Torsion free subframe

[Madoxen]

Hi all i have been digging deeper and deeper into all the torsion free subframes for our pretty ugly build and have so far come up with 2 final plans all of which are not purfect but will work. Anyways while doing some more serching i stumbled accross Rvglobetrekker.com who are based in the US and sell pre made diy 3 and 4 point torsion free subframes. Has anyone here had any experiance with them ?

Also as a not on torsion free subframes i have found that the 2016 version of the zetros bodybuilders guide have direct instructions on a merc approved way of building 3 and 4 point systems , i have attached the pdf below and the relenant info starts from page 92 i think from memory. Looks like i might rethink my plans and get version number 3 signed off grrrrr

 

[DiploStrat]

That reference is pure gold. (I only question the requirement that the fixed part of a three point rig be at the rear.)

That said, many folks are a bit OCD about a "torsion free" mount. For most of us, a spring pillar mount is best as it spreads the weight across all of the frame rails. (Bimobil uses this system.)

Remember, too, that you can put a metal frame under your plastic box to provide extra strength. A badly executed three or double three (aka four) point mount can sway and can be a tremendous stress riser on the truck frame, especially on washboard.

FWIW, my truck has a double three mount, but the sub frame under the camper is so heavy, and the camper itself has a four inch foam and plywood floor, so I am not sure it is really worth it.

Advanced RV took an interesting approach with their "B-Box" adding extra rigid reinforcement within the box itself.

YMMV.

 

[Neil]

There are several ways to create a torsion free subframe. If a particular method works for you then it is clearly the right one.

We removed an existing mercedes 3 point system in favour of a rail on rail method.

Unfortunately I have seen many home built 3 and 4 point systems that don't work . They are often far to sloppy and the creators then spend endless hours trying to correct this with dampers etc.

I guess what I am saying is that unless you are a very competent engineer with lots of experience and skill ( which I havent) its is very easy to get the 3 and 4 point systems wrong.

If like me you have more limited experience and skills then it is much easier to create a very effective rail on rail system .

All are good if working correctly

Neil

 

[Geo.Lander]

From my research for my truck specifically the only approved MB torsion free subframe is a 4-point system, to which the fixed horizontal pivot is centrally mounted according the chassis squidge and articulation tests.
It is also IMO worth noting that rail-on-rail designs should not be called torsion free, as these forces are transferred to the intermediate frame and thus box in order to facilitate the spring compression, I suppose they also "bottom out" in a very progressive manner, therefore increasing the torsion as far as the travel allows. My chassis flexes a tremendous amount and I was not confident that there could be enough travel built into a spring set to accommodate for the type of terrain I aspire to travel over. It is ultimately why we decided to have the frame professionally designed and modeled in accordance with the MB chassis building guide (using finite element analysis) and built as this is far beyond my own skill set.

 

[Neil]

Geolander.

Absolutely spot on.

Your confirming my thoughts. You have opted to have it made by a qualified engineer to MB spec. It will be perfect.

My post was trying to highlight that we have seen loads of badly made 3 and 4 point systems made on a DIY basis by folks without the skills or experience ( like me )

If your going to go down the 3 or 4 point system get it right and built correctly.

Yours will be spot on I know

Neil

 

[Sitec]

I'll let you know how mine goes in a few months!

 

[Neil]

I'll let you know how mine goes in a few months!

It will be great

Neil

 

[VerMonsterRV]

That reference is pure gold. (I only question the requirement that the fixed part of a three point rig be at the rear.)

That said, many folks are a bit OCD about a "torsion free" mount. For most of us, a spring pillar mount is best as it spreads the weight across all of the frame rails. (Bimobil uses this system.)

Remember, too, that you can put a metal frame under your plastic box to provide extra strength. A badly executed three or double three (aka four) point mount can sway and can be a tremendous stress riser on the truck frame, especially on washboard.

FWIW, my truck has a double three mount, but the sub frame under the camper is so heavy, and the camper itself has a four inch foam and plywood floor, so I am not sure it is really worth it.

Advanced RV took an interesting approach with their "B-Box" adding extra rigid reinforcement within the box itself.

YMMV.

I have to say after a year and a half of travel our biggest hurdle is the size of the truck. Now this has only been in the USA and Baja so limited experience. Seems way before the roads get super rough trees/cactus/cliffs appear and stop forward progress (well guess you can add getting a 20,000lb truck stuck/damaged where assistance is tricky). Also our sway bars put a bit of a limit on downward wheel travel, great on the highway but limit wheel travel when things get uneven.

Really looking forward to seeing your build progress! Looks like you are doing a first class build.

 

[Sitec]

I have to say after a year and a half of travel our biggest hurdle is the size of the truck. Now this has only been in the USA and Baja so limited experience. Seems way before the roads get super rough trees/cactus/cliffs appear and stop forward progress (well guess you can add getting a 20,000lb truck stuck/damaged where assistance is tricky).

Australia has both situations... We have tracks that you struggle to get a standard Land Rover/Land Cruiser down, but them 200km away we have tracks that you can get a full sized truck down with ease, but the terrain is the limitation. Here's a prime example... Ian and Trish (Unimog Adventures on Youtube) testing the full ability of their Unimog on Echo Back Track here in South Australia. This is a track I want to tackle in our truck, but will be reliant on my subframe working properly to entertain it. Fingers crossed eh!! And yes, that front left wheel is off the ground!