Overrun Brake (Trailer Inertia Brake)

It is the usual brake system on braked trailers and caravans. It works mechanically, without electrical connection to the car's brakes. A breakaway cable applies the trailer brake if the trailer becomes detached. When reversing, older systems can apply the brakes; most have an automatic reverse function. Unbraked trailers have much lower weight limits.

The coupling head slides back under braking and pulls rods or cables that apply the trailer brakes.

Overrun brakes need regular adjustment and servicing like other brakes. Always attach the breakaway cable correctly around the tow bar or its eye.