LMTV M1078A1 "Pandora" Build | 2024-??? | ***Picture Heavy***

[ARCowboy]

Hello all !

Last year I sold my diesel Chevy Colorado to fund a much bigger build, which I feel like I'm finally getting a start on. I've mostly been posting on SteelSoldiers and Coloradofans but have always wanted to get involved with the Expedition Portal community.

History
December of 2023, my wife and I ("we") purchased a 2002 M1078A1 we call "Pandora" (for a multitude of reasons haha). Like several others on here, we plan to turn this into an offroad camper. Some of the things that attracted me to the LMTV were:

• <26,000GVWR
• Non-DEF diesel engine
• Analog voltage control via relays/fuses
• Can be worked on by pretty much any [semi-]truck mechanic, diesel mechanic, or Caterpillar mechanic.
• More or less a blank canvas

Photo CAO 1APR2025




Perfectly camouflaged diesel powered patio

 

[ARCowboy]

Intent
I enjoy exploring the back country and primitive camping in different places (I think this is called "overlanding" but eh, who cares). When I retire from active duty, I want to take the trip of my dreams over 10,000mi from my home in North Carolina to the Red Woods of California, up to Denali in Alaska, and back home via back country trails and National Parks. If you have any suggestions for trails to take, places to camp, or things to see, I'd love to hear about them !




So I bought an LMTV… Pt. 1 - Aviator4x4

This is the day I got her home, after a 1200mi drive from TX to NC. Big shout out to my wife for letting me galivant off to Texas to buy an LMTV right before Christmas.


Priority

This was the planned build as of 23 Dec 2023


That list is now comically longer haha

 

[ARCowboy]

This was the first time I laid eyes on her. Fairly rust free, dry cab, really no dents in the body, and had the serpentine belt "upgrade".


Mmmm, pre-emissions Cat Diesel power.


I purchased some NOS Goodyear MV/Ts to put on it since the XMLs were from 2006. That is not the seller, just one of his mechanics.



And then went about replacing every single fluid in the truck as well as purchasing a cartload of basic tools from Harbor Freight (since I had flown to another state to look at/buy the truck).


Unfortunately the day after I wrote the check for it, the rear driveshaft went and took the trans with it. The plan was to have the driveshafts rebuilt before the drive home, I just thought I would have more than a day.


The seller took excellent care of me and I have nothing but respect for them. Honestly, they could sell this as an "experience" haha.


Lifting the bed off after cutting the huk bolts. Also not the seller, same mechanic that works for him.


Lifting the rear of the truck to roll it over the old trans. You can see how badly cracked the bellhousing was.



"New" transmission on this neat aluminum L track pallet he had sitting around. Wish he would have sold me the pallet ! haha. If anyone knows what this pallet is part of, or where I could find one, let me know !


After 8 days (that were somewhat stressful), she had a "new" transmission in and successful test drive. To summarize, in 8 days this was what I had learned, been forced to learn, and/or do:

• Drain and replace all fluids
  • Engine oil
  • Transmission oil
  • Rear Diff
  • Front Diff
  • Front hubs
  • Coolant
• What huk bolts are, and how to remove them with an angle grinder
• What transmission codes are and how to display them on Allison WTEC3
• How to remove/replace (R2) the entire transmission with a couple forklifts
• How to R2 the entire exhaust length
• That the driveshaft angle and RPMs on these trucks is extreme (EcoHubs awaiting install).
• That the truck's systems are pretty straightforward, unlike having a BCM that outputs PWM or CANBUS like my previous truck.
• That I still loved owning a military vehicle

After all that, I drove 1,200mi home from TX to NC... at 45-50mph listening to the sound of wind

 

[ARCowboy]

Reserved 3

 

[charlieaarons]

Think twice, then twice more before installing Ecohubs.
With 3.9 diffs, your top speed in your lowest gear (6.93) with 395 tires at 2400 rpm will be 12mph. Idle speed will be 3.5mph.
FMTVs do NOT have a low range transfer case, although I’m reliably told one can obtain a MVG-1150 (1.09-2.47 ratios, ~$27k brand new) from Marmon-Herrington, that’s a bolt-on.
Do you really want to be bouncing everything including the proverbial kitchen sink over rough terrain at 4mph? If you’re thinking “torque converter”, I still think you’ll be breaking stuff.
If the answer that creep speed is irrelevant, buy a Winnebago or whatever.
Consider the reasonable alternative of changing diff gearing to 3.07, leaving the planetaries at 2:1, and increasing highway speed with 14.00R20s. ~2000rpm at 60mph. Everyone’s experience is different, but IMHO (55 years in 4x4s, 17 years in a U500) 60mph is fast enough in vehicles like this with military tires.

