The neck of the trailer is two pieces. The front section with the hitch attachment is a separate piece. It is made to slide on a ledge into the back half of the neck. A master cylinder for the brakes is mounted to the back half of the neck and has a rod extending from the master cylinder to the front half of the neck. As the vehicle moves forward, the weight of the load will extend the two pieces, due to the load.
Applying the Brakes
When the towing vehicle's brakes are applied, the tow vehicle starts to slow and the centrifugal force causes the trailer and its load to push forward on the neck of the trailer, which in turn forces the front half of the trailer neck in. When the front neck is pushed into the back half, the rod is pushed into the master cylinder, which then applies the brakes. When the towing vehicle releases the brakes and moves forward, the neck once more extends and releases the brakes. The rod for the master cylinder can be adjusted to cause the brakes to come on sooner or later, whichever is desired.
Trailers with Surge Brakes
A trailer with surge brakes cannot be backed up without inserting a pin in the neck of the trailer. When the tow vehicle is in reverse, pushes in on the trailer neck, which would activate the surge brakes. Inserting a pin in the neck of the trailer prevents this from happening while the driver is backing up. If the pin is left in the neck of the trailer, the surge brake will be disabled. The pin must be removed when the vehicle is ready to travel.