You may be considering adding electric over hydraulic drum brakes to a trailer without any existing brakes or converting from electric drum to hydraulic drum brakes for improved stopping power. If so, you will need some basic information to build a system that will stop your trailer safely and dependably. The article and Parts Reference Table below provide information about your options and will help you find parts that will work together, including electric over hydraulic brake actuators. If you just want to find parts quickly, see the Table.
Electric over hydraulic brakes can give you a better braking system for your trailer than either straight electric or hydraulic brakes alone. Electric trailer braking systems provide fast response times and good control over the action of your trailer brakes, but they don't provide as much stopping power as hydraulic brakes. They include an electric brake controller that mounts inside your cab so you can conveniently control the action of your brakes. You can easily adjust your brakes to match the load you're towing.
Hydraulic braking systems can provide stronger stopping power than electric brakes but can be slower to apply. They can't be adjusted to match the load you're carrying. And they rely on a surge actuator that is built into the trailer coupler and that compresses when the tow vehicle slows and the trailer pushes against it. A delay occurs between the time the tow vehicle brakes are applied and the time the actuator applies the trailer's brakes. This delay can be longer than that of electric brakes. Also, you have to lock out a typical surge actuator (which normally requires you to get out of your vehicle) so that you can back up the trailer. You don't have to do anything special to be able to back up a trailer that has electric brakes.
With an electric over hydraulic brake setup, you get the best of both worlds - the great, smooth braking control that an electric brake controller provides and the stopping power of hydraulic brakes. Also, backing up will never be a problem. To set up electric over hydraulic brakes, you wire the tow vehicle for electric brakes and install hydraulic brake lines and brakes on the trailer. An electric over hydraulic brake actuator provides the key to go between the two types of systems. This type of actuator usually mounts on the trailer. It receives electric signals from the tow vehicle's brake controller and applies pressure to the trailer's hydraulic brake lines. With an electric over hydraulic braking system, you get the control and response time of electric brakes combined with the stopping power of hydraulic brakes.
If you install electric over hydraulic brakes, you can choose between hydraulic drum or disc brakes. Generally, disc brakes provide stronger braking action than drum brakes, which reduces stopping distance and increases your safety. Also, disc brakes require less maintenance than drum brakes because they have fewer moving parts.
For brakes to operate properly, your trailer's axle must have a brake mounting flange attached behind the existing hub assembly on each side. Most axles have these, and if your trailer aready has brakes, it will. But if your trailer 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 hydraulic drum 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 diameter, wheel bolt pattern, spindle type (whether it is drop or straight) and type of brake assembly - in this case, hydraulic drums. 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 qualified welders to weld brake mounting flanges to your axle.
Pictured 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 axle diameter and the number of holes in the mounting flange.
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. For help with determining wheel bolt pattern, see our article, Determining the Bolt Pattern of Your Wheel. 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, you can choose a compatible hydraulic 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 that you need to know to select a brake assembly.
Next, you will need a brake line kit to plumb the trailer from the electric over hydraulic actuator to the drum brake assemblies. Brake line kits are selected according to the number of axles on the trailer. If your trailer has a torsion axle, you will need to get a brake line kit that includes flexible lines to the brake assemblies. This will allow the line to flex with the movement of the axle.
Next, you will need to select an electric over hydraulic actuator that is compatible with drum brakes and that installs on the tongue of the trailer frame. Kits with plug-in connectors are available and make installation much easier. Some electric over hydraulic actuators include breakaway kits. Most don't come with breakaway kits, but they will work with standard breakaway kits that are made for electric brakes.
Finally, to operate your electric brakes, you will need to set up your tow vehicle with a brake controller and the proper wiring. A few actuators come with a portable or remote brake controller that communicates with the actuator by radio waves and plugs into a cigarette lighter or power outlet in the cab of your tow vehicle. A remote brake controller lets you easily switch between different tow vehicles to pull the same trailer. You need to make sure that any brake controller that you are considering is compatible with electric over hydraulic actuators. 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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