OVERRIDE OR OVERRUN BRAKE COUPLINGS
On trailers between 750 kg and 2000 kg ATM (total loaded mass), braking systems that use an override principal are acceptable,
as long as they provide adequate braking for the trailer and tow vehicle combination.
The principal of this type of coupling is a sliding shaft attached to the tow ball housing of the coupling, and as the tow vehicle slows down the force of deceleration is passed through the coupling shaft and pushed either on a mechanical linkage (for mechanical brakes) or acts on a linkage connected to a hydraulic cylinder providing hydraulic pressure to a braking system (hydraulic brakes) .
This type of coupling is efficient if the ball load is not excessive and when load levelling devices are not used, as these devices impede the smooth operation of the coupling, hindering the brake performance.