Electric trailer brakes need adjustment when stopping distance increases or brakes feel soft

Electric trailer brakes work through a brake controller mounted in your tow vehicle that sends power to electromagnets on each wheel. Over time, brake shoes wear down and the air gap between the shoe and drum grows larger. When that gap exceeds the controller's ability to compensate, you lose braking power. Adjustment means closing that gap by turning the adjuster bolt on each brake assembly until the shoe sits closer to the drum again.

The adjustment itself is straightforward: you access the adjuster through a hole in the brake drum backing plate, turn a star wheel or bolt until you feel resistance, then back off slightly. The whole process takes 30 to 45 minutes per axle if you have the right tools and know what you're feeling for. Most trailers have two or four brake assemblies depending on axle count.

Key Takeaways

  • Electric brakes adjust through a star wheel or bolt accessed via a hole in the backing plate; you turn it until the shoe contacts the drum, then back off a quarter turn.
  • You need a brake spoon (a long-handled tool with a notched end) or a standard screwdriver to turn the adjuster; a socket wrench works if you have the right size.
  • Spin the wheel by hand after each adjustment to confirm the brake shoe does not drag; dragging shoes overheat and wear unevenly.
  • Both sides of an axle must be adjusted equally, or the trailer will pull to one side during braking.
  • If adjustment does not restore braking power, the shoes may be worn below minimum thickness and need replacement rather than adjustment.

Locate the adjuster hole and identify your brake type

The adjuster hole sits on the back of the brake drum, usually on the bottom half of the backing plate. It is a small round opening, sometimes covered with a rubber plug or metal cap. Remove the plug or cap by hand or with a flat screwdriver. Behind it you will see either a star wheel (a small gear-like wheel with notches) or a slotted bolt, depending on your brake model.

Star wheels are most common on newer trailers and are easier to turn because the notches catch your tool. Slotted bolts require a screwdriver or wrench and offer less feedback as you turn. Both do the same job: moving the brake shoe closer to or farther from the drum. If you cannot find the hole, check your trailer's brake documentation or look at the opposite side of the same axle — the hole should be in the same position on both wheels.

Prepare the trailer and find the wheel

Park the trailer on level ground and engage the parking brake. Chock the wheels with blocks or wedges so the trailer cannot roll. You will be spinning the wheels by hand during adjustment, so stability matters. If you have a helper, have them sit in the tow vehicle with the engine off and foot off the brake pedal — this keeps the brake controller unpowered so the brakes do not engage unexpectedly while you work.

You do not need to remove the wheel to adjust the brakes, but some people do because it makes spinning the wheel easier and gives you better access to the adjuster hole. If you leave the wheel on, you can still spin it by hand by gripping the tire and turning it. If you remove the wheel, support the trailer on jack stands rated for your trailer's weight — never work under a trailer supported only by a jack.

Turn the adjuster until you feel resistance

Insert the brake spoon or screwdriver into the adjuster hole. For a star wheel, hook the notch with the spoon's end and turn upward (toward the top of the trailer). For a slotted bolt, turn clockwise. Turn slowly and feel for the point where the brake shoe contacts the drum — you will feel resistance increase as the shoe moves closer. Stop as soon as you feel solid resistance, not before.

This resistance point means the shoe is now touching the drum all the way around. Do not force it past this point; forcing damages the adjuster. Once you reach resistance, back off by turning the adjuster in the opposite direction. Back off one-quarter turn (for a star wheel, that is one notch; for a bolt, that is about 90 degrees). This small gap prevents the shoe from dragging and overheating during normal driving.

Spin the wheel and confirm the brake does not drag

Rotate the wheel by hand in the direction the trailer normally rolls. It should spin freely with no grinding, scraping, or heavy resistance. If it spins freely, the adjustment is correct. If you hear or feel dragging, the shoe is still too close to the drum. Back off the adjuster another quarter turn and spin again. Repeat until the wheel spins freely.

