A Complete Guide to Identifying and Maintaining Your Trailer’s Electric Brakes

If your trailer is equipped with electric brakes, regular maintenance is essential—just like the brakes on your tow vehicle. To service your trailer’s brakes properly and order the correct replacement parts, you’ll need to know how to identify the brake components and recognize common issues.
This guide walks you through identification, replaceable components, and troubleshooting tips to keep your braking system operating safely and efficiently.

Identifying Electric Trailer Brakes

1. Determining Left vs. Right Brake Assemblies

With the magnet positioned at the bottom of the assembly, the actuating arm runs from the top pivot downward toward the magnet:

• If the arm curves left, it is a left-hand brake assembly.

• If the arm curves right, it is a right-hand brake assembly.

2. Measuring Brake Size

To determine brake size, measure:

1. The diameter across the center of the shoe assembly.

2. The width of the brake shoe lining.

These two measurements define the brake size you need for replacement.

3. Flange Mount Style

Count the number of mounting holes or studs on the brake backing plate. This identifies your brake’s flange type and fitment.

4. Common Replaceable Components

Some braking issues can be fixed by replacing individual components rather than a full assembly. Common replacement parts include:

• (1) Magnet

• (2) Return springs

• (2) Hold-down springs

• (2) Primary and secondary shoe linings

• (1) Adjuster

• (1) Adjuster spring

Troubleshooting Faulty Trailer Brakes

1. Magnets

A failing magnet often causes erratic brake controller behavior. The magnet activates the brakes by gripping the inside face of the drum. Check for:

• Exposed windings

• Pinched, broken, or frayed wires

• Inconsistent surface wear

A new magnet has a flat surface. If the drum’s interior surface is uneven, the magnet may not make full contact, resulting in reduced braking performance.

2. Brake Adjustment

Brakes must be adjusted periodically, even self-adjusting brakes, which may fail to adjust properly as parts wear.
Adjustment steps:

1. Turn the adjuster until the wheel cannot rotate.

2. Back the adjuster off until the wheel spins freely.

3. A properly adjusted brake will have a slight, constant drag.

3. Adjuster & Adjuster Spring

Located below the magnet, the adjuster should turn smoothly while being held under constant spring pressure.
Common problems include:

• Seized or frozen adjuster

• Broken adjuster spring (you may hear it “rolling around” inside the drum)

• Adjuster maxed out → likely indicates worn brake shoes

If the adjuster is at its limit but the shoes are not worn out, check:

• Hold-down springs for fatigue

• Drum bore diameter to ensure it is within maximum re-bore specifications (marked on the drum)

4. Return & Hold-Down Springs

Worn or weak springs can cause:

• Excessive heat

• Brake drag

• Burning odor (“stinky brakes”)

• Shoes failing to retract properly

Return springs retract the brake shoes, while hold-down springs keep them aligned and centered. Failing springs can lead to premature brake failure.

5. Shoes & Linings

Brake shoes should wear evenly from top to bottom.
Uneven wear often indicates:

• Poor brake adjustment

• Return springs not functioning correctly