Electric brake adjustment basics
Electric trailer brakes use a brake controller mounted in your tow vehicle to send power to electromagnets on each wheel, which press brake shoes against the drum. Adjusting them means changing how much braking force the controller sends and ensuring the brake shoes sit at the right distance from the drum. You will do this work at your trailer, not inside the vehicle.
Most adjustments fall into two categories: changing the controller sensitivity (how aggressively the brakes respond to your tow vehicle's braking), and adjusting the brake shoes themselves so they engage smoothly without dragging. A dragging brake wastes battery power, overheats the drum, and wears shoes faster. A brake that does not engage hard enough will not stop the trailer when you need it to.
You will need a wrench set, a screwdriver, jack stands, and the trailer manual for your specific brake model. Different manufacturers use slightly different adjustment mechanisms, so checking the manual first saves time and prevents damage.
Key Takeaways
- Electric brake adjustment happens in two places: at the brake controller inside your tow vehicle (sensitivity) and at each brake assembly on the trailer (shoe clearance).
- Brake shoes should sit 0.010 to 0.015 inches from the drum when at rest; too close causes dragging, too far causes weak braking.
- The brake controller dial or switch controls how much power reaches the brakes when you press the tow vehicle's pedal, and turning it up makes braking stronger.
- If one wheel locks up before others during braking, that brake assembly needs adjustment or the controller setting is too high.
- Uneven braking or a burning smell means stop when ready and check all four brake assemblies before towing again.
Adjusting the brake controller in your tow vehicle
The brake controller is a small box mounted under the dashboard or on the steering column, with a dial or digital display. It sends a signal to the trailer brakes whenever you press your vehicle's brake pedal. The adjustment dial or buttons control how much electrical current flows to the trailer brakes at any given moment.
Start with the dial or setting at the lowest position. Tow the trailer slowly in an empty parking lot and brake gently. If the trailer does not slow down noticeably, increase the controller setting by one or two notches and test again. Keep testing until the trailer brakes feel balanced with your vehicle's brakes — the trailer should not pull to one side, and you should not feel a jerk or lurch.
If the trailer locks up (wheels stop rolling but the trailer skids), the controller is set too high. Turn it down one notch and test again. Most trailers work best with the controller set between the middle and three-quarters of the way up the dial, but this varies by trailer weight and brake condition.
Accessing the brake assemblies on each wheel
Park the trailer on level ground and engage the parking brake. Use a jack to lift one wheel at a time, placing jack stands under the frame — never work under a trailer supported only by a jack. Remove the wheel to expose the brake drum.
The brake assembly sits behind the drum. You will see a backing plate (a flat metal disc) with the brake shoes and other components attached. Some trailers have a rubber dust cover over the adjustment mechanism; peel this back gently to access the star wheel or adjustment bolt underneath.
Before you adjust anything, spin the drum by hand. It should turn freely with only slight resistance. If it is hard to turn or makes grinding sounds, the shoes are too close and dragging. If it spins freely with no resistance at all, the shoes may be too far away.
Adjusting brake shoe clearance
Most electric brake assemblies use a star wheel adjuster — a small gear-like wheel visible through a slot in the backing plate. Turning this wheel moves the brake shoes closer to or farther from the drum. You will need a brake spoon (a long-handled tool with a notch on each end) or a flat screwdriver to rotate it.
Insert the tool into the slot and hook it under the star wheel. Rotate the wheel toward the front of the trailer (upward if you are looking at the backing plate from behind the wheel). This pushes the shoes outward toward the drum. Turn it slowly and spin the drum after every few clicks. Stop when the drum becomes hard to turn — the shoes are now close to the drum.
Back off the star wheel by rotating it the opposite direction (downward) until the drum spins freely again with only light drag. This gap of 0.010 to 0.015 inches is your target. The drum should turn without resistance but should not spin freely as if the brakes were not there at all.
Some trailers use a bolt adjuster instead of a star wheel. This is a single bolt on the backing plate that you turn with a wrench. Turn it clockwise to tighten (move shoes closer) and counterclockwise to loosen. The same principle applies: tighten until the drum drags, then back off until it spins freely with light resistance.
Testing your adjustments before towing
After adjusting all four wheels, lower the trailer and spin each wheel by hand one more time. All four should feel similar — if one is noticeably harder to turn than the others, adjust that one again. Uneven resistance means uneven braking, which will pull the trailer to one side when you brake.
Tow the trailer in an empty parking lot at low speed and brake gently. The trailer should slow smoothly without pulling left or right. Brake harder to feel how the trailer responds. If it locks up, the controller is too high or one brake assembly is adjusted too tight — lower the controller setting first, then test again.
Drive for a few minutes, then stop and feel the brake drums on each wheel. They should all be warm but not hot enough to hurt your hand. If one drum is much hotter than the others, that brake is dragging and needs to be backed off.
When to stop and get help
If the trailer pulls sharply to one side when braking, stop when ready and do not tow until you have checked all four brakes. This usually means one brake is not working or one is adjusted too tight. Uneven braking can cause jackknifing on the highway.
If you smell burning rubber or hot metal while towing, pull over safely and let the brakes cool. Feel each drum carefully — do not touch it directly. If one is much hotter than the others, that brake is dragging badly. Lower the controller setting and back off that brake's adjustment, then test again in the parking lot before returning to the road.
If the trailer brakes do not respond at all even with the controller turned all the way up, the problem is likely electrical rather than mechanical. Check that the trailer connector is clean and fully seated, and that the tow vehicle's battery is fully charged. If the brakes still do not work, the brake controller or wiring may need replacement.
Frequently Asked Questions
How often should I adjust electric brakes?
Brake shoes wear over time, so you may need to adjust the star wheel or bolt every 10,000 to 15,000 miles of towing. Check the drum resistance every time you tow — if it spins too freely, tighten the adjuster. If you tow frequently or in hilly terrain, check more often.
What if I cannot find the star wheel or adjuster on my brake assembly?
Some brake models have the adjuster on the inside of the backing plate, facing the drum. You may need to remove the drum completely to access it. Check your trailer manual for the exact location and procedure for your brake model before you start.
Can I adjust the brakes while the trailer is parked on a slope?
No. Always park on level ground and use jack stands. A slope will throw off your adjustment because gravity will affect how the shoes sit against the drum. Level ground gives you an accurate baseline.
What does it mean if one brake locks up before the others during braking?
That brake is adjusted too tight or the controller setting is too high. Back off that brake's adjuster first, then test. If it still locks up, lower the controller setting. Locking happens when one brake engages before the others can, which causes the wheel to stop rolling while the trailer is still moving.
Is it normal for the brake drums to get warm while towing?
Yes, they should feel warm to the touch after braking. If they are too hot to hold your hand on for more than a few seconds, the brakes are dragging. Stop, let them cool, and back off the adjustment on the hottest drum.