lmtv top frame rail moved

[Gabe.ruesswick]

has anybody thought about or done a frame rail relocate. my application would be for a camper, if you could take the top frame rail and move it to the side of the bottom one it would save a fair bit of height and bring your cg down.

- am I dumb, is the top frame rail not just in the rear where the cargo bay normally is?
- is the idea dumb, would it drastically weaken the structure of the vehicle?
- other than thoughts on the idea?

If this has already been discussed please let me know and ill delete this thread.

 

[Gabe.ruesswick]

ill clarify that I don't currently own a truck so if some of my questions seem dumb that's probably why.

 

[Third From Texas]

You *could* but it would take a great deal of modding and fab. There are things bolted to the inside and outside of those frame members. You face a ton of rerouting of wires, air hoses, brackets, braces, etc. Both rails are just C-channel and I suppose you could flip two back-to-back.

I don't recall anyone ever doing what you suggest although I vaguely recall someone deleting the upper rail on a build that incorporated a articulating subframe for the habitat. *that may have been a Styre conversion, though (they only come with one frame rail).

If you look to the European cousins of the LMTV, you will find many have only one rail (but a LOT more twist).

 

[coachgeo]

Discussions in the past on this to that rail is part of the strength structure of the bed or 1079 box. It is NOT intended to be part of the trucks chassis. ... you can delete it and build your camper base to have it's own structural members as you see fit.

BUTTT..... there is a different matter to think about. the transmission sticks up well above the truck chassis and that rail.... so far that...... your back to using a tall sub chassis below your camper box to space up above it....... ORRRRRRR....you put a well insulated dog house cut into the floor of camper box (my intention)

Don't forget you will need some means to allow the truck chassis to flex independent of the camper box. I'll be using captured springs very similar to the M1079 setup

 

[Third From Texas]

Here's a Styer 12M18. Note it's being lower due to only having a single main frame. This one also has an articulating subframe for the hab:

 

[Guruman]

I was under the impression that not all of the variants have the top rails. I cannot remember which ones I thought did not have it, but I think I read something about this a while back and for the same reason, they were putting a box on it and needed to add a rail to get the height right for their application. Maybe it was a 5-ton though....

Am I wrong? (Hey, it happens.)

Edit: dang you guys are fast....

 

[Third From Texas]

Discussions in the past on this to that rail is part of the strength structure of the bed or 1079 box. It is NOT intended to be part of the trucks chassis. ... you can delete it and build your camper base to have it's own structural members as you see fit.

BUTTT..... there is a different matter to think about. the transmission sticks up well above the truck chassis.... so far that...... your back to using a tall sub chassis below your camper box to space up above it....... ORRRRRRR....you put a well insulated dog house cut into the floor of camper box (my intention)

Ah, the two maim frame rails are part of all S&S M-series trucks as far as I know . Are you thinking of the little 3rd frame member that it part of the M1079 hab?

IMO, deleting the secondary chassis will leave you twisting the frame like the 12M18 trucks do...

 

[Gabe.ruesswick]

Discussions in the past on this to that rail is part of the strength structure of the bed or 1079 box. It is NOT intended to be part of the trucks chassis. ... you can delete it and build your camper base to have it's own structural members as you see fit.

BUTTT..... there is a different matter to think about. the transmission sticks up well above the truck chassis and that rail.... so far that...... your back to using a tall sub chassis below your camper box to space up above it....... ORRRRRRR....you put a well insulated dog house cut into the floor of camper box (my intention)

Don't forget you will need some means to allow the truck chassis to flex independent of the camper box. I'll be using captured springs very similar to the M1079 setup

Im planning on doing a simple 3/4 point.

are you placing the mounts for your captured spiring directly on the Main chassis or are you using the existing second rail and captured spring mounts?

 

[Ronmar]

I was under the impression that not all of the variants have the top rails. I cannot remember which ones I thought did not have it, but I think I read something about this a while back and for the same reason, they were putting a box on it and needed to add a rail to get the height right for their application. Maybe it was a 5-ton though....

Am I wrong? (Hey, it happens.)

Edit: dang you guys are fast....

