That looks like the hydraulic wheel cylinder and return spring from a drum brake that's somewhat larger than the one in the picture, set up to actuate something within the brake through the sort of torque shaft and lever that's normally used to actuate the 'snail cam' in air operated drum brakes for trucks.
I too have never seen anything quite like the device in the picture.
It appears that the axle is rigidly bolted to the frame through the plates shown.
A serious vehicle manufacturer would interpose some kind of spring or bumper in order to limit the forces applied to the frame at any speed; I infer that the assembly was put together by an amateur, or possibly an agricultural manufacturer, where the design speed is assumed essentially zero.
Mike Halloran
Pembroke Pines, FL, USA