Trailer Brake Magnets Hum But Brakes Do Not Work
Question:
We have 1997 International 4700 with air brakes and a electric box for the trailer, the trailer brakes dont work, we can here them, when the brake is applied, but they dont work.
asked by: Tina C
Expert Reply:
It sounds like you are using a brake controller for the electric brakes on the trailer. There are several things that you can check to determine where the problem is.
In the truck cab you will need to sever the blue brake output wire several inches from the back of the controller. Then use a circuit tester such as # PTW2992 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override (or brake pedal on some controllers). If it shows power at idle, then there is something wrong with the controller and it will need to be replaced.
If it tests fine then reconnect the blue wire. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.
You can test the brake output pin and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.
If the truck side checks out fine then it could be the wiring to the brake magnets or the magnets themselves. Make sure the brakes are properly adjusted (there should be a slight but constant drag of the pads on the drums when the wheel is turned). Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.
You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.
Products Referenced in This Question
Product Page this Question was Asked From
Hydrastar Electric Over Hydraulic Actuator for Drum Brakes - 1,000 psi
- Brake Actuator
- Electric-Hydraulic Brake Actuator
- 1000 psi
- Drum Brakes
- Hydrastar
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