller)
sheet metal panel with breaker and relays ( mounts behind front passenger seat / back of battery box in rear passenger foot well) new style transfer case ( not sure if you can still use the old one ? but why ?
Fuel tank
I'm sure I missed a lot of things.
Plus your going to need some sweat equity and a place to work on it .
RWH has a way to swap out the main body wiring harness without removing the body from the frame. ( Obviously his skill set far surpasses mine. I had to separate the body and frame. Now you need even more space and a few friends with bitchin tools like lifts and hoists.

If I hadn't already owned the 6.2 3l80 money pit for 14 plus years I would have found a newer money pit with the 6.5 4l80 already in it.

GW

Get one already done, then just fix the broken/worn part if there is any.
If truck has the GEP 6.5na, thats also a plus.

What exactly is this?

86humv said:

Get one already done, then just fix the broken/worn part if there is any.
If truck has the GEP 6.5na, thats also a plus.

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Let me ask this. Is the 6.2 , 3 speed that much of a headache? I am looking to drive to an from work, 8 miles and to have something 4wd for hunting and camping that isn't the same as all the other options.

biggdadd58 said:

Let me ask this. Is the 6.2 , 3 speed that much of a headache? I am looking to drive to an from work, 8 miles and to have something 4wd for hunting and camping that isn't the same as all the other options.

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Its slow for sure. We drive one of ours 140 miles back and forth to new orleans often. It's not necessarily a headache, just slow which can cause a headache sometimes for long trips ... for what you describe you'll be fine for that short distance.

Sent from my SM-N950U using Tapatalk

Are you mechanically inclined?
I'm not trying to be a smart ass I'm just asking.
If you like wrenching on things and doing your own PM work then you found something that isn't the same as all the other options.
If not I'd stick with the other options.

Food for thought:
It's going to be slower then all the regular options. If you travel for any length on the highway before you go off road especially with a group.
Wider then the other options if you hunt in the woods with narrow roads and trails.
More complex to find spare parts for out in the middle of nowhere.
Harder to find a shop to fix anything almost anywhere.
Harder to find a tow or flat bed to come get you in the middle of nowhere.
Hard to jump start out in the middle of nowhere if your the only military truck in the group.

No offense taken, just a great question to ask. I don't mind wrenching and all your other comments were good ones as well. I am looking for something "different" at this late stage in life. I missed the mid life crisis thing due to working too much. Still doing the working thing but thought of trying one of these for a long time. Long trips are not in the future for this ride, nothing over an hour or two. I would like to find someone out there that has a good one for sale, something that has been gone over and not needing a lot of work to enjoy. Owning my own business has backfired and it seems to be owning me at the moment, so wrenching to get it on the road is something that I can't fit into the schedule at the moment.

BLK HMMWV said:

Are you mechanically inclined?
I'm not trying to be a smart ass I'm just asking.
If you like wrenching on things and doing your own PM work then you found something that isn't the same as all the other options.
If not I'd stick with the other options.

Food for thought:
It's going to be slower then all the regular options. If you travel for any length on the highway before you go off road especially with a group.
Wider then the other options if you hunt in the woods with narrow roads and trails.
More complex to find spare parts for out in the middle of nowhere.
Harder to find a shop to fix anything almost anywhere.
Harder to find a tow or flat bed to come get you in the middle of nowhere.
Hard to jump start out in the middle of nowhere if your the only military truck in the group.

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I stuck with the 3 speed for one reason. Cost. I couldn't justify that amount of money just to go faster. When I get on the highway I stay about 50MPH. Yes I can go a little faster but why? If I need to go faster I will drive my 2500HD. It sounds like you would be just fine with a 3 speed. If you are only going 8 miles each way. If you really want to go faster maybe look into the 700R4 swap. As long as you are not towing crazy loads it might be a better option for you. Do a search you will find a lot of info on it here.

biggdadd58 said:

Let me ask this. Is the 6.2 , 3 speed that much of a headache? I am looking to drive to an from work, 8 miles and to have something 4wd for hunting and camping that isn't the same as all the other options.

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I drove one (3spd/6.2) from KS to GA and back recently.

So no, it just isn't that big of a deal. Much higher priorities for the $ it'd take for the difference. Sure, I'd like another gear or two, but it just isn't that big of a deal.

700R4 is def. the way to go when looking for more MPG and higher cruising speeds.
Throw in a 2wd/4wd transfer case and now your really talking !

JoeJrTheBarber said:

700R4 is def. the way to go when looking for more MPG and higher cruising speeds.
Throw in a 2wd/4wd transfer case and now your really talking !

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Why would you want a 2wd case?

98G said:

I drove one (3spd/6.2) from KS to GA and back recently.

So no, it just isn't that big of a deal. Much higher priorities for the $ it'd take for the difference. Sure, I'd like another gear or two, but it just isn't that big of a deal.

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you can always buy bigger tires for an extra “gear”

Skrilex said:

Why would you want a 2wd case?

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Better MPG, Faster tollway speeds, less wear and tear on driveline parts.

I can’t think of how these would be true unless you could install manual hubs somehow.

Skrilex said:

you can always buy bigger tires for an extra “gear”

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At the cost of taking away from the bottom end acceleration in direct proportion to what you're adding to top speed. And of course the cost of replacing tires.

Not enough return on investment in my opinion. The 37's are fine. Cruising speed 55ish is fine.

I'm not anti-mod or anti- tires and a lift. Everything is a set of compromises. The stock configuration on the M998 is an adequate set of compromises for me.

There's all kinds of stuff we could do to make them a better interstate road trip vehicle. Thing is, if I wanted an interstate road trip vehicle I wouldn't use this platform as the basis.

Back on the topic of the 4spd vs the 3spd - the 4spd is better all around. But it's also considerably more expensive to get one with it already in place (for good reason), and installing one in place of the 3spd isn't a trivial undertaking.

For the guy who uses it off road, around town, and an occasional trip a couple of hours away the 3spd should be fine.

JoeJrTheBarber said:

Better MPG, Faster tollway speeds, less wear and tear on driveline parts.

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Skrlex is correct. The front axle turns all the time any way. There is no lockout hub or center axle disconnect. a 2WD tcase won't change anything.

ken said:

Skrlex is correct. The front axle turns all the time any way. There is no lockout hub or center axle disconnect. a 2WD tcase won't change anything.

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It would change the way the HMMWV handles. For the worse. IMO. There has been a lot of discussion about this on H1 forums.