Electric trailer brakes need adjustment when they stop responding evenly, drag constantly, or fail to engage
Electric trailer brakes use an electromagnet to clamp brake pads against a drum when your tow vehicle's brake pedal is pressed. Unlike hydraulic brakes, they have no fluid to bleed and no master cylinder to maintain — but they do require periodic adjustment as the brake shoes wear down. When one side pulls harder than the other, the brakes drag even when not engaged, or the brake controller shows a fault code, adjustment is usually the first step before replacing parts.
The adjustment process differs slightly between 12-volt and 24-volt systems (most trailers use 12-volt), but the principle is the same: you manually turn an adjustment screw on each brake assembly until the shoes sit at the correct distance from the drum. This is a job you can do yourself with basic hand tools, though you'll need to safely lift the trailer and remove the wheels.
Key Takeaways
- Electric trailer brakes adjust via a star wheel or hex screw on each brake assembly, not through a centralized system like hydraulic brakes.
- Uneven braking, constant drag, or a fault code on your brake controller all point to shoes that have worn away from the drum and need adjustment.
- You must adjust both sides of the trailer to the same specification, or the trailer will pull to one side during braking.
- Adjustment takes 30 to 60 minutes per axle and requires the trailer to be safely lifted, blocked, and the wheels removed.
- If adjustment does not restore even braking or the controller still shows a fault, the magnet coil or wiring may be failing and needs replacement.
When electric trailer brakes need adjustment
Electric brakes wear gradually as the friction material on the shoes erodes. As they wear, the shoes move farther from the drum, and the electromagnet has to pull harder to make contact. Eventually, the magnet cannot pull the shoes far enough, and braking becomes weak or uneven.
Watch for these signs: one wheel locks up or drags while the other barely brakes, the brake controller displays a fault code (usually a steady or blinking light), the trailer pulls to one side during braking, or you hear grinding or scraping when the brakes engage. Some trailers also have a manual slack adjuster that tightens over time and can be adjusted without removing wheels — check your brake assembly documentation to see if yours has one.
Do not ignore drag. A brake that is always partially engaged will overheat the drum, warp it, and eventually cause the magnet to fail. If you notice the trailer wheel is warm to the touch after driving, stop and adjust when ready.
Tools and safety setup you will need
Gather a socket set (usually 9/16-inch or 1/2-inch for wheel lugs), a jack rated for your trailer's weight, jack stands (at least two, one per side), wheel chocks, a flashlight, and either a star wheel adjuster tool (a small hooked tool, often included with the brake assembly) or a hex wrench (size depends on your brake model). Some trailers use a Phillips or flathead screwdriver instead.
Park the trailer on level ground, engage the tow vehicle's parking brake, and place wheel chocks behind the wheels you are not lifting. Lift one side of the trailer with the jack, then when ready place jack stands under the frame on both sides of the axle. Never work under a trailer supported only by a jack. Remove the wheel and spin the drum by hand to make sure it turns freely before you begin.
If the drum does not spin or grinds, stop and inspect for a seized brake or a bent axle. Adjusting a seized brake will not fix the problem and may damage the magnet.
Step-by-step adjustment for star wheel brakes
Most single-axle trailers use a star wheel adjuster located on the back of the brake assembly. You will see a small wheel with three or four notches, usually accessible through a hole in the brake backing plate or drum. Insert the star wheel tool into the notches and rotate it toward the front of the trailer (the direction varies by manufacturer, so check your manual — rotating the wrong way tightens the shoes against the drum and locks the wheel).
Turn the star wheel one notch at a time, then spin the drum by hand. You are looking for the point where the drum just barely drags — a slight resistance that stops as soon as you release the wheel. Once you feel that resistance, back off one more notch so the drum spins freely with no drag. This is the correct setting.
Repeat this process on the other brake assembly on the same axle. Both sides must be adjusted to the same point, or the trailer will pull during braking. After adjusting both sides, spin each drum several times to confirm they turn freely and evenly. Reinstall the wheel, lower the trailer, and test the brakes at low speed in a safe area before returning to normal driving.
