Troubleshooting Electric Trailer Brakes That Hum But Do Not Engage Drums
Updated 08/04/2025 | Published 06/09/2017
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Question:
I am trying to get my trailer brakes to work. I can hear a humming sound on the trailer brakes but they arent applying. I dont know what to do cause Ive never worked on electric trailer brakes
asked by: Brady
Expert Reply:
The humming sound you hear from your trailer's electric drum brakes is a good sign. It means that the brakes' magnets are being energized by the output from the trailer brake controller in the vehicle. The issue with the brakes not applying pressure to the drums could simply be a matter of adjustment, or it could have another cause.
Drum brakes like # AKEBRK-35 have an adjustment device called a star wheel that is located near the bottom of the magnet. Please refer to the picture I prepared for you. Rotating the star wheel upward (as viewed from outside) increases the pressure the brake shows will apply to the drum surface. This wheel can be adjusted with a flat-blade screwdriver or with a brake spoon # W80630. There is a slot in the back of the main plate that allows you to insert the spoon tool.
When a drum brake is adjusted correctly there will be slight drag on the drum when you rotate it by hand. You should be able to hear and feel this drag. Try adjusting your brakes so that they drag slightly on the drum and then test the trailer with your vehicle.
The other possibility is that the brake shoes are worn and this is why there is inadequate pressure on the drums. You can compare the appearance of your brake shoes (specifically their pad thickness) to those on new brakes on our site to see if wear is the issue.
The other possibility is that your trailer brake controller is either set to too low a power level or that it is the proportional type that relies on trailer motion to tell it to generate an output signal. You can set the unit to maximum power and boost and then use the manual override lever to send this full-power signal to your trailer brakes. The brakes definitely should engage when they receive this full-power signal.
You can also refer to the linked articles for more guidance on trailer brakes.
Product Page this Question was Asked From
etrailer Electric Trailer Brakes - 10" - Left/Right Hand Assemblies - 3,500 lbs
- Trailer Brakes
- Electric Drum Brakes
- Standard Grade
- Manual Adjust
- 10 x 2-1/4 Inch Drum
- 3500 lbs Axle
- 14 Inch Wheel
- 14-1/2 Inch Wheel
- 15 Inch Wheel
- etrailer
more information >
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Ron M.
8/4/2025
Had a question as to why my trailer brakes hum when parked. You answered for another person .thanx.