Lmtv/fmtv air/crane attachment behind cab

[littlesfmtv]

I have seen a bunch of expedition builds that remove this very large and extremely heavy piece of steel from behind the cab, but no relevant information on wether or not it is considered a structural component.

I want to yank mine to extend my box and increase useful load, but have concerns it may be limiting frame twist to the engine/trans and could be inviting disaster long-term.

Does anyone here know if this is the case? I can't find anything in the tms related to it other than parts lists.

 

[Mullaney]

I have seen a bunch of expedition builds that remove this very large and extremely heavy piece of steel from behind the cab, but no relevant information on wether or not it is considered a structural component.

I want to yank mine to extend my box and increase useful load, but have concerns it may be limiting frame twist to the engine/trans and could be inviting disaster long-term.

Does anyone here know if this is the case? I can't find anything in the tms related to it other than parts lists.

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Maybe post a picture to know for sure what you are describing. There is a really heavy bar behind the cab that has about an 8x8 inch square tube that pulls out an insert on each side with a big eye. That is how the LMTV's are hoisted onto a boat. Is that what you are talking about? It can be removed...

 

[littlesfmtv]

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Maybe post a picture to know for sure what you are describing. There is a really heavy bar behind the cab that has about an 8x8 inch square tube that pulls out an insert on each side with a big eye. That is how the LMTV's are hoisted onto a boat. Is that what you are talking about? It can be removed...

That is the part in question. The two large extendable eyes and massive assembly that is, of course, huck bolted to the frame. If it can be removed without worry that is great news!

 

[ckouba]

I want to yank mine to extend my box and increase useful load, but have concerns it may be limiting frame twist to the engine/trans and could be inviting disaster long-term.

This is why I left mine in place. It looks quite structural. This may be due to applying the lifting forces when being slung but I figure it can't hurt to keep it.

Also, there might not be as much space to recover as you think. The expansion tank is about the same size in dia and needs to be located somewhere in that general area (above the cyl head level, not attached to the cab). I suppose you could replace it with a different shape tank though, which might free up what you need. I found it very useful to have a bit of that space for truck functionality though (induction system, expansion tank, cab lift pump, dipstick tubes, etc...).

This is what fills the space on my rig after I removed the spare tire crane and OE induction system:

 

[Awesomeness]

Lots of opportunity for theorycrafting on this one, but I don't think it was intended to be structural to the way the truck operates or drives. It is a lifting point for picking up the truck by helicopter/crane, and so it needs to be quite heavy and structurally sound to swing all that weight from it. However, even if it's rigidity was intended for its lifting uses, it's so beefy that it probably ends up adding stiffness to the frame. So it seems like a little bit of a "chicken or the egg" question.

If I were looking to remove it, I would start by examining a couple things...

1. Carefully look at it to see where it connects to the frame of the truck, and determine where it might be impacting strength and rigidity.
2. Look at other variants of this truck, the Styer truck it's based on, and other commercial trucks that are similar, and see if they have versions without it or if they have a similar brace even when they have no need for lifting the truck.
3. See if there is a way to modify the brace to make it smaller, without significantly impacting its structural support, such as cutting off the extended "wings".

That said, I've thought about making a rollbar connected to it.

 

[Ronmar]

I agree with Awsomeness in that it is structural to the point that it must distribute most of the truck weight thru a small portion of the frame without damaging it during a lift.

But it is connected to such a small portion of the frame its structural addition would be minimal if any. In fact, all the holes drilled in the frame to mount it probably removed more integrity than was added...

Because of its small length in relation to the overall frame length and it being perpendicular to the axis of twist, it would have little effect on overall twist. To reduce twist you would need large boxed/triangulated structures running lengthwise along the frame, not perpendicular to it. Like the 1088s have adjacent to their 5th wheel hitches...

Looking at the structure, i have no issue removing mine. You could always leave the side channels in place and cut off the part above the frame, or re-huck some sections of vertical channel where the lift arch was placed to try and recoup a little of tge integrity lost where the holes were drilled.