Adjustment for hex screw and bolt-on brakes
Some electric brakes, particularly on newer trailers or heavier models, use a hex screw adjuster instead of a star wheel. This screw is usually located on the side of the brake assembly and can be turned with a hex wrench or Allen key. The principle is identical: turn the screw clockwise (or counterclockwise — check your manual) until the drum drags slightly, then back off one turn.
A few trailers use a bolt-on brake design where the entire brake assembly bolts to the axle and the adjustment is made by loosening the bolts and sliding the assembly closer to or farther from the drum. This is less common on small trailers but more common on commercial or heavy-duty models. If your trailer has this design, loosen the bolts slightly, adjust the assembly until the drum drags, then tighten the bolts evenly in a cross pattern (like tightening wheel lugs) to avoid binding.
After any adjustment, test the brakes gently at low speed. If the trailer still pulls to one side or the controller shows a fault, the magnet coil or wiring on one side may be failing, and that brake assembly will need replacement rather than adjustment.
Testing brakes after adjustment
Before driving on public roads, test the brakes in a safe, empty area such as a parking lot or quiet road. Accelerate to 10 to 15 miles per hour, then explore the brakes gently. The trailer should slow evenly without pulling left or right. Repeat at 20 to 25 miles per hour. If the trailer still pulls, stop and re-check your adjustment — you may have missed one side or not adjusted them equally.
Listen for grinding or scraping. A small amount of noise during the first few stops is normal as the shoes bed in, but persistent grinding suggests the shoes are worn through to the backing plate and need replacement, not adjustment. If the brake controller still shows a fault code after adjustment, the magnet or its wiring is likely faulty.
Check the brake controller display while braking. Most controllers show the amount of current flowing to each brake. If one side shows significantly less current than the other even after adjustment, that magnet is weakening and will need replacement soon.
When adjustment is not enough
If the brakes still do not work evenly after adjustment, or if the controller shows a persistent fault, the problem is not wear — it is a failing component. Magnet coils can burn out from overheating or age, especially if the brakes have been dragging. Wiring connections at the brake assembly or the trailer connector can corrode or loosen, reducing current to one side. Brake shoes can wear completely through, and drums can warp from heat.
Before replacing parts, check the wiring. Disconnect the trailer from the tow vehicle and inspect the connector pins for corrosion or bent contacts. Clean any corrosion with a wire brush and reconnect. If the fault persists, the brake assembly itself needs replacement. Most single-axle trailer brakes cost between $150 and $400 per side, plus labor if you have a shop do the work.
Do not attempt to repair a magnet coil or rewire a brake assembly yourself unless you have experience with 12-volt electrical systems. A miswired brake can fail suddenly or cause a fire in the trailer.
Frequently Asked Questions
How often should I adjust electric trailer brakes?
Adjustment frequency depends on how much you tow and how hard you brake. Most trailers need adjustment every 5,000 to 10,000 miles of towing, or whenever you notice uneven braking or drag. Check your brakes at the start of each towing season and after any long trip.
Can I adjust the brakes without removing the wheels?
Some trailers have a manual slack adjuster accessible from outside the wheel, but most require wheel removal to reach the star wheel or hex screw. Check your brake assembly documentation. If you cannot locate the adjuster without removing the wheel, you will need to lift and remove it.
What if one brake is dragging and the other is not working at all?
This usually means one magnet is failing and the other is overheating from constant drag. Adjust the dragging brake first to stop the overheating, then test the non-working brake. If it still does not engage after adjustment, that magnet coil needs replacement.
Do electric brakes need adjustment more often than hydraulic brakes?
Yes, because the shoes wear and move away from the drum, whereas hydraulic brakes compensate automatically through fluid pressure. Electric brakes require manual adjustment as they wear, typically every season or every 5,000 to 10,000 miles of towing.
Can I adjust the brakes while the trailer is connected to the tow vehicle?
No. Always disconnect the trailer, park it on level ground, and lift it safely with jack stands before adjusting. Working on a connected trailer risks the tow vehicle rolling or the trailer shifting unexpectedly.