Mercedes LAF 1113 B family truck

Sitec

Adventurer
Whichever way you do it it'll be a great project. I was originally thinking along the lines of a rear support spring rather than a mount so the body still has support at the back, but the tail of the chassis can do as it pleases.. that said, I was pondering it in the workshop today as I contemplated pulling some stuff off my living body. So long as the cab has decent heavy rear mounts, this could be taken as 2 of your 3 or 4 points. As long as the rear 1 or 2 points were smack in the middle of the chassis rails the chassis could still flex as it pleases but carry the weight. I'm still leaning towards having a 4 point mount on mine, as I have used it as a truck off road carting rocks for our retaining when we built our house and the flex/twist off road was impressive/alarming!.... BUT, Neil's Merc (Cloud9) is testament that bolting direct to the chassis using bolts and springs also works. Guess I'll make my decision when I have a bare chassis and a body ready to fit! :)
 

Neil

Observer
My Merc has the rail on rail system , so the entire weight of the cabin is spread out over the two chassis rails. No weight as such is on bolts or mounts .

The vehicle originally had a MB 3 point system which i removed.

I was totally ignorant of the destructive nature Ripio washboard road and all my decisions at the time were based on off road chassis flex.

I now know after 15 months on the road in South America that I was ignorantly lucky in my choices and so far it has paid off.

Unless your big on long off road distances i would ( knowing what i know now ) put 75 % of my design towards combatting ripio and vibration and very little into torsion free system.

I have recently been travelling with a Dutch guy who has a GRP body on an Atego. He is 15 years on the road and has done every continent except antartica. Litterally millions of km. His vehicle has a standard chassis with no torsion combatting extras. He goes everywhere, over dunes through rivers etc.

Guess what, he has never had an issue.

I do wander if we over think things a little.

One thing i have seen here are trucks with badly made 3 and 4 point systems that are really sloppy and have had endless add ons applied to combat this. On vehicle i saw in germany had no few that about 5 big shock absorbers welded at 45 dgrees down each side. Simply exiting a roudabout sent the vehicle into an un controllable swaying motion.

If it is possible to add some adjustment into the design then this would be benificial.

Christian . Fantastic project its going to be amazing

Neil
 

Grenadiers

Adventurer
The MAN is not ours but belongs to friends of ours in Germany. We have the Swiss Saurer 6dm. Regarding washboard roads, they suck! Our cabinets just have friction ‘locks’, and they fly open on these roads. We have a tie-down system of cords holding the doors closed. We’re still figuring out how to retro-fit a solid locking system. Even the Germans push button locks came undone at times.
 

Joe917

Explorer
We also have a solid rail on rail mount. The truck has 25 years and 400000 km and no issues. We Just replaced all 6 shocks with oversized Munroe shocks, what a difference! We test drove about 50 km of washboard and it was very strange, my wife and I kept looking at the road and looking at each other with confused expressions. It looked like ripio but felt and sounded like asphalt!
We have driven with Mogs with 3 point mounts that really get a side to side "tank slapper" going on uneven terrain.
 

Neil

Observer
Regarding washboard roads, they suck! Our cabinets just have friction ‘locks’, and they fly open on
We use Southco and so far they have never failed.

However, the door on our Waeco cr 140 just fell off one day. The bottom.hinge that consists of a pin through less than 1mm of plastic gave up

Neil
 

Attachments

Christian

Adventurer
Thanks for the replies guys!

Regarding the never ending contemplation on how subframes are mounted, I just remembered what I have been driving for almost 20 years:
Landcruisers, HJ60, HJ45, HJ61 and now a HDJ 100. All vehicles with frames, and if you remove the body, the frame flexes a lot! The body actually stiffens the frame quite a lot.
Cruiser frames are riveted like truck frames.
But the design is dependant on the body to stiffen the frame, especially on the later ones.
Take the HJ45, if it's a trayback, the tray and cab will move in relation to each other. If it's a complete bus body, the body stiffens the frame accordingly.
And the bodies aren't that torsionally stiff.
If the body on a HJ61 was mounted in a 3-point pivot system, it would be hell to drive! Just a thought...

