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  1. #1
    King Pin
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    Quick and Easy Brake Magnet Check

    I know many of you old timers know this trick. But here's a simple tool to make sure your brake magnets are working.

    When you apply the electric trailer brakes, it actuates a magnet which rubs on the hub and causes the brake shoes to expand and apply braking force. You can use a magnetic compass to verify that the magnets are actuating when you apply the brakes.


    Step one - set a compass near the bottom of your wheel between the spokes so it's close to the brake drum and note the direction of the compass needle.


    Step two - Pull the break away pin.


    Step three - Verify that the needle on the compass deflects.

    Step four - Replace the break-away pin.

    Step five - Repeat for each wheel.

    If so, your brake magnets are engaging. If there is no deflection on the compass needle, you need to do deeper trouble-shooting.

    Note 1: The needle may not point directly towards the magnet because it's a broad magnetic field that is set up. You're simply looking for needle changes between when the brakes are applied and when they're not.

    Note 2: You may want to have someone assist with the test by applying the brakes from the tow vehicle while you check the compass needle. This will verify that your tow vehicle brake wiring and controller are functioning.

    Jim
    Last edited by TucsonJim; 03-31-2018 at 10:41 AM.

  2. #2
    Big Traveler
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    Thank you for posting this! I'm going to definitely check my trailer when I pick it up in 10 days.
    2017 Ford F450 - our kids call her "Big Red"
    2018 Grand Design Reflection 28bh

  3. #3
    Big Traveler Grandesigner's Avatar
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    I have used the audio method by listening for the hum while someone activates the brakes, but I may try this visual method also...
    Dan and Rita
    2021 Reflection150 260RD, built June 2020, w/400W solar + 2 size 31 AGMs, added 2" lift blocks to match the
    2022 F350 SCSB 7.3 GdZa 4x4, 10 Sp w/4.30s - Lariat Sport in Atlas Blue

  4. #4
    Site Team xrated's Avatar
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    Just keep in mind when doing this, the method described above will in fact tell you whether or not the magnet is working, but it will tell you NOTHING about if the brakes are adjusted properly or not.
    2016 F350 CrewCab Dually
    2018 Momentum 394M...Heavily Modded!
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    Excessive Payload is a Wonderful Thing

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  5. #5
    Big Traveler Grandesigner's Avatar
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    Yes, but adjustment happens in cab for the most part. Proper adjustment is the tricky part...
    Dan and Rita
    2021 Reflection150 260RD, built June 2020, w/400W solar + 2 size 31 AGMs, added 2" lift blocks to match the
    2022 F350 SCSB 7.3 GdZa 4x4, 10 Sp w/4.30s - Lariat Sport in Atlas Blue

  6. #6
    Site Sponsor
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    Quote Originally Posted by Grandesigner View Post
    Yes, but adjustment happens in cab for the most part. Proper adjustment is the tricky part...
    Adjustment is done by crawling under the trailer and adjusting the shoes on most trailers, and even on those with self-adjusting brakes you need to check that the adjusters are doing their jobs.
    John & Kathy
    2014 F250 Lariat FX4 6.2L SBCC
    2014 Reflection 303RLS
    SW Indiana

  7. #7
    Big Traveler Grandesigner's Avatar
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    Yeah, forgot about those...my last 3 trailers have had working self adjusters...
    I had to adjust the brakes on my 69 Mach1, kind of surprised that old tech is still being sold.
    Dan and Rita
    2021 Reflection150 260RD, built June 2020, w/400W solar + 2 size 31 AGMs, added 2" lift blocks to match the
    2022 F350 SCSB 7.3 GdZa 4x4, 10 Sp w/4.30s - Lariat Sport in Atlas Blue

  8. #8
    Site Team WhittleBurner's Avatar
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    There is a tool for setting the brake adjustment correctly first time every time. It's called a GEARWRENCH break resetting gauge now. In the old days when cars had 4 wheel drum it was called a safety set. With 4 wheel drum trying to get all 4 wheels set exactly the same so there would be no pull took a special knack. With this tool you fit one side to the inside of the drum. Then you slip the other side over the shoes and you will have the proper adjustment and all wheels will be the same. Do it on each wheel as the drums wouldn't have the same measurements. It does work quite well.
    Marcy & Gary
    2014 Grand Design - Reflection 303RLS
    2022 GMC 3500 Denali Duramax Longbed SRW
    2015 GMC Denali 3500 - Retired
    2003 F350 - retired
    Michigan
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