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  1. #1
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    Default Faulty electric brakes

    So I'm doing a bit of work to a horse float to get it through a RWC. Fitted new safety chains, replaced clearance lights, removed the guards and refitted them so there's enough clearance to the tyres and they actually stick out just past the wheels now instead of being about 30mm shy. I pulled the drums off ( x4 ) and cleaned out the 30 year old grease and repacked the bearings and put in new seals. I found that one magnet (electric brakes) had a broken wire so I robbed one off some other brakes I have for another project. Adjusted all the shoes and freed up all the pivots etc.

    I hooked up the tow vehicle and applied the brakes. I can hear all the magnets humming, but only one wheel is being braked, the others still spin freely. The controller is showing 3v going to the brakes and it works fine with my other trailers. Everything on the backing plate is operating freely so my guess is that the magnets are no longer strong enough to apply the brakes. I've never really played with them before but I assume they shouldn't be able to spin freely if the magnet is even pulling itself onto the drum. Any help appreciated,

    Mick
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  3. #2
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    I haven't had a lot to do with them, but my understanding is that the coil and core draw up against the machined "disk" surface on the drum wall, and the wheel rotation tries to rotate the core around the axle, and via linkages expands the drum shoes into the drum periphery.

    If this is the case, they don't cause the drum shoes to grab on the drum if there is not a moderate rotational speed on the wheel. For this reason they incorporate a mechanical handbreak to hold the drum shoes in the expanded position when parked.

    I would give it a slow lightly loaded tow to test them, rather than jacking and manually spinning them, or alternatively enquire of the tester you will use how they test them.

  4. #3
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    Interesting to see what the final outcome is.

    If it was mine I would check for good electrical connections to the suspect brakes.

    Dunno if a buildup of crud/rust between magnet and drum would be sufficient to give you issues.
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  5. #4
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    I checked all the connections and redid some of them, all good now. I can see how the brakes work, and I'm fairly certain that it doesn't matter what speed the drum is spinning, the magnet should still stick to the flat surface on the inside and then be moved around, with the attached lever forcing the shoes apart thereby providing braking. One drum will do this, it takes about an 1/8th of a turn and the brakes are applied. I have read on a distributors website that the magnets do get weak causing poor/no braking. I was hoping someone could confirm this before I order 4 magnets.

    Mick
    "If you need a machine today and don't buy it,

    tomorrow you will have paid for it and not have it."

    - Henry Ford 1938

  6. #5
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    You are correct in your assumption that the brakes work no matter what speed.

    In all my experience with Electric Brakes, this is the first time I've heard of magnets getting weak. They are not a magnet as such, and therefore are not something that loses their magnetism. They have an internal winding of copper wire that creates an electromagnetic field when powered. The greater the voltage supplied by the controller, the stronger the magnetic field becomes, and the harder the "magnet" tries to grab the drum, pulling the brakes on. If you have differing voltage to each of the magnets, then you will get differing brake performance from each of the brakes. You need a minimum of 4mm cable for both power and earth. And if you want to get pedantic, the same length cable from each magnet to the centre of the axle so there's no voltage drop from one side to the other. Adjustment is also critical for even braking performance. Four-wheeled electric brakes are even more of a PITA to get right than two-wheeled ones.
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  7. #6
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    Thanks for the reply Yonnee, All the wiring is good, I replaced the main feed a while back with twin 6mm. Checked the individual feeds the other day and redid some of the connections. Now that you mention it, being electro-magnets they're not going to lose their power gradually. They'll either work properly or not at all. I was just going off what a retailer had on their website.

    I'm going to back off the shoes a bit on the drum that was grabbing and then road test it. Before that though I'll grab someone to apply the brakes for me while I listen for the magnets to "click" against the inside of the drum. When I tested it the other day it was just by holding the pedal down with a prop. The other thing I read somewhere was to test the magnets by using a compass (navigation type) to see if the magnetic field makes the needle swing around.

    Mick
    "If you need a machine today and don't buy it,

    tomorrow you will have paid for it and not have it."

    - Henry Ford 1938

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