FMTV chassis selection for camper build

[Mowen632]

Mods, I'm new here so please move this if there is a more suitable location for this thread.

I've come to the conclusion that I'd like to use an FMTV to build an expedition camper. I've read through quite a few of the threads here and on expedition portal that have helped me solidify my choice in this chassis but now I need a little more help from you experts.

I would like to build on a 6x6 chassis as I need a decently sized box to fit my family of 4. I am targeting a total length of 32-35' overall as I think it will be reasonably manageable to drive and with restrictions on RV access in national parks, this seems to be a sweet spot for both size and internal living area in the habitat. I expect this will allow for a ~24' to 30' box depending on the final length and if I relocate the spare tire and air intake.

So now I'm trying to determine which model truck I need. Due to the desired length, I am looking for a long wheel base FMTV. I used the info here:

https://fmtvtrucks.com/wp-content/uploads/sites/13/FMTV-A1-Variant-Configuration-Chart.pdf

After summarising this, It looks like there are 4 different wheelbases for the 6x6. 161" , 177", 209" and 217". The 217" is available on the M1086 and M1087. I have not found a single listing of the M1086 on GP. The M1087 expando vans usually go for a lot more than the cargo trucks and I think I'd be money ahead and get to fully customize the box if I build it myself, and they are still quite rare with a few popping up each year.

So that takes me to the 209" which is the M1089 wrecker. Seems like this is the best choice as they are pretty available on GP and the next step down would be the M1085 cargo which drops 32" off the wheelbase which would necessitate me adding that length behind the wheels to maintain the box size on a shorter chassis. My concern is all the extra stuff on the wrecker vs. a cargo which will have to be removed and sold or scrapped to get to a bare chassis. Might be making a bigger deal about this than it actually is, so I would welcome feedback.

I did a search for a TM for that chassis, but didn't find one. Can someone help point me to one? I think that may go a long way in educating me on what would need to be done.


TLDR:

1. Anyone have a manual for the M1089 Wrecker?

2. Anyone want all the stuff off the back of a wrecker if I buy one?

 

[ramdough]

Mods, I'm new here so please move this if there is a more suitable location for this thread.

I've come to the conclusion that I'd like to use an FMTV to build an expedition camper. I've read through quite a few of the threads here and on expedition portal that have helped me solidify my choice in this chassis but now I need a little more help from you experts.

I would like to build on a 6x6 chassis as I need a decently sized box to fit my family of 4. I am targeting a total length of 32-35' overall as I think it will be reasonably manageable to drive and with restrictions on RV access in national parks, this seems to be a sweet spot for both size and internal living area in the habitat. I expect this will allow for a ~24' to 30' box depending on the final length and if I relocate the spare tire and air intake.

So now I'm trying to determine which model truck I need. Due to the desired length, I am looking for a long wheel base FMTV. I used the info here:

https://fmtvtrucks.com/wp-content/uploads/sites/13/FMTV-A1-Variant-Configuration-Chart.pdf

After summarising this, It looks like there are 4 different wheelbases for the 6x6. 161" , 177", 209" and 217". The 217" is available on the M1086 and M1087. I have not found a single listing of the M1086 on GP. The M1087 expando vans usually go for a lot more than the cargo trucks and I think I'd be money ahead and get to fully customize the box if I build it myself, and they are still quite rare with a few popping up each year.

So that takes me to the 209" which is the M1089 wrecker. Seems like this is the best choice as they are pretty available on GP and the next step down would be the M1085 cargo which drops 32" off the wheelbase which would necessitate me adding that length behind the wheels to maintain the box size on a shorter chassis. My concern is all the extra stuff on the wrecker vs. a cargo which will have to be removed and sold or scrapped to get to a bare chassis. Might be making a bigger deal about this than it actually is, so I would welcome feedback.

I did a search for a TM for that chassis, but didn't find one. Can someone help point me to one? I think that may go a long way in educating me on what would need to be done.


