Allrad-LKW-Gemeinschaft

Hello Freunde.

I apologize for writing in english, but my german is simply not good enough for writing.
We have finally bought the LAF 1113 B we have wanted for years! a 1979 with 4.2m with long doka and servo.
I have been reading, asking questions and planning for years since we sold our Volvo TGB 1314 6X6.

And one thing keeps me awake:
We want to include the cab in the living area. It just suits us better.

I have read almost all the posts I have been able to fing here on "lagerung", "rautenlagerung" "federlagerung", "kurzhauber" etc. and aufbaurichtlinien from 1977 and 1984 (That was the ones I could find using Pirx' link) and I have looked all over the webb, have seen the pictures of both Kurzhaubers, 1017's, Unimogs etc. twisting like crazy.
I do have some experience since I have driven Unimogs, Magirus and MAN 4X4 trucks in the army.

But I do believe my plan can be done! Please help me!

Having looked at how it comes from the fire department makes me wonder: (Excuse the crude drawing)
There's in effect two separate frames on top of the chassis with the springs/tellerfederung tightened so hard, there's hardly 10mm's of movement possible. The frames separate just behind the cab.
In my mind that leaves very little room for frame flex, and concentrates it in one spot, right behind the cab.
I can come up with a few reasons why it was done so:
1: A fire truck will not see hard terrain, so a more flexible solution was not needed?
2: The service life of a fire truck includes very few kms, so the stress on the components was acceptable?

For our use there's a few things I would like to do better:
1: As mentioned we want to integrate cab and box.
2: To isolate cab and box from the frame to minimise noise and vibration.
3: Spread stress along the frame
My idea is to make a subframe extending original cab, somewhat like it was done by the builder, but all the way needed for the camper.
Then I plan to use cab mounts/silentblocks and start where the original cab mounts are.
Longer back I would make a hybrid mount using a cab mount but with a longer bolt and put a spring on the bottom. This would keep the cab/camper securely attached while vibration isolated and at the same time allow the frame to flex in terrain. Furthest back I would like to use a vippe like in a 3-punkt lagerung and incorporate either cab mounts or a usable rubber/poly bushing.
But it would have to have enough vertical movement to account for the springs when flexing... Have to think about that some more!

What do you think?

Hi Christian,

have lots of fun with your mercedes

Regarding your question:

I think the 3 point mount behind the rear axle is rather useless since the frame does not bend anymore behind the rear spring mount.
The main point of your construction ist the integration of Doka and Cabin. First, this cage has to be stable enough to resist the twist of the frame, independent of the mounting. Second, the mounting points have to be stable enough to keep the cage on the frame even when twisting.
The Magirus way of setting up an integrated structure on an awd chassis was to separate hood and wings from the rest and built a classic 'Federlagerung' for the rest of the structure. Unless you do not want to keep the frame from twisting, this might be the best way

Best
Uwe

Hi,

before you Start a project and are serious about it , you Need to know your specification /what you want to achieve. This Plan will Give you an idea How much resources you Need.
With this topic, you can fill a book.
It’s like Building a House, you need to know your real estate and its properties before you start with the basement.

1. what have you specified in regards to Axel articulation
2. how much overall hight am i willing to give up
3. how much Stress is my Upper Strukturen able to handle
before damaging ( >elastic deformation)
4. ..... aso

Uwe hat geschrieben: ↑

2018-09-10 13:20:08

Hi Christian,

have lots of fun with your mercedes

Regarding your question:

I think the 3 point mount behind the rear axle is rather useless since the frame does not bend anymore behind the rear spring mount.
The main point of your construction ist the integration of Doka and Cabin. First, this cage has to be stable enough to resist the twist of the frame, independent of the mounting. Second, the mounting points have to be stable enough to keep the cage on the frame even when twisting.
The Magirus way of setting up an integrated structure on an awd chassis was to separate hood and wings from the rest and built a classic 'Federlagerung' for the rest of the structure. Unless you do not want to keep the frame from twisting, this might be the best way

Best
Uwe

Thanks Uwe!

