Parts Needed to Add Electric Drum Brakes to a Trailer

idler hubTrailer hub-and-drum

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.





Parts Reference Table


Parts for Adding
Electric Drum Trailer Brakes
TrailerTruck
PartBrake Mounting FlangeSpindleBrake AssemblyHub-and-Drum Trailer WiringBreakaway KitBrake Controller
Brake Mounting Flange Spindle diagram Electric Drum Brake Assembly Straight on View of Hub Accessories for wiring a trailer for electric brakes Breakaway kit Electric Brake Controller
ConsiderAxle diameterBearing and seal dimensions
B -
C -
D -
Axle capacity -
Brake assembly diameter

Brake shoe width
Hub diameter

Hub bolt pattern
Trailer connector must match connector on vehicle Number of axles on trailer Vehicle-specific wiring may be available




Trailer Brake Mounting Flanges


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.


brake mounting flange

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.





Trailer Hub-and-Drum Assemblies


Trailer spindle diagram

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 at the inner (C in diagram) and outer (D in diagram) bearing surfaces as well as the seal contact surfaces (B in diagram).



Trailer hub-and-drumspindle

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.






Trailer Brake Assemblies


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.



Brake Assembly Drum with diameter and depth indicated

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.





Wiring a Trailer for Electric Brakes


Parts needed to add wiring to trailer for electric brakes

You will need to run wiring from the front of your trailer to your trailer brakes to carry electric power to them. In addition to wire, you may need connectors, zip-ties, wire clips, electrical tape, and ground screws. You'll also have to convert your trailer connector to a 7-way that includes a circuit for electric brakes.


Each brake assembly should have 2 wires coming out of the back. Attach one of these wires to the trailer for the ground. The other wire will receive power. It doesn't matter which wire you use for which purpose.



Diagram of power wire going to each trailer brake

Run a 10-gauge wire (which will have blue insulation) from the front of the trailer to one of the trailer brakes. This will be your power wire. Connect the power wire to the non-grounded wire on one of the brakes, then run another wire from the power wire on this brake to the brake on the other side of the axle. If you have more than 2 brakes, run power to all of them in the same way.


If possible run the wire through openings in the frame. You can also use hangers and zip-ties to route the wire. You want the wire to be close to the bottom of the trailer and not hanging down where it could get snagged or damaged.


You can use butt and quick-splice connectors to connect the wires. To help keep water out of your wiring connections, wrap them with electrical tape.


You will need to replace the 4-way connector at the front of your trailer with a 7-way that includes a connection to carry power to the brakes.





Electric Trailer Brake Controllers and Wiring


brake controller etbc7 brake wiring kit

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.



Breakaway Kits

Breakaway kit

Breakaway kits apply the trailer's brakes if the trailer becomes uncoupled from the tow vehicle. These systems include a battery and wiring, and sometimes have a built-in charger. When choosing a breakaway kit, be sure that it is recommended for use with the number of axles that have brakes on your trailer.





Common Combinations of Trailer Brake Components


Note: The following table shows common combinations of trailer components. Some trailers may have other combinations of components, so you should always verify fit before ordering replacement parts.


Typical Components by Axle Capacity for Adding Electric Drum Brakes
Axle Size EZ Lube Option Brake Flange Bearings Seal Brake Assembly Hub/Drum and
Bolt Pattern
Breakaway Kit
2,000-lb Axle

1-3/4" Diameter
Standard 4-34 Inner - L44649
Outer - L44649
10-9LH - 7" x 1-1/4"
RH - 7" x 1-1/4"
4 on 4" - 8-173-16UC3
5 on 4-1/2" - 8-257-5UC3
50-80-313
EZ Lube 4-34 Inner - L44649
Outer - L44649
RG06-020 (10-60)LH - 7" x 1-1/4"
RH - 7" x 1-1/4"
4 on 4" - 8-173-16UC3-EZ
5 on 4-1/2" - 8-257-5UC3-EZ
50-80-313
3,500-lb Axle

2-3/8" Diameter
Standard4-35Inner - L68149
Outer - L44649
58846LH - 10" x 2-1/4"
RH - 10" x 2-1/4"
5 on 4-1/2" - AKHD-545-35-K50-80-313
EZ Lube4-35Inner - L68149
Outer - L44649
10-19LH - 10" x 2-1/4"
RH - 10" x 2-1/4"
5 on 4-1/2" - AKHD-545-35-EZ-K50-80-313
5,200-lb and
6,000-lb Axle

3" Diameter
Standard4-44-1Inner - 25580
Outer -
15123 or
LM67048
GS-2125DL (10-1)
or
GS-2250DL
LH - 12" x 2"
RH - 12" x 2"
6 on 5-1/2" - AKHD-655-6-K50-80-313
Inner - 25580
Outer -
02475 or
14125A
GS-2125DL (10-1)
or
GS-2250DL
LH - 12" x 2"
RH - 12" x 2"
8 on 6-1/2" - AKHD-865-7-2-K50-80-313
EZ Lube4-44-1Inner - 25580
Outer -
15123 or
LM67048
RG06-090 (10-10)
or
RG06-070 (10-36)
LH - 12" x 2"
RH - 12" x 2"
6 on 5-1/2" - 8-201-5UC3-EZ50-80-313
Inner - 25580
Outer -
02475 or
14125A
RG06-090 (10-10)
or
RG06-070 (10-36)
LH - 12" x 2"
RH - 12" x 2"
8 on 6-1/2" - AKHD-865-7-2-EZ50-80-313

Updated by: Raymond P.

Last updated: 7/3/18







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