TLDR:

1. Anyone have a manual for the M1089 Wrecker?

2. Anyone want all the stuff off the back of a wrecker if I buy one?

Do you intend to go off-road or just on dirt roads? The ultra long wheelbase and your box length will limit you severely to milder trails.

The 1089 manual is in the TM section with everything else.

Good luck. Post your build.


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[Third From Texas]

The 5-ton long chassis are not really all that uncommon. Tons of the M1085 with the cranes on the back are far more common (and a LOT less work to convert). Plus the value of a wrecker is far higher than that of a regular 5-ton long chassis.

And *if* you need to add length to a chassis, it would still be worlds easier than deleting a wrecker.

 

[ramdough]

I would not hang off the back of an M1085 unless you are not really going to go off-road. That rear overhang is a lot.

I would choose the 1085, then make you box match that length. Adjust your camper lifestyle to match.

If you only plan to drive on road, flat beaches, and dirt roads…. You can do whatever you want since you won’t care about your rear departure angle and break over angles.

It is your truck though and your money, so do what you want…. Just plan for the type of places you want to see.


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[mauinate]

I went standard 1088 and lengthened the frame about 3' behind the axles. Not really that bad in terms of drivability etc. My box is 8" from the cab and 20' long.

 

[B-Dog]

Ooof, I think it would sacrilege to destroy a wrecker....

But, I think what you're looking for (maybe?) is in the parts manuals. TM 9-2320-366-24P-1. Section 15 has details of the frames but no dimensions.
I'm guessing, if you carved up a wrecker, you would have no issue selling off the crane.

 

[GeneralDisorder]

You'll be money ahead to just find the M1087 and build from that. Ready made habitat. All other options will end up costing more. Just like the M1079 - price out an M1078 with a Globtrekker box vs the actual M1079. Yeah my truck (2008 M1079 A1R) wasn't cheap, but a good condition M1078 plus a habitat and sub-frame would cost roughly 20% more.

Rick

 

[Mowen632]

Thank you for all the input already!

Do you intend to go off-road or just on dirt roads? The ultra long wheelbase and your box length will limit you severely to milder trails...

I don't anticipate doing anything too crazy in regards to off-roading. We lived in a sprinter van for ~1yr and there were definitely campgrounds, forest service roads, and other places we would have liked to take it, but it was not capable. I expect to conquer some more adventurous roads, but I think the correct definition would be "road" and not "trail".

Do you consider the limiting factor to be the turning radius with the longer wheelbase or is it the break over angle? Our sprinter was a 170" WB so I have a frame of reference for that. I tried to use this link, to compare the turning radius of 177" vs 209" but I don't know if its accurate or the turning angle the truck is capable of. https://calculator.academy/turning-radius-calculator/#f1p1|f2p0

At 20° the difference is 40ft vs 47ft. At 30° that shrinks to 25.5 vs 30ft.

For breakover angle there is a calc here: https://www.vcalc.com/wiki/KurtHeckman/Breakover+angle
Looks like with 22" clearance at the middle of the truck going 177 to 209 drops the breakover from 28° to 24°

I would think even a big box on a M1083 or 1085 is pretty limiting just due to height and width. You're stuck to pretty wide open areas. Obviously, this isn't going where a jeep can go but neither is the M1083 with a shorter box.

The 5-ton long chassis are not really all that uncommon. Tons of the M1085 with the cranes on the back are far more common (and a LOT less work to convert). Plus the value of a wrecker is far higher than that of a regular 5-ton long chassis.

I would not hang off the back of an M1085...

Yes the 177" WB are pretty common on the M1084/5 and I absolutely agree that demoing all the stuff of a wrecker sounds like a lot of extra work which I would like to avoid. They also go for more than the cargo trucks for obvious reasons. We can fit a ~21' box on the M1085 without frame extension matching the length of the bed. and squeeze in another 2' if I relocate the tire. This might work and probably something to evaluate if I can make that box size work for us. 23' isn't too far off the 24' I had in mind as our minimum size.

