How to Adjust Electric Brakes on a Trailer

Electric trailer brakes don't self-adjust the way drum brakes on a tow vehicle sometimes do. If you've noticed your trailer pushing your tow vehicle, brakes that grab too hard, or uneven stopping, there's a good chance the system needs adjustment — either at the brake controller, the brake magnets themselves, or the mechanical components inside each drum. Here's how the process works.

How Electric Trailer Brakes Work

Electric trailer brakes use an electromagnet mounted inside each brake drum assembly. When you apply the brakes, your tow vehicle's brake controller sends a voltage signal through the trailer's wiring harness. That voltage energizes the magnet, which grabs the inside of the rotating drum and activates the brake shoes.

The strength of braking force depends on two things working together:

• The brake controller's gain setting — how much voltage it sends to the magnets
• The mechanical adjustment of the brake shoes — how close the shoes sit to the drum surface

Both matter. You can have a perfectly calibrated controller and still have weak braking if the shoes are worn down or adjusted too loosely.

Step 1: Check the Brake Controller Gain Setting First

Before touching anything mechanical, start with your brake controller. Most controllers have a manual override lever or button that lets you apply the trailer brakes independently of your tow vehicle's brakes. Use this to feel what the trailer brakes are doing on their own.

Setting gain (output level):

• Start with gain set low
• Drive at a slow speed (around 25 mph) on a safe, open road
• Manually activate the trailer brakes using the override
• Increase gain until the trailer wheels just begin to lock up, then back off slightly
• That's your baseline

The goal is firm, controlled braking without the trailer wheels skidding. Too little gain and the trailer pushes. Too much and the trailer jerks or the wheels lock. ⚖️

Brake controller gain is not a set-it-and-forget-it number. It changes with load — a fully loaded trailer needs more gain than an empty one.

Step 2: Adjust the Brake Shoes Mechanically

The brake shoes inside each drum must be properly adjusted to sit close enough to the drum surface to engage quickly when the magnet activates. If there's too much gap, the brakes will feel weak or delayed regardless of controller gain.

What you'll need:

• Jack stands
• Wheel chocks
• Brake spoon (adjuster tool) or flathead screwdriver
• Flashlight

General adjustment process:

1. Safely lift and support the trailer — chock the wheels that remain on the ground, then jack up one axle side at a time
2. Remove the rubber access plug on the back of the brake backing plate — there's usually a small hole positioned near the adjuster wheel (also called the star wheel)
3. Insert a brake spoon or screwdriver through the access hole to engage the star wheel
4. Turn the adjuster to expand the shoes outward toward the drum — rotate until you feel drag when spinning the wheel by hand
5. Back the adjuster off 5 to 10 clicks until the wheel spins freely with only slight resistance
6. Repeat on every wheel — all wheels on an axle should be adjusted equally

On a tandem-axle trailer, do all four wheels. Uneven adjustment creates uneven braking, which can contribute to trailer sway.

Step 3: Inspect the Magnets and Shoes While You're In There 🔍

Mechanical adjustment only works if the components are still serviceable. While the wheel is off the ground, take a look at:

• Brake magnets — the face of the magnet should be smooth and make full contact with the drum's inner surface. A grooved, glazed, or cracked magnet won't engage properly
• Brake shoes — shoes with less than 1/8 inch of lining remaining, or that show uneven wear, should be replaced before adjusting
• Drums — scored or heavily worn drums reduce braking efficiency and may cause the magnet to grab inconsistently

Worn magnets are one of the most common causes of electric brake underperformance. A magnet that's lost its flat face creates an air gap that voltage can't fully overcome.

Variables That Affect How You Adjust

No two trailers are set up exactly the same. These factors shape what adjustment looks like in practice:

An older trailer that hasn't been maintained will often need new brake components before adjustment makes a meaningful difference. Adjustment is most effective when the underlying parts are in acceptable condition.

What Happens If the System Stays Out of Adjustment

Brakes adjusted too loose cause the trailer to push the tow vehicle under hard stops — putting added stress on the hitch and tow vehicle brakes. Brakes adjusted too tight cause drag, accelerated shoe and drum wear, and heat buildup during long trips. Either condition reduces the effective braking distance of the whole rig.

The adjustment process itself is straightforward, but what's correct for your specific trailer — its axle count, brake type, load, and controller — depends entirely on your setup and how the components are wearing.