And I hear your warnings against over-engineering a 3-point system, only to end up with a vehicle that's unstable in roundabouts, not to mention an emergency maneuver!
right now I'm a bit at a loss about what I will do.

Option 1:
Attach cab and body rigidly using a subframe and connect it to the chassis using Lord cab mounts or similar.
Pro: Simple construction, no body roll, low height, will reduce noise and vibration.
Con: Will limit chassis flex and induce torsional stress in cab/body. According to the posts above this might not be such a big issue.

Option 2:
Attach cab and body subframe in front using Lord cab mounts or similar, ad pivot above rear axle with Lord cab mount incorporated.
Pro: Will allow chassis to flex, will reduce noise and vibration.
Con: More complicated, higher, may induce body roll.

Please give me more arguments, for and against.
 

Neil

Observer
As i speak i am sitting on the edge of a valley in Peru looking down into the canyon below waiting for the Dakar trucks to race through in aabout 1 hour. I will stop them and ask what they do LOL
 

Christian

Adventurer
As i speak i am sitting on the edge of a valley in Peru looking down into the canyon below waiting for the Dakar trucks to race through in aabout 1 hour. I will stop them and ask what they do LOL
I do hope you know I hate you a little bit now! ;-)

Our truck has been in Dakar, but before we got it...
a-mercedes-benz-laf-1113-at-the-dakar-rally-header-03.jpg

Let me know what they say ;-)
 

grizzlyj

Adventurer
And I hear your warnings against over-engineering a 3-point system, only to end up with a vehicle that's unstable in roundabouts, not to mention an emergency maneuver! .
A 3rd party making any sub-frame mount badly is not cool wether 3/4 point or rail on rail.
Our Mog leant a bit on bends but that's just what it did, sub frame unchanged from Mercedes.
It isn't right to say 3/4 point should be avoided if that's what Mercedes Unimogs, the "ultimate" off road truck has used for decades. Some folk might not like how it behaves but YMMV.
When the MAN Kat 1 trucks were being designed the consortium including MAN settled on a very rigid chassis, their opponants, Mercedes and Porsche, made a flexing chassis. The only reason the flexing chassis was ruled out was in the early design one criteria was the trucks should float. Thats why a Kat 1 cab, engine, battery compartment and fuel tank are all one unit, they did have a sealed under tray to make the whole thing bouyant. A truck bed including the in water propulsion was to be added when needed, but supposedly with a flexy chassis they couldn't get the rear bed to stay water tight. So, if you want the truck to float have a super stiff chassis and probably rail on rail. If floating is less of a priority then 3/4 point or rail on rail, just do it properly :)
 

Neil

Observer
Grizzly

Totally agreed. The problwm is finding an expert. I personally think that its easier to completely screw up a 3 or 4 point system by getting it wrong than a rail on rail system . I actually think that a a good 3 or 4 point system is by far the best , if it right.
I have seen more bad ones than good ones thats for sure. I wouldnt have a clue how to design a good one

Neil
 

Sitec

Adventurer
As i speak i am sitting on the edge of a valley in Peru looking down into the canyon below waiting for the Dakar trucks to race through in about 1 hour. I will stop them and ask what they do LOL
Very jealous! Did you see the Iveco go through with it's back left wheel on fire? :)
 

Christian

Adventurer
Hi guys! A truck like ours with a fully integrated camper and cab just popped up for sale!

MB 911 on Mobile.de

I have no idea about how they have done it, but I’ll try and contact them to pick their brains.

It looks like it does well in moderate terrain and it seems like they have tamed the flexible chassis:

918289A2-539C-4EBB-9576-61E0586838B4.jpegBB76125D-150A-43B7-9226-CA3B9DEC5FD7.jpegF83B02B5-9099-49FB-970C-DEFCD95D6C03.jpeg8D00294C-0E34-4EE0-AC87-7F5063F18CD0.jpeg5DFB58AB-8700-4051-9BCB-47DB50C2D3B9.jpeg
Look at the flex on the others!
 
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