LMTV Frame twist

[coachgeo]

I agree that the expo portal thread is way to convoluted now.... Wish a wise moderator would split it up into new threads.... each one being made up of the different threads on one particular way of doing a pivoting mount. I started one over there specifically aimed at the captured spring mount system. Might even be that thread where the sliding plate for lateral control was discussed. Think may have mentioned it here as well.

 

[utahpow]

Contact Quade who made his own sub-frame and worked with a German engineer to get it right on his M1088: https://www.instagram.com/overlandadventuretruck/. There is a lot of guessing going on right now, and these guys IMO have got it right. But that depends if you are thinking of your truck and box as an investment and potential re-sale value. If not - just attach it to the bed. Otherwise, take note from those doing it right.

 

[1951M1078]

Think that truck is for sale also.

 

[utahpow]

Quade built the truck up to sell later to fund his expedition truck business. It's a calculated move in my opinion, after speaking with him on his intentions.

 

[Reworked LMTV]

Well that's interesting, the bed is heavy I think close to 5000 pounds. Because I could not lift it with a 2000 lb chain fall. I don't think the camper will weigh half that. I also would like to soften the ride of the camper which air bags should do.

What kind of camper construction are you using? Composite?

 

[scottmandu]

Well that's interesting, the bed is heavy I think close to 5000 pounds. Because I could not lift it with a 2000 lb chain fall. I don't think the camper will weigh half that. I also would like to soften the ride of the camper which air bags should do.

weight is in the 3500 lb range for a bed.

 

[1951M1078]

Don't have the numbers here but my M1078 bed was way under 3000#. Think it was 2400#. My fork lift picked it up no problem at idle.

 

[Shakkles]

I'm necro'ing this thread because, since lots of people are now buying these trucks to build a camper on the back and they will no doubt eventually find this thread as i did, a critical point still remains missing from it. Someone even went so far as to say that with the bed removed "there will be more flex".

The fact that nobody seems to have gotten right though is "flexing will occur at the point of least resistance". The reason people are building all these torsion-reducing spring packs, adding 10 inches to the height of their already insanely tall habitat build is because they're either forgetting this fact or simply didn't think about it.

Here's an example. You're the guy lifting one wheel up with a fork lift, pointing to the flex in the frame and saying, "look, the frame twists". The fact is the frame is twisting because, again "in this scenario, IT is the point of less resistance". And why would that be? Because the suspension in the rear is configured for an IMMENSE load that isn't in existence at that moment, thus, it stays mostly rigid. Plus you're leading the rear anti-sway bar intact... Dude... That's literally what it's there for; To physically prevent the wheel you just lifted from lifting any more than it's opposing wheel.

My truck build goes a different route and includes the removal of one leaf on both sides of the rear and a rear sway-bar disconnect, and ive even considered simply replacing the springs altogether with airbags, because in this setup, when you "lift a wheel with a forklift", the suspension actually does what it should and flexes, meaning, the frame doesn't to any significant degree eliminating the need for and overengineered torsion-free setup.

I feel like this is the exact same "evolved solution" as what happened with the "swap out the pinion gears to get highway speed", which was better than nothing, but an incredibly inefficient and incorrect way of "fixing the low speed problem" by ramping up the speed of the already far-too-fast running gear (the main cause of driveshafts splintering) just to overcome the fact it's going to be chopped by 50% once it hits the wheels.

Eco hubs was the smart and correct fix.

Fix the disease, not the symptoms. In this case; Correct the problem that the suspension isn't doing it's job and your frame won't have to be the weak-link and thus you won't have to add a whole new torsion-free chassis over it.

 

[Ronmar]

"flexing will occur at the point of least resistance". Yes and no... What also determines this is where and how the force is applied. This can be an issue with the 3 and 4 point engineered subframes, as they concentrate all the force from the habitat mass into those 3 or 4 points. if not engineered properly those points now become the high stress point and can result in fatigue/failure...

What you say about suspension is correct, if it does not yield, it imparts force to the frame, and softening plus disconnecting can increase its travel. The way you describe sounds like a viable one except it may be missing part of the overall picture, that being overall balance.

"This thing is nose heavier than the Ayotolla" Quick, what movie is that from?

You are going to remove weight from the rear and reduce the suspension spring capacity in the rear to match the weight? How are you planning on removing weight from the front to maintain axle balance? In my experience, nose heavy, or tail heavy vehicles don't perform as well as balanced ones in just about every situation... Are you planning on running the stock single channel CTIS, because your tires may have something to say about a nose heavy config running the same tire pressures front and rear as provided by CTIS...

From what I have gleaned from peoples reports of loaded axle weights, you need to add at least 3K to the bed of a 1078 to approach axle balance. If you remove the bed, its going to take close to 6k to balance axle weight. and when you get back to those weights, the stock rear springs are closer to being back in play... But sway disconnects would still be nice in really rough terrain IMO.