I guess I feel like if I'm already going big (huge truck, huge habitat compared to a sprinter) then is it really a huge difference to go from a M1085 that is 29' long overall with a 23' box to a wrecker with a 3' frame extension that is 33' long and has a 27' box or something?

I feel like the extra 4' of box space (almost 20%) might be worth the potential for slightly less access. is that extra 4' going to keep me out of 20% more places that I would have gone if I were shorter? Probably not but maybe I'm underestimating this. the extra 4' could have a large impact on long term livability though.

It could be a good idea to get behind the wheel of a few long vehicles to test drive them. Sure I can get in some Class A/C RVs around this length to get a feel for differences even though this could be misleading since it will obviously be all pavement. Still likely a worthwhile exercise.

I went standard 1088 and lengthened the frame about 3' behind the axles. Not really that bad in terms of drivability etc. My box is 8" from the cab and 20' long.

Two if overland, used a M1083 (161") and added ~5ft to the frame to fit a 21' box with tire relocation. I don't see any reason to go with the 161 vs 177" WB though

Ooof, I think it would sacrilege to destroy a wrecker....

But, I think what you're looking for (maybe?) is in the parts manuals. TM 9-2320-366-24P-1. Section 15 has details of the frames but no dimensions.
I'm guessing, if you carved up a wrecker, you would have no issue selling off the crane.

I found M1078, and an FMTVA1 Electrical, I tried to search that TM in the forum search but was unable to turn it up (it just found this thread). I haven't had a chance to look through the M1078 manuals so perhaps I'll find what I am looking for in there. I'd welcome a link if you have it.

Glad to know someone might want some of the parts if we do go the demo route.

You'll be money ahead to just find the M1087 and build from that. Ready made habitat. All other options will end up costing more. Just like the M1079 - price out an M1078 with a Globtrekker box vs the actual M1079. Yeah my truck (2008 M1079 A1R) wasn't cheap, but a good condition M1078 plus a habitat and sub-frame would cost roughly 20% more.

Rick

Last 1087 on GP went for 75k. Not sure who got the one for 9k in may... https://www.govplanet.com/jsp/s/search.ips?k=m1087&sm=1&mf=1

I plan to self-build the habitat, so I don't think using Blissmobil or Globtrekker as a pricepoint is really an accurate comparison to what I expect to be able to do myself. Obviously, the huge savings is the amount of time I'll put into it (years) instead of buying it. Also using something that isn't purpose built will have its tradeoffs. I found some stats below on the size of the box. the truck is almost 33' long but the box is only 19.3' long. Also, I'm 6'4" so I could not stand up in the expanded sections.

Expanded L 232" (5,893 mm), W 160" (4,064 mm),
H (main section) 83" (2,108 mm),
H (expanded section) 75" (1,905 mm)


That said, it would be exponentially faster. I think if I had the opportunity to buy one at a reasonable price, I would probably jump all over it knowing I could get out there faster, and could build another box to swap out at some point down the road. However, odds of finding one at an attractive price seems low given their rarity.


Thanks for all the feedback! I look forward to some more!

 

[GeneralDisorder]

Self building, while possible, takes some engineering to do right. The issue is that unlike a normal RV, these vehicles are capable of some pretty extreme terrain and they have very flexible frames. More than one person has turned a self built habitat or an RV strapped to the back of an LMTV into kindling and toothpicks over rough terrain. The cost of the Globetrekker, etc boxes is because they are designed to handle the extreme loads of the chassis.

 

[Third From Texas]

Last 1087 on GP went for 75k. Not sure who got the one for 9k in may... https://www.govplanet.com/jsp/s/search.ips?k=m1087&sm=1&mf=1

The one that went for $9K was the one that hit the overpass while on a trailer. The habitat was totaled. And given the forces it saw, I'd worry a bit about the chassis. So it was a worst a parts truck, at best a long chassis.

