the Marchetti trailer braking system, The braking system is implemented through an inertia system: during deceleration, the trailer wheel advances, applying the controls that actuate the drum brakes on the wheels.

http://www.vesparesources.com/50-sidecar/26364-e-uno-stabil-marchetti-originale
http://www.lancia-ardea.it/OldSite/Rimorchi.html