I got a M1079 bare cab and chassis from auction(basically a M1080). Because I wish to maintain axle balance, this is one of the few builds where my only concern IRT weight is that I may not be adding enough. To keep height under control I am making that top 6" frame rail into the habitat floor frame. it will be attached at one end, and captured hydraulic "springs" at the other end to allow the main frame to twist as needed. This saves me at least 6" overall height and gives me a very strong habitat floor to support the all steel rib and skin habitat box...

My finished interior height should be ~6-11", with an overall finished exterior height, including solar and guards, right at 12'. that with a 6" tapering to 3" floor thickness, 3" wall thickness and 3" arching to 4" roof thickness. I think the OE springs will be OK at the ~20K all up weight. havn't figured out how to work disconnects for that large a swaybar yet

A few ways to fry this fish...

My .02

 

[Shakkles]

Hey Ron! I just finished watching your video about resetting idle with the on/off and accelerator-press method actually.

So I've thought about the axle load front/back a lot. First and foremost because, as almost impossibly unlikely it is to occur, i am TERRIFIED of hitting the brakes too hard and the front end hitting the pavement lol. If you think about it... We're really trusting a lot in that "one single lock that doesn't even make a locking sound when you lower the cab back down after servicing the engine compartment.

The engine and cab together are massively heavy however the bed itself is (if I get BrokeOverland scale experiment conclusions correct) still even heavier, and with the transmission nearly in the center of the truck, my conclusion is that the reduction of one leaf in the rear is utterly negligible when you factor in the massive payload the truck was designed to carry back there. In fact i'm 100% convinced that, for the troop-carrier versions, some engineer was making a strong strong case to have less springs, but the reason we have all 4 was just cut costs while provide uniformity across platforms. Even with one leaf removed on each side side and no swaybar it's incredibly difficult to get those wheels to flex at times. HOWEVER... I don't have a 100% full habitat yet so as i'm unable to test the real-world results of highway-travel with a fully-loaded habitat it's possible i might change my mind at that time.

Basically my build is designed to be different from everyone else's in one simple way that seems utterly unimportant to every single other build i'd seen but absolutely 100% critical to myself; Height. As low of a roof and center of gravity as physically possible. My dream is to actually live in this thing in the woods, and also where i live there are DOZENS of bridges that are under 11' and you don't know it until you're 150 feet from them going 60mph. And if it's isn't low-bridges it's low street lights, low overhangs and branches everywhere. No, nope. There are just too many caveats to tall boxes and too many benefits to shorter/lower ones.

The "difficult, tricky, but maybe not impossible" mission statement is:

1) No more than 10'2" tall at the tallest point
2) Able to stand-up inside the habitat, even if it is only "sections" of the habitat such as recessed between the frame rails.
3) I'm 6' tall.

The whole "you don't need a zero-torsion solution" just came as an completely accidental epiphany when designing a solution to meet those goals.

 

[Ronmar]

Not utterly unimportant to everyone. height was pretty high up on my list also, which was why I converted the upper frame into the floor(mine is different than everyone else's too). If you take off your bed, stand on the frame, that is ~3/4" lower than where my finished floor will be. my top height(top of solar) will be ~7'6" above that frame top. To compare a bit average height of a class A is 13'6" travel trailers and 5th wheels average ~11 and 12' respectively.

With the base frame height so high, you are going to be hard pressed to meet 11'6" OA without having to live like a hunchback in a cave(first way i drew it) and the only way I see anything close to 10' is with a pop top and that is a whole nother can of worms structurally and environmentally that I did not want to try.

You don't need a zero torsion subframe, but you do need a habitat that can withstand the amount of flex you do encounter. soft suspension or no, you will still see frame flex...

 

[GeneralDisorder]

Frame flex is unavoidable and needs to be accounted for. You can't just soften the suspension and cross your fingers..... Pocketed springs are the lowest profile option, they are simple with no complex moving parts and are what the original designers used for the M1079 and M1087 - but they do require a box that is built literally like a tank. THICK riveted aluminum, corner and edge reinforcing, and very ridgid panels..... And if you go very low with the box then you have to build in a transmission hump.

The trucks are generally over-sprung for their new life as a civilian truck that is true (look at the A1R front coil springs for example) but you aren't going to eliminate frame flex no matter what you do so you have to address it or it will turn your fiberglass/plastic/tree carcass habitat into bark dust and splinters.

 

[Shakkles]

Not utterly unimportant to everyone. height was pretty high up on my list also, which was why I converted the upper frame into the floor(mine is different than everyone else's too). If you take off your bed, stand on the frame, that is ~3/4' lower than where my finished floor will be. my top height(top of solar) will be ~7'6" above that frame top. To compare a bit average height of a class A is 13'6" travel trailers and 5th wheels average ~11 and 12' respectively.