 

[charlieaarons]

MVG-1150 | Marmon-Herrington

www.marmon-herrington.com

Alternatively 14.00s and 3.07 diffs speed you up 36% at a given rpm.

 

[ARCowboy]

Think twice, then twice more before installing Ecohubs.
With 3.9 diffs, your top speed in your lowest gear (6.93) with 395 tires at 2400 rpm will be 12mph. Idle speed will be 3.5mph.
FMTVs do NOT have a low range transfer case, although I’m reliably told one can obtain a MVG-1150 (1.09-2.47 ratios, ~$27k brand new) from Marmon-Herrington, that’s a bolt-on.
Do you really want to be bouncing everything including the proverbial kitchen sink over rough terrain at 4mph? If you’re thinking “torque converter”, I still think you’ll be breaking stuff.
If the answer that creep speed is irrelevant, buy a Winnebago or whatever.
Consider the reasonable alternative of changing diff gearing to 3.07, leaving the planetaries at 2:1, and increasing highway speed with 14.00R20s. ~2000rpm at 60mph. Everyone’s experience is different, but IMHO (55 years in 4x4s, 17 years in a U500) 60mph is fast enough in vehicles like this with military tires.

Certainly a lot to think about in there. I don't have any intention of driving over 70mph in the truck, and the goal of EcoHubs is to cruise at 60mph up/down minor to moderate hills with significantly reduced driveshaft RPM.

Most of my reasons why EcoHubs vs 3.07 come down to cost: at 200% the cost for a 14% performance difference, I can use the funds to enhance other parts of the build. I can also easily reverse EcoHubs in my driveway in ~2hrs; I've kept the original spider gears, labeled, and cellophane wrapped on a shelf if I want to move to 3.07 and 14R20 in the future.

That transfer case costs more than I paid for the entire truck, running, including the cost of fuel to drive it 1200mi home I'll accept one as a donation though.

With 1st gear @ 6.93 and 3.9 in the diffs w/ EcoHubs my final drive ratios will be somewhere in the middle of a 3rd gen Tacoma between 4H and 4L. With the truck launching in 2nd gear in "D" using 2-7, it is similar to the final drive ratios of a Tacoma using 1-6 in 4HI.



My lowest "crawl speed" will be as you say, around 4mph, but I'm not sure the torque converter locks up before 3rd gear. Also, I can use the brakes. I'm planning on expanding my wet tank to be a bank of 3 tanks which should allow me to ride the brakes for a little bit. And if I ride them too long/deplete air, the airbrakes will slow the truck down more as I lose pressure. The LMTV has a considerable CFM output from the engine driven compressor though, higher than most stock compressors.



Additionally, I have a set of custom valved Fox Commercial shocks awaiting install to further dampen/control impacts that load/unload the suspension.

 

[charlieaarons]

I do follow your reasoning, for sure.
However, do you actually have experience operating a ~25k lb truck, with a relatively low torque to weight ratio, in rough terrain loaded with innumerable fragile items?
And it’s always that “last 100 yards” in getting off a dirt road around the bend of a dry wash to a camping spot not visible from the track, for instance, that makes good offroad mobility important.
My mantra is that offroad mobility in heavy vehicles depends on 3 things: proper tires with ability to control pressure; locking diff(s); and proper gearing for the load and engine output.
In addition to of course ground clearance; IMHO suspension is somewhat mitigated by proper tire systems and locking diffs.
Not trying to rub it in, and I’ve never operated a FMTV with the Allison 3700SP, but I predict you’ll regret 3.9 final gearing if you venture even a short distance off “made” roads.

 

[ARCowboy]

I do follow your reasoning, for sure.
However, do you actually have experience operating a ~25k lb truck, with a relatively low torque to weight ratio, in rough terrain loaded with innumerable fragile items?
And it’s always that “last 100 yards” in getting off a dirt road around the bend of a dry wash to a camping spot not visible from the track, for instance, that makes good offroad mobility important.
My mantra is that offroad mobility in heavy vehicles depends on 3 things: proper tires with ability to control pressure; locking diff(s); and proper gearing for the load and engine output.
In addition to of course ground clearance; IMHO suspension is somewhat mitigated by proper tire systems and locking diffs.
Not trying to rub it in, and I’ve never operated a FMTV with the Allison 3700SP, but I predict you’ll regret 3.9 final gearing if you venture even a short distance off “made” roads.

Thank you for your concern, but the decision has been made.

It is my rig and I am going to build it how I want to. If I find that does not work for me, I will alter it and learn from the experience.

 

[Boucher]

M1078 Has the stock diff gears , with Eco hubs @1800 RPM Im running 60-65 in 6th gear. Climbing steep grades he does ok usually just a down shift to 5th but it has dropped to 4th and even 3rd on very steep grades. So far with stock gears I'm happy with the eco hubs.