I think you are right, and the more i think about the 3rd mount, the more I realize it is either unneccesary, or extremely complicated to do, if it should work correct with the cab+spring mounts.
Besides, the cab mounts should be sufficient to keep everything in place, that is what they are made for. So the best way may be to contact a manufacturer of cab mounts and ask them.
Just have to figure out the approx. weight of the cab and box....

I will look in to separating hood and wings, but it might not be necessary, they are really short.

sascha71 hat geschrieben: ↑

2018-09-10 15:29:40

Hi,

before you Start a project and are serious about it , you Need to know your specification /what you want to achieve. This Plan will Give you an idea How much resources you Need.
With this topic, you can fill a book.
It’s like Building a House, you Need to know your real estate and its properties before you Start with the basement.

1. what have you specified in regards to Axel articulation
2. how much overall hight am i willing to Give up
3. how much Stress is my Upper Strukturen Able to handle
Before damaging ( elastic deformation)
4. ..... aso

Hi Sasha

True, and I have built my own house actually ;-)
I can't answer the questions with numbers or hard facts yet, but they are all things I have considered and thought alot about.

1. I have seen how much the frame can flex (and have pictures, but I think it's not allowed to post them?).
But that does not mean that it should be allowed to do so under all circumstances.
2. The hope is to have a flat floor straight from the cab to the camper, that's the main criteria.
3. I can't answer that, and I do not even know where to find that information. I think a GFK box will be the way to go, but any idea of the strenght of that, or the stress and forces coming from the frame is almost pure guesswork for me.

Hi,

for starters, axle articulation, very simple, between axle and axel, what angular difference
have you specified?
Means, how high can ohne wheel ( axle 1) climb on a slope while the other wheels (axle 2) remain horizontal.

sascha71 hat geschrieben: ↑

2018-09-10 18:46:01

Hi,

for starters, axle articulation, very simple, between axle and axel, what angular difference
have you specified?
Means, how high can ohne wheel ( axle 1) climb on a slope while the other wheels (axle 2) remain horizontal.

Hi, and thanks for your reply!

I have not made any specifications.

But let's say I did, i.e. 30 degrees. Correct me if I'm wrong, but how that would affect the frame depends on axle distance, weight, softness of springs, antiroll bar, hardness of antiroll bar etc. before it even affects the actual frame, or have I misunderstood something?

If it was just how much the frame twists, and how much that affects the length of springs in "federlagung", I can make an approximate calculation, like 15 degrees means approx 15cm of spring travel at most.

I'm trying to learn, so please be patient with me.

Hi,

30* / >1m ramp is a number, if we keep it very simple and take a 4,2 m wheelbase, the twist of the Frame between front fixation cab and the end of the Frame will be approx >400mm Static/without any suspention travel involved.

Dont expect too much Travel capabilities from your 911/1113 Suspension.

For example, my own 911 ( tosion bar / original springs ) is specified with 20* (static) with my specification the cab/Box has ~180/240mm Offset capabilities not corporating the flexible portion. ( safety )

Any restriction in travel will go into the top structure and/or restriktiv suspension(frame) travel, reducing traction. To deal with the issues will drive wheight and/or Overall hight to the vehicle

If i have time ,I can give you the exact number.

But again, you can write a book on this topic, all depending ..... I am not saying that Something else will not work, but if you want to make sure .....

My recomendation:

Take steeltubing (typical bus) restrikt/ eliminate movment between frame and top hat and change suspension.
do not use stiffening Elements in your top strukture such as stiff isolation ( noise) or walls. Ridgid formation such as windows aso. need to have enough clearance to move.

if you need more details,

... Gilbert had built what you want, an Mercedes 911 with busbody on ... may bee you find the storry somewhere in internet ... as i remember the connection between frame amd body was very very complicated ...

... have you tested out torsion with the original setup? ...

Gruss Ulf

Hi Christian,
If You took the pictures yourself, you can post them here, unless...

they are too big... (<1MB).

Regards, Härry.

@Ulf, hatte Gilbert nicht den Airstream auf den KAT montiert??