 

[chucky]

I would keep all 4 of them myself ! Its more great pulling points to tie to if you really sink her in something deep it lets more trucks tie to you at one time if needed and you slide the 2 out on the same side and hang you a hammock to each one for serious relaxing !

 

[Ronmar]

I would keep all 4 of them myself ! Its more great pulling points to tie to if you really sink her in something deep it lets more trucks tie to you at one time if needed and you slide the 2 out on the same side and hang you a hammock to each one for serious relaxing !

Yea they are good pull points, but you can add ones just as usefull that don’t get in the way of a habitat build. By pulling that stuff off of there I can fit a 17‘ habitat on a 4x4 and still keep the 40 degree exit angle…

@ckouba You don’t really need to keep the expansion tank above the head. Most exp/overflow tanks are below the head anyway. I had a genset that I used to maintain that had the overflow below the oil pan down on the lower frame

i think the only reason they put it where they did was to have a more convenient fill point, but there are ways around that.

 

[ckouba]

@ckouba You don’t really need to keep the expansion tank above the head. Most exp/overflow tanks are below the head anyway. I had a genset that I used to maintain that had the overflow below the oil pan down on the lower frame

There are two types of tanks- expansion (within the pressurized system) and overflow (open to ambient atmospheric pressure). I agree the overflow can go anywhere. I built a mid-engine car and my overflow tank is low and in the nose, and the expansion tank which feeds it is the highest thing in the engine bay other than bodywork.

The overflow tank's purpose is to catch any excess coolant which gets burped out when the system heats up and pressurizes. With a proper system cap at the expansion tank, excess air and/or coolant will get purged out into the overflow tank (not sealed to atm) and then sucked back in as the system cools down.

The expansion tank serves the purpose of bleeding air from the system and purging it out into the overflow tank if equipped with one. For it to function optimally, it should be the highest part of the cooling system, typically meaning higher than the cylinder head, so that the trapped air accumulates there and gets pushed out through the thermal cycling.

 

[Ronmar]

There are two types of tanks- expansion (within the pressurized system) and overflow (open to ambient atmospheric pressure). I agree the overflow can go anywhere. I built a mid-engine car and my overflow tank is low and in the nose, and the expansion tank which feeds it is the highest thing in the engine bay other than bodywork.

The overflow tank's purpose is to catch any excess coolant which gets burped out when the system heats up and pressurizes. With a proper system cap at the expansion tank, excess air and/or coolant will get purged out into the overflow tank (not sealed to atm) and then sucked back in as the system cools down.

The expansion tank serves the purpose of bleeding air from the system and purging it out into the overflow tank if equipped with one. For it to function optimally, it should be the highest part of the cooling system, typically meaning higher than the cylinder head, so that the trapped air accumulates there and gets pushed out through the thermal cycling.

It doesnt have to be located at the highest, point, it just has to be plumbed to the highest point.

The highest plumbed point on these systems is the small hose barb fitting on the upper tank of the radiator. It goes in and turns up right up against the top of the tank to get as much air out as it can. That port is plumbed to the bottom of the expansion tank… in ours using the expansion also as the fill point, with the large fill line and the coolant circ line running to the tank, the air that makes it to the rad will be displaced and find its way up to the exp tank. Most of the thermostat housing and upper rad pipe is higher than the radiator port, so you have to run the engine thru a heat cycle or two, to push that air to the rad where it can be sent to the exp tank And be purged.

but if you dont use the fill and circ line to the expansion tank and only connect the line from the radiator tank to the bottom of the expansion tank, you can put that tank anywhere just like an overflow tank. I put mine down in the front bumper. As the engine warms and the coolant expands, it expands into the expansion tank same as it always has. Any air in the rad will be pushed into the exp tank. Since the port is on the bottom, as the engine cools and pulls a vacume, only coolant will be pulled back into the radiator from that tank, just like it is now. Mine has worked fine like this for closing on 2 years now…

 

[serpico760]

This is why I left mine in place. It looks quite structural. This may be due to applying the lifting forces when being slung but I figure it can't hurt to keep it.