With the base frame height so high, you are going to be hard pressed to meet 11'6" OA without having to live like a hunchback in a cave(first way i drew it) and the only way I see anything close to 10' is with a pop top and that is a whole nother can of worms structurally and environmentally that I did not want to try.

You don't need a zero torsion subframe, but you do need a habitat that can withstand the amount of flex you do encounter. soft suspension or no, you will still see frame flex...

Dope! Makes my day to hear someone I follow for advice has a similar thinking. Yup... The problem is we have these 47" tires and etc. And i say "problem" because "I cannot physically bring myself to put smaller tires on something that had 47"ers lol. You just "can't go smaller" once you have had bigger as a dude, it's just not doable, at least for me.
For about 6 months before deciding on the M1078 I was going to go with a Mitsubishi Fuso 4x4 instead and they do have smaller tires and lower height, but 99.999% of the Fuso 4x4s you see for sale are all right-hand drive imports with 380,000 miles. Plus their frame and overall build is nowhere near as robust and capable for "building a house on the ass end of it".

And agreed about the "pop-top", because if money were no object, i absolutely would simply build one with a raising roof and walls on linear rails. I've seen i think 2 of them online that both sold so i know it's possible, just adds a whole another dimension (literally) to the build.

 

[olly hondro]

Going smaller tires...yeah I get that I just transitioned to 49s from 53s, kinda hurt my pride but makes more sense with the gear change.

 

[Shakkles]

Going smaller tires...yeah I get that I just transitioned to 49s from 53s, kinda hurt my pride but makes more sense with the gear change.

Then you're a tougher man than I my friend

I've also been having some crazy thoughts about the possible ramifications of slinging the axles above the leafs instead of below... Keep the same sized tires but the frame, the cab, and the whle truck just dropped what... 7 inches or something? Every single time i'm getting off the highway on an off-ramp i always wish the truck were 7 inches less tall lol

Also, i got a response from the maker of "Optimus", an lmtv with a habitat bolted right onto the frame who states no issues in 5 years. I dunno that is 100% accurate, but i do know that's definitely what he's claiming.

 

[Shakkles]

Then you're a tougher man than I my friend

I've also been having some crazy thoughts about the possible ramifications of slinging the axles above the leafs instead of below... Keep the same sized tires but the frame, the cab, and the whle truck just dropped what... 7 inches or something? Every single time i'm getting off the highway on an off-ramp i always wish the truck were 7 inches less tall lol

Also, i got a response from the maker of "Optimus", an lmtv with a habitat bolted right onto the frame who states no issues in 5 years. I dunno that is 100% accurate, but i do know that's definitely what he's claiming.

 

[aw113sgte]

Then you're a tougher man than I my friend

I've also been having some crazy thoughts about the possible ramifications of slinging the axles above the leafs instead of below... Keep the same sized tires but the frame, the cab, and the whle truck just dropped what... 7 inches or something? Every single time i'm getting off the highway on an off-ramp i always wish the truck were 7 inches less tall lol

Also, i got a response from the maker of "Optimus", an lmtv with a habitat bolted right onto the frame who states no issues in 5 years. I dunno that is 100% accurate, but i do know that's definitely what he's claiming.

View attachment 937134

When I mounted my habitat (20ft long shipping container) I built the interface to be able to use springs or not. First I tried without springs and when twisting up on a ramp there was way too much stress and it started to bend the bottom of the container. I then install the springs and now they separate from each other up to a few inches. I would never rigidly mount a box on these.
If I had a flexier habitat I may have gotten away with it but then you have all sorts of issues related to that.

 

[Primussucks]

The wripling on the panels in this picture is my concern. Not sure whats going on here, but the seams look like they are separating...

I like the idea of composite for the clean panels, but don't want the added 'torsion' frame. for many of the reasons stated in this thread. height, torsion frame putting pressure where it wasn't designed to be.

i'm torn on what the right answer is and what direction i'm going to go. I've talked with several folks and looked at a lot of the designs, I just can't figure out how to keep the 'skin' clean and not wavy using metal.

I've think I've settled on my 'thermal transfer' solution for metal. Spray cork. Used in marine applications. I'm going to use it on the cab as well. Lots of good videos out there on this

Height and easy entry/exit are key design criteria. I don't know what it's called, but i'm calling it 'school bus entry'.

 

[MatthewWBailey]

Interesting thread read. Out of curiosity, how is the factory M1079 Van body attached?

 

[aw113sgte]

Interesting thread read. Out of curiosity, how is the factory M1079 Van body attached?

Rigid mounts in back, spring mounts in front, with some rubber pads.