Dragging brakes overheat quickly and wear the shoe unevenly, which makes future adjustments harder and shortens the life of the brake assembly. A small amount of resistance is normal — electric brakes have some magnetic drag even when not powered — but you should be able to spin the wheel by hand without significant effort. If the wheel is hard to turn even after backing off the adjuster several times, the brake shoe may be worn too thin and need replacement.

Adjust the opposite wheel on the same axle equally

Move to the other side of the axle and repeat the adjustment process. It is critical that both wheels on the same axle are adjusted the same amount. If one side is tighter than the other, the trailer will pull to the tighter side during braking. This pulling can make the trailer unstable, especially at highway speeds or in emergency stops.

Count the number of turns or notches you made on the first wheel and make the same number on the second wheel. Spin both wheels again to confirm they have the same resistance and spin freely. If your trailer has two axles, repeat the process on the second axle. Some trailers have surge brakes (hydraulic) on the rear axle and electric brakes on the front, so check your documentation to see which axles have electric brakes before you start.

Test the brakes on the road at low speed

Once all adjustments are complete, start the tow vehicle and test the brakes in a safe area — an empty parking lot or quiet road with no traffic. Accelerate to 10 to 15 miles per hour and explore the brakes gently. The trailer should stop smoothly without pulling to either side. Increase speed gradually and test again at 20, 30, and 40 miles per hour if safe to do so.

The brakes should feel firm and responsive, not soft or spongy. If they still feel weak after adjustment, the brake controller may need adjustment (a separate procedure that varies by controller model), or the brake shoes may be worn below the minimum thickness and need replacement. If the trailer pulls to one side, return to the adjustment holes and verify that both sides of the axle are equally tight.

When to replace brakes instead of adjusting

Brake shoes have a minimum thickness, usually around 1/8 inch. If the shoe is thinner than this, adjustment will not restore braking power because there is not enough friction material left. You can check shoe thickness by looking through the adjuster hole with a flashlight — the shoe should look like a curved band of material, not a thin sliver.

If shoes are worn thin, they must be replaced. This is a more involved job that requires removing the brake drum, unbolting the old shoe assembly, and installing a new one. Some people do this themselves; others take the trailer to a shop. Replacement costs vary widely depending on the brake type and whether you do the work yourself, but typically range from $150 to $400 per wheel for parts and labor combined. Adjusting brakes regularly — every 6 to 12 months or whenever you notice soft braking — extends shoe life and delays replacement.

Frequently Asked Questions

How often should I adjust electric trailer brakes?

Adjust brakes whenever you notice stopping distance increasing or the brake pedal feeling softer than usual. For most trailers, this happens every 6 to 12 months depending on how often you tow and how hard you brake. Check the brakes at the start of each towing season as part of routine maintenance.

Can I adjust the brakes while the trailer is hooked to the tow vehicle?

Yes, but it is safer to unhook first. If the trailer is hooked up, make sure the parking brake is set, chock the wheels, and have someone keep the tow vehicle in park with the engine off. Unhooking takes five minutes and eliminates the risk of the trailer rolling if the parking brake fails.

What if the brakes still feel weak after I adjust them?

Weak brakes after adjustment usually mean the shoes are worn too thin to grip the drum effectively. Check the shoe thickness through the adjuster hole with a flashlight. If the shoes look thin, they need replacement. If the shoes look thick enough, the brake controller may need adjustment or the controller itself may be failing — consult your controller's manual or a brake shop.

Do I need to adjust the brakes on both axles?

Only if both axles have electric brakes. Many trailers have electric brakes on the front axle and surge brakes on the rear. Check your trailer's documentation or look at the brake assemblies — electric brakes have a visible electromagnet coil; surge brakes do not. Adjust only the axles with electric brakes.

What is the difference between a brake spoon and a regular screwdriver?

A brake spoon has a long handle and a notched end designed to catch the star wheel without slipping. A screwdriver works but can slip off the notches, especially if you are tired or the notches are worn. A spoon costs $5 to $15 and makes the job faster and safer. If you do not have one, a screwdriver works in a pinch, but go slowly and be ready for it to slip.