A torque-free subframe for the U1300L Chassis

One of the most notable aspects of the Mercedes Benz Unimog is it's long-travel coil-spring suspension and highly flexible chassis.  The chassis can twist back and forth under extreme loads when on uneven terrain, and helps all tires stay in contact with the ground.  This torsional movement must not be transferred to the driver's cabin, or any rear-mounted beds, platforms, or boxes.  To eliminate this potential stress, the Mercedes engineers developed what they call the "torque-free subframe."  This principle is used throughout the Unimog's factory construction, for the engine, cab, and box mounting systems.   All of these components mount in such a way as to allow the chassis rails to flex around them.

The factory Pritsche (drop-side troop/cargo bed) installed on the Bundeswehr U1300L is no exception.  It mounts to a centralized rigid point on the chassis (above the rear shock and coil spring mounting location) and to two rubber-bushed pivot points - one fore, one aft of the central rigid mounting point.

My goal for the construction of this subframe was to recreate the same torque-free function, but to also incorporate a "universal" aspect which would allow for easy exchange of subframe-mounted attachments.  I wanted to keep with the Unimog tradition of "universal platform" so that I could easily swap between my expedition camper, a custom flatbed, firefighting equipment, agricultural equipment, or anything else I could dream up to adapt to the chassis.  After some consideration, I decided to fabricate the top portion of my subframe from 3"x3"x3/16" angle iron, oriented upright as a "V."  Onto the bottom of my camper frame (and future projects for this chassis,) I will have matching angle iron which will nest inside the angle iron of the subframe.  This design is self-centering and aligning, to facilitate installation of anything sitting atop the subframe.  

I first removed the Pritsche from the chassis.  From the original equipment, I retained the front and rear cross members which include the rubber-bushed pivots.  I also kept the main central saddles.  These are rubber-insulated as well and clamp to the round tube cross member which runs between the left and right rear shock/spring mounts.  Together, they form the central rigid mounting point described in the text above. 

Below, you can see how my new subframe is attached to these factory saddles...

The new rear pivot point is shown in the following image.  The chassis will flex around the bolt seen at the bottom of the steel plate...