What Ohms Should Trailer Brake Magnets Be?

Question

Question:

When I have my brake controller connected and I apply my brakes, the trailer brakes grab regardless of the gain setting. I checked the ground and its good. I checked the resistance at each brake and one reads 2.0 ohms and the other reads 2.8 ohms. Single axle.

asked by: Patrick F

0

Expert Reply:

Assuming that when you tested the resistance of the brakes you were testing the two wires on each magnet and getting 2.0 and 2.8 ohms the magnets on your trailer are not working correctly and will need to be replaced.

For 7" brakes you should get 3.8-4.0 ohms, and for 10-12" brakes you should have 3.0-3.8 ohms.

If the brake shoes themselves are good you can replace just the magnet using 7" # AKBRKR-M7, 10" # AKBRKR-M10, or 12" # AKBRKR-M12.

If the shoes are needing replacement as well you will need to go with 7" braking assembly # AKEBRK-2, 10" # AKEBRK-35-SA, or 12" # AKEBRK-7-SA.

I included videos for the products mentioned for you to take a look at.

expert reply by: Samuel C

0

Mike

7/6/2024

I tested resistance at the 7 pin connector: between brake terminal and ground. I got 1.7ohms which I think means it would pull about 7 amps (between the 2 brakes) if I understand correctly. Sound right? Thanks.

Samuel C.

7/6/2024

@Mike You're going to need to test at the magnet, as testing at the 7-way adds in a lot of additional wiring leading to weird results. You should have more resistance than 1.7ohms, that is almost half of normal readings, though you may be getting a weird reading based on where you're testing (at the 7-way and not directly to the magnet)

Johnc. B.

3/16/2025

@SamuelC

Kate F.

3/17/2025

@JohncB Hey there John, did you have a question? I don't see that one was written...

Jason Y.

1/15/2025

Hey Sam, My rear wheel drum on my Coromal Element tandem caravan is heating up after a short trip. The other 3 drums are fine. I have checked the ohms and they are all between 3.1-3.3. I have adjusted the shoes, checked the bearings. I am lost now?????? Do you have another suggestion as to what could be the problem mate Please

Kate F.

1/15/2025

@JasonY Hello Jason. I am sorry to hear that one of your drums is heating up. Since you already checked your bearings and adjusted your shoes, it could be a sticking magnet. You will want to jack the trailer up and manually spin the wheel while someone else activates the brake controller to ensure it releases fully when power is off. If that turns out ok, I would check the magnet for glazing/contamination. If it is glazed it will look smooth and polished instead of that rough matte surface, if you are unsure I would compare it to one of the ones that is working correctly. Also inspect the drum, if it is glazed over it will cause uneven wear or grooved patterns from excessive contact with the drum. If it is slightly glazed you could use some 120-150 grit sandpaper to LIGHTLY sand the magnet, if it is too worn you will need to replace the brake shoe, or at least the magnet. One last thing to look over is the brake wire that there isn't any damage and the connection is good. Let me know how things turn out. Feel free to send me pictures of the drum and brake shoe if you need a second set of eyes. I know you thought you were asking Sam the question, he is now in charge of our training classes so he can spread his great knowledge with the rest of the etrailer employees, and he is doing a Fantastic job at it too!

Jason

1/16/2025

@KateF Thanks so much for your reply. I checked the ohms on all 4 magnets and they all sit at 3.2. I will check the magnet as you said and see if I can notice anything you mentioned. Thank you

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What Ohms Should Trailer Brake Magnets Be?

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