 

[Mowen632]

Self building, while possible, takes some engineering to do right. The issue is that unlike a normal RV, these vehicles are capable of some pretty extreme terrain and they have very flexible frames. More than one person has turned a self built habitat or an RV strapped to the back of an LMTV into kindling and toothpicks over rough terrain. The cost of the Globetrekker, etc boxes is because they are designed to handle the extreme loads of the chassis.

Totally get it, I am a mechanical engineer and have done a good amount of reading on torsion free subframes. I think the FMTV is quite a bit less flexy than say an NPR or Unimog but everything has some level of flex. Considering I want a longer frame, total displacement would increase over a longer wheelbase, so some type of system needs to be implemented. Leaning towards rail on rail with captive springs. Seems like the easiest to build and incorporate into the box, as well as takes up minimal headroom compared to a 3 point and seems most that have used this (even on more flexible frames) have had good luck with it. I plan to do some testing once i have a truck in front of me so I can mock up some various mounting options and see how it would best be implemented. I'm sure I'll do a lot more research, CAD and FEA prior to actually building anything.

The one that went for $9K was the one that hit the overpass while on a trailer. The habitat was totaled. And given the forces it saw, I'd worry a bit about the chassis. So it was a worst a parts truck, at best a long chassis.

Makes sense it was so cheap. Probably could have answered that question for myself if I opened the listing...

 

[mauinate]

Totally get it, I am a mechanical engineer and have done a good amount of reading on torsion free subframes. I think the FMTV is quite a bit less flexy than say an NPR or Unimog but everything has some level of flex. Considering I want a longer frame, total displacement would increase over a longer wheelbase, so some type of system needs to be implemented. Leaning towards rail on rail with captive springs. Seems like the easiest to build and incorporate into the box, as well as takes up minimal headroom compared to a 3 point and seems most that have used this (even on more flexible frames) have had good luck with it. I plan to do some testing once i have a truck in front of me so I can mock up some various mounting options and see how it would best be implemented. I'm sure I'll do a lot more research, CAD and FEA prior to actually building anything.



Makes sense it was so cheap. Probably could have answered that question for myself if I opened the listing...

I'm doing rail on rail with captive springs. You can follow along on my youtube if you want: https://www.youtube.com/c/natevolk

 

[ramdough]

I'm doing rail on rail with captive springs. You can follow along on my youtube if you want: https://www.youtube.com/c/natevolk

Nate,

What are you putting between your rails?


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[mauinate]

Nate,

What are you putting between your rails?


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Just a rubber strip. Haven’t finished testing yet of different types but will mention it on the channel. Should be this month sometime I hope!

 

[Mowen632]

Just a rubber strip. Haven’t finished testing yet of different types but will mention it on the channel. Should be this month sometime I hope!

I'll take a look at your videos.

as for material between the rails, I was considering using "Cotton Duck Pad" or something similar. Some equipment I work on uses these anti-vibration pads at the mounting locations. There are lots of various types of rubbers and you can go pretty into the weeds with specific frequencies and whatnot which likely isn't necessary for this. The duck cloth caught my eye as it's pretty inexpensive, super tough and has thermal and vibration isolation characteristics. they use it at bearing locations for bridges. I planned to use it the full length of the rail. Might be something to take a look at or might be total overkill. https://grmcp.com/grm-cotton-duck-pads/

I'm sure I'll have some questions for you after I go through your build videos. Took a look at the first couple and great work on documenting it in such detail. Will be super helpful for those following in your footsteps!

 

[Gunny 0369]

I would not hang off the back of an M1085 unless you are not really going to go off-road. That rear overhang is a lot.

I would choose the 1085, then make you box match that length. Adjust your camper lifestyle to match.

