Electric brakes need adjustment when they stop responding evenly or drag constantly
Electric trailer brakes use an electromagnet inside the brake drum to create stopping force when you press the tow vehicle's brake pedal. Unlike mechanical brakes, they don't wear down the same way—but they do need adjustment when the magnet loses its grip or when the brake shoes drift out of position. The two adjustments you'll make are brake gain (how hard the brakes clamp) and brake shoe clearance (how close the shoes sit to the drum when not braking).
Most adjustments happen at the brake controller mounted inside your tow vehicle, not at the trailer itself. The controller is a small box that converts your brake pedal pressure into electrical current sent to the trailer. If the brakes feel weak, you turn up the gain. If they drag or overheat, you turn it down or adjust the shoes at the trailer. This is not a one-time job—electric brakes need checking every season or after heavy towing.
Key Takeaways
- Brake gain adjustment on the controller inside your tow vehicle controls how much electrical power reaches the trailer brakes, and turning it up makes them stronger.
- Brake shoe clearance at the trailer itself must be checked and adjusted so the shoes sit 0.5 to 1 inch away from the drum when brakes are off, or they will drag and overheat.
- A test drive on an empty road with light braking will show you whether the problem is weak brakes (adjust gain up) or dragging brakes (adjust shoes or gain down).
- Electric brakes need a working ground connection from the trailer to the tow vehicle, so a corroded connector or broken wire will make them fail completely.
- If the brakes lock up suddenly or feel spongy, the problem is usually a bad brake controller or a wiring fault, not the shoes themselves.
Understanding how electric brake controllers work
The brake controller sits under the dashboard of your tow vehicle and receives two signals: one from your brake pedal (telling it you are braking) and one from your vehicle's weight sensor or a manual dial (telling it how hard to brake). The controller then sends electrical current down the trailer wiring to energize the electromagnets in each brake drum.
The strength of that current is called brake gain or sensitivity, and it is the first thing you adjust. A gain setting of 5 means the electromagnet pulls with moderate force; a setting of 10 means maximum force. If your trailer brakes feel weak—the trailer keeps rolling when you brake—you increase the gain. If the brakes feel too strong and lock up the wheels, you lower it.
The controller also needs a solid ground connection. This is usually a black wire bolted to the frame of your tow vehicle. If this connection is loose, corroded, or missing, the controller cannot complete the circuit and the brakes will not work at all. Check this connection first if the brakes suddenly stop responding.
Adjusting brake gain at the controller
Locate your brake controller—it is usually mounted under the dashboard on the driver's side, near the steering column, or on the firewall. Most controllers have a dial or a series of buttons labeled "Gain," "Sensitivity," or "Boost." Some newer controllers are digital and require you to scroll through a menu using arrow buttons.
Start with a test drive on an empty road or parking lot. Accelerate to 20 mph and brake gently. The trailer should slow smoothly without locking the wheels or skidding. If it does not slow enough, the brakes are too weak. If the wheels lock or the trailer skids sideways, the brakes are too strong.
Adjust the gain in small steps—usually one or two clicks at a time—and test again after each change. Write down the setting that feels right so you can return to it if something changes later. Most trailers work well at a gain setting between 6 and 8, but this depends on the trailer weight, the brake drum size, and how the controller is wired.
If you reach maximum gain and the brakes still feel weak, the problem is not the controller—it is either a bad brake coil inside the drum, a wiring break, or a ground fault. If the brakes lock up even at minimum gain, the brake shoes are probably dragging and need clearance adjustment at the trailer.
Checking and adjusting brake shoe clearance
Brake shoes sit inside the brake drum and are held away from it by springs. When the electromagnet energizes, it pulls the shoes outward against the drum to create friction and stop the wheel. If the shoes drift inward or the springs weaken, they will drag against the drum even when the brakes are off, causing heat buildup and battery drain.
To check clearance, you need to remove the brake drum. This requires jacking the trailer safely on level ground and supporting it with jack stands—never work under a trailer supported only by a jack. Remove the wheel and the bolts holding the drum, then slide the drum off the axle. You should see the brake shoes inside, held by springs on either side.
Measure the gap between the shoe and the drum at the widest point. It should be between 0.5 and 1 inch. If it is less than 0.5 inch, the shoes are too close and will drag. If it is more than 1 inch, the brakes may feel weak because the shoes have to travel too far to reach the drum.
To adjust clearance, locate the adjustment bolt or star wheel on the back of the brake assembly. Turning it clockwise moves the shoes outward; turning it counterclockwise moves them inward. Make small adjustments—usually a quarter turn at a time—and recheck the gap. Once the gap is correct, reinstall the drum and wheel, lower the trailer, and test the brakes again.