They all have it, it is modified for the specific application the truck is intended for, like in the picture of the M1079 picture shown. The M1080
(cab and chassis) has a plain secondary frame rail. I am going to turn my secondary rail/frame into my hab floor frame. Considering the weight I am calculating, the main frame will be fine to support a captured spring mounted habitat…

 

[B-Dog]

You can only lower the habitat a limited amount before the tires require wheel wells. Without the secondaries, the chassis will flex more and you'll need more clearance under the subframe. So, I'm not sure how much effort you want to put in for limited gains....
Assuming you're moving or deleting everything behind the cab, I think you're on the right track, ditch the secondaries (don't try to reuse them) and plate the outside of the frame rail. Obviously, it would be time consuming to remove everything off the frame, cut off ALL the huck bolts and match drill 100+ holes (the left and right hole patterns have slight differences). But, aside from handling the plates and heavy parts, it wouldn't be all that difficult. The only hose/wire that I can think of that would need to be dealt with is the supply to the dryer, just drill an oversized hole for the bulkhead nut/socket.

On the variants without the secondary C-channel, I'm really only thinking of the M1088 (not sure if there are others), they have reinforcing plates on the inside and outside of the frame rails.

 

[Gabe.ruesswick]

You can only lower the habitat a limited amount before the tires require wheel wells. Without the secondaries, the chassis will flex more and you'll need more clearance under the subframe. So, I'm not sure how much effort you want to put in for limited gains....
Assuming you're moving or deleting everything behind the cab, I think you're on the right track, ditch the secondaries (don't try to reuse them) and plate the outside of the frame rail. Obviously, it would be time consuming to remove everything off the frame, cut off ALL the huck bolts and match drill 100+ holes (the left and right hole patterns have slight differences). But, aside from handling the plates and heavy parts, it wouldn't be all that difficult. The only hose/wire that I can think of that would need to be dealt with is the supply to the dryer, just drill an oversized hole for the bulkhead nut/socket.

On the variants without the secondary C-channel, I'm really only thinking of the M1088 (not sure if there are others), they have reinforcing plates on the inside and outside of the frame rails.

I've got a Milwaukee portable mag drill so I'm not worried about copying the holes over, as for wheel wells I've already got them accommodated in my cad drawing. id definitely be removing the spare tire carrier and redoing the intake/ filter to stuff my box up to the cab. as for a little bit more frame flex I don't hate the idea, help keep the rears on the ground in extreme situations.
- what thickness plate would you guys use to reduce frame flex?
- what's everybody's thoughts on adding more cross braces between the two frames to reduce flex?
-can anybody tell me the distance between the frame rails? id like to put my batteries between them with a access panel through the floor.

 

[B-Dog]

I've got a Milwaukee portable mag drill so I'm not worried about copying the holes over, as for wheel wells I've already got them accommodated in my cad drawing. id definitely be removing the spare tire carrier and redoing the intake/ filter to stuff my box up to the cab. as for a little bit more frame flex I don't hate the idea, help keep the rears on the ground in extreme situations.
- what thickness plate would you guys use to reduce frame flex?
- what's everybody's thoughts on adding more cross braces between the two frames to reduce flex?
-can anybody tell me the distance between the frame rails? id like to put my batteries between them with a access panel through the floor.

haha no mag drill would be a hard stop on that entire idea.
29 3/4" between the rails.

A suggestion on thickness would be a shot in the dark without a lot of engineering. A 3/4" x 7" plate has a similar area moment of inertia (resistance to bending based on the shape) as the secondary frame rail; only looking at bending when viewed from the side of the truck. Since the frame rails are stacked, the problem is probably a lot more in depth.

Same with cross braces....lots of engineering to give you any kind of factual answer.

 

[Gabe.ruesswick]

haha no mag drill would be a hard stop on that entire idea.
29 3/4" between the rails.

A suggestion on thickness would be a shot in the dark without a lot of engineering. A 3/4" x 7" plate has a similar area moment of inertia (resistance to bending based on the shape) as the secondary frame rail; only looking at bending when viewed from the side of the truck. Since the frame rails are stacked, the problem is probably a lot more in depth.

Same with cross braces....lots of engineering to give you any kind of factual answer.


Im not too worried about frame flex from the side-view, my camper wouldn't be anywhere near the weight needed to seriously bow the frame rails, id be more concerned with frame twist than anything. I agree lots of engineering to do it right, I've got friends that are studying to be mechanical engineers to help, just depends how many beers they charge by the hour...

"haha no mag drill would be a hard stop on that entire idea." are you saying you don't think a mag drill wouldn't be up to the task... or that mag drill would make light work of it?

thanks for the measurement between frame rails, the batteries I've got my eyes on are only 22 wide so that should work out just fine with space around them for insulation.

