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  1. #1
    Platinum Member
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    Feb 2004
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    529
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    Chicago suburban
    Tractor
    Kubota 2710

    Default Trailer brake magnet question

    Horse trailer I bought used awhile ago, just getting around to hooking up brakes. Controller and breakaway battery both deliver voltage to wires under trailer, so I pulled one of the wheels. The magnet has voltage to it, but there's no magnetic field that I can detect. How strong should the field be? I'm thinking it has to be pretty strong or this mechanism isn't going to work. The brake actuator is free and the shoes seem to move fine. I also don't hear any clicking noise on the other wheels when I apply the voltage. I don't believe all 4 magnets could be bad at once. Is it possible I'm getting a good voltage level but not enough current? I installed a new ground and fixed the old one, so there's two good quality grounds on bare metal. All electric lights work properly. Thanks for any suggestions, brakeless in Chicago...
    Mark Leininger

  2. #2
    Member
    Join Date
    Jun 2007
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    46
    Tractor
    NH TT50A with rear remotes added

    Default Re: Trailer brake magnet question

    Did you try to pull the emergency cable for the brakes? This is how I test mine on my horse trailer. With my truck (2005 Ford) it varies the current to the brakes, and if the truck is just sitting there, I get very little current.

    Just a suggestion.

    Bondoļ½©
    Bondo©
    05 F550 PSD 4X4 crew DRW towing beast.
    AERC member (www.aerc.org if you don't know what that is)!
    NH TT50A with rear remotes
    Oliver 770
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    If you ever meet someone who knows it all, you just met a fool !!!

  3. #3
    Super Member
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    Aug 2004
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    5,089
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    North of Mtl,Que,Can (Ste Adele)
    Tractor
    MT180D

    Default Re: Trailer brake magnet question

    The brake magnets do draw a fair amount of current hence all connections need to be well made in order to carry the current.
    In many cases simple twistlock connectors are used and they tend to allow corrosion.
    I like soldered connections with hear shrink type sleeves, however crimped connectors with a heat shrink sleeves is also OK.

    That being said, go directly to the splices closest to the brake magnets, undo the splice and apply the battery power at that point.
    You will also want to check the grounding (one side of the brake magnet goes to ground) for good bonding.
    To get a good ground you need to have bare metal and generally a star washer between the lugs and the frame to assure good bonding.

    Since you note that all 4 magnets do not seem to acivate I do believe that in all probability bad or corroded grounds and splices are the problem.

    Another approach would be to run a seperate grounding wire rather than rely on the frame to do that job as the frame return ground approach will always be open to corrosive bad connections. (kinda hard to keep water away from frame grounds).

    Just taping a splice is not adaquate to seal out moisture. You need to use heat shrink sleeves that have hot glue inside that acts as the sealant.

    If you use an ohm meter to check the coils you are looking for a low resistance reading to confirm continuity, (probably in the 5 to 50 ohm range) or again DC voltage applied would make a screwdriver hard to pull away.

    Good luck.

    ps; I had to rewire my small house trailer recently due to similar brake problems.

  4. #4
    Platinum Member
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    Feb 2004
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    529
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    Chicago suburban
    Tractor
    Kubota 2710

    Default Re: Trailer brake magnet question

    Quote Originally Posted by bondo
    Did you try to pull the emergency cable for the brakes?
    Bondoļ½©
    I'm calling the emergency cable the breakaway switch. That's what I've been using to do most of the testing. I tried the brake controller itself, with the same results.
    thanks
    Mark Leininger

  5. #5
    Platinum Member
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    Feb 2004
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    529
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    Chicago suburban
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    Kubota 2710

    Default Re: Trailer brake magnet question

    [QUOTE=PILOON]I like soldered connections with hear shrink type sleeves, however crimped connectors with a heat shrink sleeves is also OK.
    [\QUOTE]
    All soldered

    [QUOTE]
    Since you note that all 4 magnets do not seem to acivate I do believe that in all probability bad or corroded grounds and splices are the problem.
    [\QUOTE]
    Next step is to run a 12ga wire directly from car battery to the magnet and try it that way.

    [QUOTE]
    If you use an ohm meter to check the coils you are looking for a low resistance reading to confirm continuity, (probably in the 5 to 50 ohm range) or again DC voltage applied would make a screwdriver hard to pull away.
    [\QUOTE]

    Doh, why didn't I think of that. One magnet being close to short might draw enough current to keep them all from working. The are rather old (~15 year), so who knows what condition they're in.

    I hate trailers, horses, and the people who love them.
    Mark Leininger

  6. #6
    Platinum Member
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    Feb 2004
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    529
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    Chicago suburban
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    Kubota 2710

    Default Re: Trailer brake magnet question

    Bet this will be easier to read, sorry about the bad quote.

    Quote Originally Posted by PILOON
    I like soldered connections with hear shrink type sleeves, however crimped connectors with a heat shrink sleeves is also OK.
    All soldered

    Since you note that all 4 magnets do not seem to acivate I do believe that in all probability bad or corroded grounds and splices are the problem.
    Next step is to run a 12ga wire directly from car battery to the magnet and try it that way.

    If you use an ohm meter to check the coils you are looking for a low resistance reading to confirm continuity, (probably in the 5 to 50 ohm range) or again DC voltage applied would make a screwdriver hard to pull away.
    Doh, why didn't I think of that. One magnet being close to short might draw enough current to keep them all from working. The are rather old (~15 year), so who knows what condition they're in.
    Mark Leininger

  7. #7
    Platinum Member
    Join Date
    Feb 2004
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    529
    Location
    Chicago suburban
    Tractor
    Kubota 2710

    Default Re: Trailer brake magnet question

    Quote Originally Posted by PILOON
    That being said, go directly to the splices closest to the brake magnets, undo the splice and apply the battery power at that point.

    If you use an ohm meter to check the coils you are looking for a low resistance reading to confirm continuity, (probably in the 5 to 50 ohm range) or again DC voltage applied would make a screwdriver hard to pull away.
    Here's the end of the story for anyone still listening. I used Piloon's suggestion and clipped the wires close to the wheel, applied power/ground directly from the battery and got nothing. Checked resistance, completely open. Checked all 4 magnets this way, all were open. A little surprising, but the trailer is a '93, or maybe all 4 brakes overheated and killed the magnets. Anyway, I bought new electric brake assemblies for all 4 wheels from etrailer.com. They have some nice online videos on replacing trailer components, all went well other than getting the rusted nuts off. Thanks for help.
    Mark Leininger

  8. #8
    Veteran Member Rara Avis's Avatar
    Join Date
    Oct 2006
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    2,038
    Location
    VT, ND & OH
    Tractor
    John Deere

    Default Re: Trailer brake magnet question

    Road salt can age trailers prematurely...

    In VT, we replace our trailer plugs every couple of years because of it...

  9. #9
    Member
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    Jan 2008
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    45
    Location
    Texas

    Default Re: Trailer brake magnet question

    One of my trailer brakes wasnt working but was getting voltage i sanded the magnet and the area on the drum where the magnet engages the drum works great now

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