Diagnosing common electric brake problems
If the brakes work on one side of the trailer but not the other, the problem is usually a bad brake coil or a wiring break on the silent side. Each brake drum has its own electromagnet, and if one fails, only that wheel will stop working. You can test this by jacking the trailer and spinning each wheel by hand while someone applies the brakes—the wheels should resist equally.
If the brakes feel spongy or delayed—they take a moment to engage after you press the pedal—the controller may be failing or the wiring may have a poor connection. Check all connectors at the controller, at the trailer plug, and at the frame ground. Corrosion inside a connector can block current flow and make the brakes unreliable.
If the brakes overheat and smell like burning metal after a long downhill drive, the shoes are probably dragging. This is a sign that clearance is too tight or the springs are weak. Overheating can damage the brake coils and the controller, so fix this when ready—do not ignore it and hope it goes away.
If the brakes lock up suddenly or the trailer skids, the controller may be sending too much current, or a brake coil may be stuck in the energized position. This is a safety hazard. Stop towing when ready and have the controller and brake coils tested by a trailer shop before you drive again.
Wiring and ground connections that affect brake performance
Electric brakes require a complete circuit: power from the tow vehicle battery, through the controller, down the trailer wiring, through the brake coils, and back to ground. If any part of this circuit is broken or corroded, the brakes will fail partially or completely.
The most common failure point is the ground connection. This is usually a black wire bolted to the frame of your tow vehicle, often near the battery or under the driver's seat. Over time, this connection can loosen, corrode, or be accidentally disconnected. Check it by looking for a loose bolt, green or white corrosion on the terminal, or a wire that has been cut or pinched.
The trailer connector—the plug where the trailer wiring meets the tow vehicle—should be clean and dry. If it is corroded, wet, or loose, the brakes may work intermittently. Unplug it, inspect the pins for corrosion, and clean them with a dry cloth or a contact cleaner. If the pins are damaged or the connector is cracked, replace the entire connector.
The wiring inside the trailer can also fail. If the trailer has been in an accident, the wiring may be pinched or cut. If the trailer is old, the insulation may have cracked and exposed the wire to moisture. A broken wire will stop one or both brakes from working. If you suspect a wiring problem, have a trailer shop use a multimeter to test continuity from the connector to each brake coil.
When to seek professional help
Adjusting brake gain and checking shoe clearance are tasks most trailer owners can do themselves with basic tools and a safe place to work. However, some problems require a trailer shop with specialized equipment.
If the brakes do not respond at all, even after you have checked the ground connection and the controller settings, the brake coils may be burned out or the wiring may be broken inside the trailer. A shop can test the coils with a multimeter and trace the wiring to find the break. If the controller itself is faulty, it will need to be replaced—controllers usually cost between $200 and $500 depending on the model.
If the brakes lock up or feel unpredictable, the controller may need recalibration or replacement. Some controllers have internal settings that can only be adjusted with a diagnostic tool. A shop can also test the brake coils to see if one is stuck or failing, which would require replacing the entire brake assembly on that wheel.
If you are not comfortable jacking the trailer, removing the brake drum, or working with electrical connections, a shop can do these tasks for you. The cost is usually $100 to $200 per wheel for brake shoe adjustment and inspection, plus the cost of any parts that need replacement.
Frequently Asked Questions
How often should I adjust electric brakes on my trailer?
Check brake gain and shoe clearance at least once a year, or before any long towing trip. If you tow frequently or in mountainous terrain, check every six months. Brake shoes wear slowly, but clearance can drift out of adjustment quickly if the springs weaken.
Can I adjust electric brakes without removing the brake drum?
You can adjust brake gain at the controller without touching the trailer. However, you cannot check or adjust brake shoe clearance without removing the drum. If you suspect dragging brakes, you must remove the drum to measure the gap and adjust the shoes.
What should I do if the brakes work when the trailer is empty but fail when it is loaded?
This usually means the brake gain is set too low for the heavier load. Increase the gain by one or two clicks and test again. If the brakes still fail under load, the brake coils may be weak and need replacement, or the controller may not be powerful enough for your trailer weight.
Why do my electric brakes smell like burning metal?
Burning smell means the brakes are overheating, usually because the shoes are dragging against the drum. Stop towing when ready and check the brake shoe clearance. If the gap is too tight, adjust it outward. If the smell returns, the brake coils may be damaged and the brakes need professional inspection.
Can a bad ground connection cause the brakes to work on only one side?
A bad ground will usually affect both sides equally or cause complete brake failure. If only one wheel is braking, the problem is a bad brake coil, a wiring break on the silent side, or a corroded connector pin on that wheel. Check the wiring and connector on the side that is not working.