If you only plan to drive on road, flat beaches, and dirt roads…. You can do whatever you want since you won’t care about your rear departure angle and break over angles.

It is your truck though and your money, so do what you want…. Just plan for the type of places you want to see.


Sent from my iPhone using Tapatalk

RAM, do you own a LWB FMTV?

 

[Gunny 0369]

Mods, I'm new here so please move this if there is a more suitable location for this thread.

I've come to the conclusion that I'd like to use an FMTV to build an expedition camper. I've read through quite a few of the threads here and on expedition portal that have helped me solidify my choice in this chassis but now I need a little more help from you experts.

I would like to build on a 6x6 chassis as I need a decently sized box to fit my family of 4. I am targeting a total length of 32-35' overall as I think it will be reasonably manageable to drive and with restrictions on RV access in national parks, this seems to be a sweet spot for both size and internal living area in the habitat. I expect this will allow for a ~24' to 30' box depending on the final length and if I relocate the spare tire and air intake.

So now I'm trying to determine which model truck I need. Due to the desired length, I am looking for a long wheel base FMTV. I used the info here:

https://fmtvtrucks.com/wp-content/uploads/sites/13/FMTV-A1-Variant-Configuration-Chart.pdf

After summarising this, It looks like there are 4 different wheelbases for the 6x6. 161" , 177", 209" and 217". The 217" is available on the M1086 and M1087. I have not found a single listing of the M1086 on GP. The M1087 expando vans usually go for a lot more than the cargo trucks and I think I'd be money ahead and get to fully customize the box if I build it myself, and they are still quite rare with a few popping up each year.

So that takes me to the 209" which is the M1089 wrecker. Seems like this is the best choice as they are pretty available on GP and the next step down would be the M1085 cargo which drops 32" off the wheelbase which would necessitate me adding that length behind the wheels to maintain the box size on a shorter chassis. My concern is all the extra stuff on the wrecker vs. a cargo which will have to be removed and sold or scrapped to get to a bare chassis. Might be making a bigger deal about this than it actually is, so I would welcome feedback.

I did a search for a TM for that chassis, but didn't find one. Can someone help point me to one? I think that may go a long way in educating me on what would need to be done.


TLDR:

1. Anyone have a manual for the M1089 Wrecker?

2. Anyone want all the stuff off the back of a wrecker if I buy one?

Welcome Aboard Mowen!

 

[ramdough]

RAM, do you own a LWB FMTV?

No, mine is a 1083. If I had the chance for a 1085…. I would have been happy with that as well. But, I would be hesitant to extend any further back than a 1085 already has as the rear angle is already pretty small and the overhang is a lot. That was my only point there. It comes down to personal preference really and what limits you want to accept.


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[Mowen632]

Welcome Aboard Mowen!

Thanks Gunny,

I took a look at your build thread for the exodus camper. Looks really really well done. Fantastic job. I've kicked around the idea of using a pre-built camper on the back as a shortcut to get going while I build a custom box on the side. Still toying with that idea a bit but I'm sure I'll have some more questions for you on your build.

it did give me some more confidence to look at building in some slides to the design which I had never considered before.

 

[Gunny 0369]

Thanks Gunny,

I took a look at your build thread for the exodus camper. Looks really really well done. Fantastic job. I've kicked around the idea of using a pre-built camper on the back as a shortcut to get going while I build a custom box on the side. Still toying with that idea a bit but I'm sure I'll have some more questions for you on your build.

it did give me some more confidence to look at building in some slides to the design which I had never considered before.

Lol
Mines not really a prebuilt camper anymore-

I think rebuilding my HAB took longer than it would take to slap those composites togather..
A full year.
What saved me time was reusing the interior components, after strengthening the hab framing..it gives my trucks a factory look.

my new trucks a bit bigger than the green, its been great in the woods - dont be afraid to take your big truck down those paths! And angle of approach? Ive got some pictures that will make you pucker.. lol