I don't know why this is all in a quote I can't seem to pull my text out

 

[coachgeo]

Im planning on doing a simple 3/4 point.

are you placing the mounts for your captured spiring directly on the Main chassis or are you using the existing second rail and captured spring mounts?

captured spring directly on the Main chassis. Ambo box am using was (sorta) manufactured to sit maybe 1" above Freight liner chassis it came off of . There are six beefy L brackets w/rubber isolator pads. These bolt to the truck chassis; outboard of the chassis. The ambulance box mounts thru the isolators to them. Plan is to modify the brackets w/isolators to be similar in concept to the M1079 set up. (captured spring sitting in a cup. Thinking front to be sprung using same spring tension as M1079. Middle being less sprung (does not exist on 1079)..... rear most would be solid mount same as is done with the M1079 and the Ambulance.

The ambo box has wheel wells already. May have to enlarge?
below is freightliner chassis it came from. Chassis measured the same width as LMTV

i

 

[coachgeo]

Here's a Styer 12M18. Note it's being lower due to only having a single main frame. This one also has an articulating subframe for the hab:

View attachment 865762

apples oranges because how the transmission fits into the truck chassis. This makes the FMTV completely different thus no comparison when it comes to design ideas. You'll notice in this setup a fellow used to remove his trans....it is taller than the subframe of typical subframe of bed or boxes used on these trucks.

 

[Third From Texas]

apples oranges because how the transmission fits into the truck chassis. This makes the FMTV completely different thus no comparison when it comes to design ideas. You'll notice in this setup a fellow used to remove his trans....it is taller than the subframe of typical subframe of bed or boxes used on these trucks.

View attachment 865884

More like Styre to Steward & Stevenson.

You know that *I* know about the trans protruding (keep in mind I was going the ambo route same as you before I found the M1079). And you and I both know that many builds have accounted for the trans protrusion. If you look at the other image that I posted showing the frame sections, you'll notice that little subframe attached to the M1079 box. I bet you can guess one of the purposes it serves. (hint: it keeps the hab from hitting something below that's right in the area we're now discussing).

But the Styre image is still applicable for the reason I posted it. Accommodating the trans "hump" on the S&S trucks is as simple as incorporating a "hump" in the hab floor or elevating above it. I've got pics somewhere of a number of various makes truck conversions being built that have to notch out the hab to clear the trans. So it's not really unique to S&S trucks. If you look very closely at the Styre image up thread, you'll even note that it's trans protrudes above the frame rail (albeit only slightly).

 

[Third From Texas]

You bring up a good point with the trans, though. The OP is looking to lower his frame/COG/hab. He will have to incorporate a "hump" into the design to allow for the trans (and it's gonna be a BIG hump protruding into the hab). Else he'll have to raise it to the height of the M1079 hab (which is *really* high).

 

[Ronmar]

Yep, hump for the trans, water tanks and some of the other hab systems inside the bed platform will go over top of it…

 

[coachgeo]

More like Styre to Steward & Stevenson.

You know that *I* know about the trans protruding (keep in mind I was going the ambo route same as you before I found the M1079)....

LOL....... have got the memory that puts names with rigs and projects like a steel trap. Just so happens that steel trap is 100ft under the saltiest of oceans and there is no metal left.

least now I have tiny excuse and just blame it on age.... in reality it's always been that way lol. Extremely conceptual understandor... (eventually)... names of things, people, time things happened... forget it

btw would love to see some of your shots of camper boxes with trans tunnel/dog house. Actually not seen that before.

 

[Third From Texas]

LOL....... have got the memory that puts names with rigs and projects like a steel trap. Just so happens that steel trap is 100ft under the saltiest of oceans and there is no metal left.

least now I have tiny excuse and just blame it on age.... in reality it's always been that way lol. Extremely conceptual understandor... (eventually)... names of things, people, time things happened... forget it

btw would love to see some of your shots of camper boxes with trans tunnel/dog house. Actually not seen that before.

Here's one that I had saved that just jumped out at me. It's from a Fuso build over on Expo Portal in the "other overlander trucks" forum. If I recall, the Fuso even has a forward section of frame that curves up along the trans.

Not exactly what I was thinking of. I have pics of habs being framed up and a good number had a "hump" notched out center-board (not all the way across to both sides like this Fuso).

I have a bunch more stuffed in folders here somewhere. I kinda stopped looking at box designs once I got the M1079..