How do I know when the magnets in my electric trailer brakes are worn out?

My Dexter electric trailer brakes on my travel trailer are size 10%26quot; x 1 1/2%26quot;.

Electric current causes a magnet to contact the inside of the brake drum to engage a lever that pushes the brake shoes against the drum to slow down the trailer. Can the contact surfaces of both the magnet and the brake drum be machined flat to achieve a better contact area? How much of the metal surface of the magnet can be removed before it becomes useless?How do I know when the magnets in my electric trailer brakes are worn out?You don't ever machine the magnets. Occasionally the drums will need to be turned to remove grooving that occurs naturally from break wear. The magnets or more correctly the brake actuators are replaced as a set. There are however a few checks that you need to do first. First question is, Do you have Surge brakes or a truck mounted controller? If you have surge brakes there should be an LED on the top when you plug it in to your vehicle it should come on to tell you if the brakes are working or not. If you have a truck mounted brake controller, you should also have an indicator light on the front of the module. With the truck mounted controller you have the added option of a brake lever.(A spring loaded slide switch on the front of the unit and an adjustment wheel usually located on the side of the unit. Set the adjustment wheel to maximum setting after hooking the trailer up. Pull forward slowly and pull the slide lever to manually activate the brakes. If your trailer wheels lock and drag then the brakes are working properly. reset them back to there normal setting where you can just feel a little pull on the trailer when you engage the manual slider. The magnets as a rule almost never wear out. Usually the drums or the pads or the mechanical parts fail long before the magnets will ever fail to work. More than likely you have a broken wire or your controller has failed for some reason. Surge brakes are prone to controller failure and a truck mounted unit is easier to check for failure than a surge type. Personally I prefer the truck mounted unit as it is more adaptable to different loads and can be manually adjusted for heavier loads. As to the magnets, I have never had a failure and i have used and worked on hundreds of these types of brakes. You might have some corrosion around the solenoid where the piston moves in and out of the magnets which will stop it from working. My main advise is if you do not have experience with this type of brake system then take it to a professional. You need both mechanical and electrical experience to work on these systems beyond the basic checks I have described above.How do I know when the magnets in my electric trailer brakes are worn out?no more then 100 thous of an inchuse your desgression heres a link read page 10 http://dexteraxle.com/i/u/1080235/f/6-8KHow do I know when the magnets in my electric trailer brakes are worn out?cant be resurfaced. the only way to tell if bad, is to pull tire and drum and visually inspect alot can be ground off, most common problem is one of the wires breaks close enough to the magnet as it cant be spliced