I agree the trailer tongue weight had nothing to do with this failure, but I do think the trailer played a role: the trailer gives the truck something to pull against, and I don’t believe the frame could have folded up like that unless it had something trying to prevent forward motion. Remember that Newton’s first law says that objects at rest tend to stay at rest, and that an object in uniform motion tends to stay in uniform motion unless acted upon by a net external force. The trailer is the external force.
This could have happened either accelerating away from a stop, or while driving on a rough potholed road that was causing the trailer to put dynamic resistive forces on the truck. We’ve probably all felt how trailers can both push and pull on the tow vehicle under different conditions.
Imagine what would happen if you took that same truck and camper, chained the rear bumper to a big oak tree, and then tried to drive away. I believe the results would look much the same. As the pinion gear tries (and fails) to drive the ring gear, the rear axle would then rotate and lift the front of the truck up, and the frame would fail at the weakest point.
I think it’s also likely that this camper’s COG is behind the rear axle, which would help the rear axle’s attempt to lift the front of the truck.
:):)
