Electric trailer brakes:introduction
Electric Trailer Brake Assembly
Electric brakes are a very common and reliable means to control your trailer while towing. They are most often used on utility, equipment trailers and RVs both large and small. As the GTW for a trailer increases, the brakes are also uprated. When the time comes to repair or replace them there are many choices available. It can be confusing to decide what brakes or parts you need for your trailer.
Parts most often replaced are the shoes and magnets. They wear from use and should be inspected periodically and replaced when needed. Depending on how often you use the trailer will determine how often to inspect them. The shoes are easier to check than the magnets. You can just measure the thickness of the shoe to find out if they need to be replaced.
Magnets are harder to troubleshoot. Sometimes they quit working or will just get weak over time. To replace the shoes or magnets, look at your existing brakes. For the shoes, measure the inside diameter of the drum and the width of the shoe. This should help you to determine the correct shoes. Sometimes different weight capacity brakes will have the same size shoes. When this happens you will use the brake magnet to determine the correct replacement. Use the wires that come directly out of the magnet. The wire color will determine what exact brake you need.
Replacing the entire brake backing plate is sometimes more cost effective and easier to install than rebuilding a brake assemby. They come with new magnet and shoes already mounted on the backing plate. You just unbolt your existing plate from the brake flange, bolt on the new plate, re-connect your magnet wires and adjust. This eliminates having to take apart and rebuild the old brakes, which can be a difficult job. To determine the correct brake assembly use the methods discussed above for the drum diameter, shoe width, and magnet wire color. Also you are going to count the number of bolts that attach the backing plate to the axle brake flange.
With this information you should be able to easily determine the correct brake for your axle.
A question often asked is if the brake magnet wires are polarity specific. The magnets do not have polarity and work like a common resistor. Either wire is attached to the power and the other one is attached to the ground wire. It is recommended to run a common ground wire from the trailer plug to the magnets. The brakes should be wired in parallel, not in series.
Installing brakes on a new trailer or one that doesn’t have brakes is very straightforward. You will need to determine if the axles you have are designed to have brakes. There will be a steel plate (brake flange) welded to the axle behind the spindle. This will most often have four or five holes drilled in them. They are critical to install brakes on a trailer. If your axle doesn’t have the flanges installed it is recommended to replace the axle assembly with one that does.