Smaller trailers don’t have separate brakes, but the medium and heavy-duty trailers have either trailer disc brakes or trailer drum brakes. In most applications, the trailer brakes work via a hydraulic surge brake actuator. When you step on the brakes, the forward movement of the trailer pushes the telescopic actuator in, which activates the master cylinder and the brakes on the trailer. Purchase the proper actuator for the braking system on your trailer. If it has trailer disc brakes, the actuator needs to be for disc brakes. If the trailer has drum brakes, you need an actuator for trailer drum brakes.
Drum brakes are shaped like a moon crescent and fit inside the drum. The brakes are called shoes. When the brakes are activated, the wheel cylinders push the brake shoes away from the center of the wheel and push them against the drum, causing friction to slow the trailer. Disc brakes ride in a caliper. When you step on the brakes, the caliper pushes the brake pads against the brake rotor to cause friction, thus slowing the trailer. You can’t see the shoes inside the drum, but you can see the brake pads sitting in the caliper. You have to remove the drum to check the thickness of the shoes, but if you crawl under the trailer, you can see the pad thickness without taking the brakes apart. If you have spoked trailer wheels, you may be able to see the thickness of the pads between the spokes.Both brakes are made from composite material and usually contain asbestos to keep the temperature down. Disc brakes are better for trailers as they don’t heat up as fast as drum brakes. Heating up isn’t usually a problem unless you are towing in the mountains, going down a steep grade. Both types of brakes could suffer fade-out, but disc brakes are less susceptible to overheating and fade out because they are exposed to the air. Drum brakes are contained in a cast iron drum and do not have the benefit of air running across them to cool them down.