... beim Airstreamkat ist mir keine Beteiligung von Gilbert bekannt, ich habe aber bei Weiten nicht alle seine Projekte mitverfolgt ... beim Kat mit seinem verwindungssteifen Rahmen ist ein integrierter Aufbau ziemlich einfach zu realisieren ... dummerweise steht dann der Mittelmotor direkt im Wohnzimmer, aber irgendwas ist ja immer ...

Gruss Ulf

Hi,

axel to axel difference = 20* ( axel articulation/ no weight/suspension) , deviation in hight from cab fixpoint to end off frame ( marks ) = 446mm. (4,2m/911/1113 only)

First of all, I really need a thumbs up button to each of you, thanks for your replies!

Sasha71, thanks for your detailed reply and calculations. I really appriciate you take the time to help me!

I have thought about using steel framing, my main issue is cold bridges, wheight and rust (in that order).
I have mainly considered either plywood (with fiberglass + epoxy over) like a boat hull, or GFK sandwichplatten for the above reasons.
GFK sandwich can flex, just look at a kühlkoffer going over a curb
But I might reconsider...

I have thought about suspension, and wondered why that is not more often debated? When we built our Volvo TGB 6X6 one thing we spent a lot of time looking at was suspension.
The suspension should be tuned for the weight of the vehicle, and I'm suprised I have not read about reducing the stiffness of the springs, when going from 12T to 7.5T

Ulf, Thanks! I have not found Gilbert, but an old link to Sandblech, wasn't that the kurzhauber with the old Zetra bus body? I loved the project, but lost touch, did it get finished?
I have seen several more tradidtional buses and written with BasisCampBerlin.de, who has a bus. They advised me to use a 3-point system...
And I admit I haven't tested it, but that does flex between the cab and fire body, which I wish to eliminate...
Regarding Airstrem KAT, someone suggested using a bus configuration and move the engine all the way to the back. Too much for me though!

DäddyHärry, I know, they are not mine, and I have been cautioned once....
(Btw only forum I have experienced that...)

Sasha71, your numbers and drawing actually shocked me! I need to find a proper drawing of the frame to do some sketches...

Thanks again guys!

... yes, it was the project with Setra bus body ... Sandblech is also correct, laterone these side moved to eisenzelt, but these ist also down, so far i know ... I have no information if the project was ever finished ... but eht pictures show quite well the problem what you have to solve ...

Gruss Ulf

Hi Ulf, all the pictures are gone, and the youtube video too. So i fear the project was never finished...

Based on some of your recommendations, I have come up with an alternate idea, keeping the 3-point system, but making better room for the frame.
Please note that these are just scethces, and no measurements are remotely accurate, just a test... The idea is to keep the silent blocks up front, and have a 3-point system in front of the rear axle (with silent blocks included, but not shown here), to minimize the amount of flex exerted at this point.
The reason for this is to minimize the needed clearance around the frame. And for the same reason there are no subframe or other parts between the camper box floor and the frame right out back.
Again, the goal is to integrate cab and camper box, while minimizing noise and vibrations in the entire system.

Has nobody seen something like this?

Hey,

to be honest i would fear this construction will cause a terrible drivability on streets. Due to the "Wippe" in the middle youre body will lean heavily in curves.
So does my "Einheitskoffer" with this mount in the front of the box and two fix mounts in the rear. But youre body will be far more topheavy and even longer.

If you want to construct with that much effort i would use two "Wippen" perpendicular to yours above each framerail at the front of the box - and one orientated like yours at the end of the frame or above the rear axle.

Further i would beef up the front rubber mounts for some that can take more load and more flex.

Greets

Freddy

Thanks Freddy!

I agree that especially round-a-abouts would be really bad.
I saw one who stabilized the rear using airbags between the chassis frame and subframe. The idea was to keep them inflated on the street, and deflate in heavy terrain to allow the chassis frame to flex.
That might be a simple solution.

I am not sure what you mean with the perpendicular wippen, like rautenlagerung?

I have found rubber mounts that takes up to 750 kg each. And they can be installed parallel sharing load.

It is a bit of a paradox that stabilisator is so hard, that the suspension doesn’t flex, and tge frame does it instead.

I am thinking about softening the suspension to better suit the actual load.