Also, there might not be as much space to recover as you think. The expansion tank is about the same size in dia and needs to be located somewhere in that general area (above the cyl head level, not attached to the cab). I suppose you could replace it with a different shape tank though, which might free up what you need. I found it very useful to have a bit of that space for truck functionality though (induction system, expansion tank, cab lift pump, dipstick tubes, etc...).

This is what fills the space on my rig after I removed the spare tire crane and OE induction system:

My thoughts exactly and I really like how you mounted those air cleaners I have purchased the same ones but haven't installed them yet.

 

[littlesfmtv]

Wow, I had no idea this would generate this much response. Ronmar, it was nice to meet you at the western round up and thank you for the info here. Part of my consideration is weight. I'm in a 1087, so she is already a big girl empty at 30k pounds. Every pound off the truck is +1 to my useful load. I'm extending the front of the box to give me a fixed location for the bathroom/shower. I even found a stainless prison shower stall with front plumbing access to use for the build. Unused, btw.

 

[littlesfmtv]

This is why I left mine in place. It looks quite structural. This may be due to applying the lifting forces when being slung but I figure it can't hurt to keep it.

Also, there might not be as much space to recover as you think. The expansion tank is about the same size in dia and needs to be located somewhere in that general area (above the cyl head level, not attached to the cab). I suppose you could replace it with a different shape tank though, which might free up what you need. I found it very useful to have a bit of that space for truck functionality though (induction system, expansion tank, cab lift pump, dipstick tubes, etc...).

This is what fills the space on my rig after I removed the spare tire crane and OE induction system:

What a cool build! Which Donaldson part numbers are those? I'd love to have just a tall narrow one to mount single sided.

 

[Ronmar]

Wow, I had no idea this would generate this much response. Ronmar, it was nice to meet you at the western round up and thank you for the info here. Part of my consideration is weight. I'm in a 1087, so she is already a big girl empty at 30k pounds. Every pound off the truck is +1 to my useful load. I'm extending the front of the box to give me a fixed location for the bathroom/shower. I even found a stainless prison shower stall with front plumbing access to use for the build. Unused, btw.

It was good to meet you as well. My concern is also weight, as well as height. i have no qualms removing my lift arch, although I am not really removing it as it is being repurposed into the habitat floor. As a rear “bumper”. That is where my taillights are going to reside.




As some reference material, the Steyr trucks do not have anything in that area. I used to have a good pic of one of their cab suspension systems that shows that area well, but cannot find it now. Probably deleted it as I am going to keep air. Here is a Steyr cab and chassis pic.

 

[Awesomeness]

As a rear “bumper”.

View attachment 905505

Serves extra duty as a battering ram.

 

[Ronmar]

Serves extra duty as a battering ram.

I walked into it the other day, might be handy for “re-locating“ a shoulder

 

[Mullaney]

I walked into it the other day, might be handy for “re-locating“ a shoulder

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How good were you?
No FLA's?

Almost as much fun as a Reese Hitch plugged into the back of a (insert vehicle name here) and you roll around the corner in a hurry. That THUNK sound on the chin will bring you to your knees... Almost takes your breath away!

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[ckouba]

What a cool build! Which Donaldson part numbers are those? I'd love to have just a tall narrow one to mount single sided.

Thanks. Looking around, I believe they are Donaldson PSD100033's. It'd be easy to stack two on a side, and in hindsight, that's what I might have done instead.

 

[chucky]

If you were going to put a habitat on your truck that is longer than the main frame like mine before you put the box on the frame you could use one of these airlift tubes with the extension to mount in the center frame at rear to have a long slide out pintle hitch so you could reach a trailer hitch ! Like a longer A 1R hitch !

 

[coachgeo]

the main chunk can be used for base of mounting a Roll Over Protection bar. Something to consider with these tin foil cabs.