Electric trailer brakes

Joined
Mar 21, 2004
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Upstate NY
So my 20 year old Road Boss trailer has electric brakes I assume on all 4 wheels. I have only worked on surge brakes for boat trailers.

I assume it has a magnet, brake shoe and drum. I see online they sell kits to replace all the guys for $200 or so. Times two axles. Now it's expensive.

What typically breaks with the electric brakes? The trailer has been used once or twice a year. I assume I can buy all the parts individually? Does the magnet ever break.

Maybe just all rusted up? Maybe they work and I cannot tell?

How to test? Just apply 12V to the brake wire of the trailer connector?
 
Joined
Sep 27, 2015
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Each magnet has two wires, power and ground, that come out through the top center of the backing plate. Look for these wires and that they are connected to the brake wire and a good ground. The polarity does not matter. Some four wheel trailers only have brakes on the front wheels. All the magnets should be wired in parallel. Each one draws about 4 amps at 12 volts, so the resistance should check at about 3 ohms.

The test is to hook up the rig completely and pull the manual brake lever while driving forward slowly. The brakes only work going forward, they will not stop the trailer from moving backward. With the controller turned all the way up you should be able to make all the braked wheels skid.
 
Joined
Jul 12, 2012
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I have a car trailer with electric brakes and I went in to Napa parts and ordered all the parts I needed to do a complete brake job . The parts guy said they have complete parts kits that are cheaper than the individual components. Look into that before purchasing individual parts.
 
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May 30, 2010
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Take it apart and inspect. With that low of a use, i'd be surprised if the magnet is bad. Also check the cord connections for corrosion.
 
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Jan 3, 2006
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The magnets themselves seldom go bad, but the magnet does have a friction pad that rides against the flat side of the drum. Energizing the magnet pulls it against the drum, and the friction between the drum and the magnet pulls on the lever that expands the shoes into the outside of the drum, so it has to be moving to test them effectively. There is an adjusting star, works just like the adjustment on automotive drum brakes. There's usually a plug in the backing plate you can pop out to get to the star.

I added electric brakes to my popup camper, and the brake assemblies aren't all that expensive.
 
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Feb 25, 2015
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When I did the the breaks on my 5 horse a few years back I found the main issues were bad grounds, the friction material completely delaminated from the shoes and worn down magnets.

My drums and surprisingly the seals and bearings were fine. But after much research I suggest getting complete backing plates at minimum. They came to about the same price as magnets and shoes but easier to install in the end.
 

Donald

Thread starter
Joined
Mar 21, 2004
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Upstate NY
When I did the the breaks on my 5 horse a few years back I found the main issues were bad grounds, the friction material completely delaminated from the shoes and worn down magnets.

My drums and surprisingly the seals and bearings were fine. But after much research I suggest getting complete backing plates at minimum. They came to about the same price as magnets and shoes but easier to install in the end.
How does a magnet wear?
 
Joined
Sep 27, 2015
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It will be a lot easier to understand if you take one of the drums off and inspect the parts.

As Dave Sherman said, when the brakes are engaged, the magnet attracts itself to the moving outer vertical flat surface of the drum and drags on it. The drag force is approximately proportional to the magnet voltage being supplied from the brake controller. The drag pulls the magnet in the direction of wheel rotation, creating force on the magnet arm. The bottom end of the arm is a cam which pushes the brake shoes apart into the main friction area of the drum.

Almost all of the braking effect comes from the shoes, using force amplified from the drag of the magnet. The direct friction of the magnet is negligible in terms of slowing the vehicle down, but it will result in wear on the outer surface of the magnet. The magnet and its wear surface are replaced as one piece.

While the brakes are not applied, the magnet should spring away from the drum thus there is no wear.
 
Joined
Feb 20, 2007
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I have found brake force to vary with these. My first 2 axle trailer had maybe 20% brake ability brand new until I redid all of the factory connections. then it was pretty stout and could lock the wheels with full brake force, 5k lbs over 2 axles. My current single axle trailer won’t lock up, but provides enough force to work with the truck with minimal extra pedal force.
 
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