Whether you are adding electric drum brakes to a trailer without any existing brakes or changing from hydraulic to electric brakes, you will need some basic information to build a system that will stop your trailer safely and dependably. The following article and tables provide information about your options and will help you find parts that will work together. If you just want to find parts quickly, see our Parts Reference Table, below.
To operate the brakes, your trailer's axle must have a brake mounting flange attached behind the existing hub assembly on each side. Most axles have these, but if yours has no brake mounting flanges, you have two options:
1. You can replace the axle with a properly rated one that already has brake flanges welded in place. Ordering a new axle complete with electric brake assemblies and drums may actually cost less than buying separate parts. However, to order a complete axle you will need to know the axle capacity, wheel bolt pattern, spindle type (whether it is drop or straight) and type of brake assembly - in this case, electric. You will also need to know the distance between your trailer's springs, center to center, and between the hub faces.
2. You can purchase brake flanges and have a qualified welder weld them to the axle. When a brake mounting flange is welded to an axle, it must be welded square and concentric. This usually requires a jig to hold both parts in position. A trailer shop should have the equipment and personnel to weld brake mounting flanges to your axle.
This is the most popular brake mounting flange. It's a square, 4-bolt pattern that is used on most axles up to and including 3,500 lbs. The next-most-popular flange is the 5-bolt design, which is commonly used on 5,200-lb, 6,000-lb and 7,000-lb axles. The pattern of the holes in the flange is standard, so all you need to note is the number of holes in the mounting flange, and the axle diameter.
If your trailer axle has brake flanges and you plan to add the other brake components separately, you must select hub-and-drum assemblies that are compatible with the trailer spindles. The numbers stamped into your trailer's existing bearings and seals will help you determine the proper hub-and-drum assemblies. You will also need to know the wheel bolt pattern of your existing hubs so that the new hubs will match up with your existing wheels. If you cannot find part numbers for the bearings and seals, you can measure the spindles (see spindle diagram) at the inner (C in diagram) and outer (D in diagram) bearing surfaces as well as the seal contact surfaces (B in diagram).
This is our most popular setup for a 3,500-lb axle. Notice the tapered spindle. It uses L68149 inner bearings (dimension C) and L44649 outer bearings (dimension D). The 10" hub-and-drum with a 5 on 4-1/2" wheel bolt pattern is also pictured.
Once you've selected a hub-and-drum assembly, you can choose a compatible brake assembly. You need to know that the brake assembly is compatible with the brake mounting flange and with the drum's diameter and depth.
The labeled drum shows the measurements you need to know to select a brake assembly. For the 3,500-lb axle, the 10" brake assembly is shown. Only one size is available for a 10" hub-and-drum assembly. You'll just need to choose between self-adjusting and manual-adjust brakes.
Finally, to operate your electric brakes, you will need to set up your tow vehicle with a brake controller and the proper wiring. Our article, Trailer Brake Controller Information, explains brake controller similarities and differences, and our Brake Controller Application Guide will help you to determine all the parts needed for your vehicle.
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