Electric Trailer Brakes Are Weak Even with Trailer Unloaded
Question:
We have a trailer with brakes that are about two years old and very poor performance. I am not sure how many miles that would be but we use the trailer a lot and haul some pretty heavy loads. The brakes look fine, they are not rusted up, and I lubricated all the pivot/ contact points, but still just dont work the best. With the brake controller turned all the way up, and an empty trailer the tires wouldnt skid, even on a snow covered road. They are 12 1/4 x 3 3/8 inch brakes. What should the ohms be for those magnets? I dont have an ammeter, but will be getting one soon. What should the amps be? I tested one magnet and the ohms were 4.2. Is that too high? The brake shoes themselves have a lot of meat left on them. Would it be likely that the magnets would go bad that soon, and before the brake shoes are even wore down. The magnets appear to be in good shape, and the surface of the drum where they ride is fairly smooth.
asked by: Mark R
Expert Reply:
There are some common things you can check to determine what is causing the poor braking performance. First, you do not want the trailer brakes to lock up and skid. You want them to be at a point just under that.
The resistance of 12-1/4 inch by 3-3/8 inch brakes should be 3.2 Ohms. The amperage draw per magnet should be 3.0 amps. If you look at the magnets and can see the copper windings coming through then the magnets will need to be replaced.
If you have Dexter 12-1/4 x 3-3/8 Stamped Backing Plate or Dexter 12-1/4 x 3-3/8 Cast Backing Plate then you can use replacement magnet # BP01-301.
You will also want to check the brake magnet power and ground wires. You will be looking for any frayed wires that might be causing a short. For the grounds, make sure they are attached to clean and corrosion free bare metal surfaces near the magnets. You will also want to make sure the brakes are properly adjusted. Basically you will adjust the brakes until you can hear a slight but constant drag on the drum.
You will also want to check the trailer and vehicle side connectors. Make sure they are clean and free of corrosion inside and out. On the vehicle side, there could also be something wrong with the output wiring from the brake controller or the controller itself. You can trace the brake output wire from the connector (7 oclock position if looking at back of plug on vehicle) forward. Look for frayed wires again and fix as needed.
To test the controller you can use a multimeter such as # PT89ZR. You will need to sever the blue wire several inches from the back of the controller. Then test the end coming out of the controller. With the power set to the maximum it should be putting out at least 12 volts when you apply the manual override. It should not show power at any other time.
If it is under 12 volts or shows power all the time then there is something wrong inside the controller and it will need to be replaced. You will also need to make sure the controller is mounted according to the instructions and not tilted or turned to one side or the other. This can affect performance.
I have included some links that should help you. Typically when troubleshooting braking issues you would start with the brake controller but you can look at the trailer brakes themselves first if you want.
Products Referenced in This Question
Digital Multimeter with 42" Long Test Leads - LED Display
- Electrical Tools
- Testers
- Multimeter
- Yellow
- Performance Tool
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