electric brake magnets

I think your close about being not expensive, you should find all the info you need in the link

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Hi. Some of the more modern brake controlers such as the Prodogy have readouts.
My son has a prodogy and his showed "Short" when his magnet required replacing but that is the exception due to bad maintenance.
I have electric brakes on my caravan and I check the magnets when I check the wheel bearings.
I have found that two sets of magnets will outlast one set of brake shoes. As per my son's work trailer. He is a self employed carpenter and the trailer is used every day

The magnets have wear holes in them. When you can no longer see the wear holes, they need replacing.

Can vary between 10,000k and 50,000k depending on how you use the trailer brakes, how heavy it is, flat country, hilly country, etc, etc.

I have Alko electric brakes on my campomatic - uses the heavy duty offroad magnets (rectangular shape with rounded ends) - just bought a pair to carry as spares for remote area travel - will change when required if I'm stuck - otherwise I can supply to a brake service centre when travelling. They are around $110 each magnet ! The metal face of the magnet has four small holes about 3mm deep - when they have gone the magnet should be replaced, but as said above, the controller might indicate magnet shorting just before that. Should be an easy field job - just cut the old magnet's supply wire and solder in the new unit.
Shoes are best bought as change-overs I'm told - about $100 for the set of 4 change over shoes I think - the only thing is that the brake drum MAY need to be machined a little, so a brake specialist might be best.
I carry bearings, seals and magnets, but not shoes.

Hi Gronk

I found a foolproof way to know - one of my magnets turned over and locked the wheel at 80 km/h on the highway between Kununurra & Turkey Creek. The smoke told me I needed to fix something!!

Before I left home, the magnets had rounded by I guess a mm or so from the centre and I foolishly said "That will do one more trip." Wrong.

1 mm sounds a good rule of thumb, but probably better to replace the lot (both sides) especially if you have been off road a lot. If the drum has grooves developing then you can't machine them as there is not enough meat so may as well replace them too. There is an off road magnet available now to prevent it roiling over and locking up - that would be worth it.
As others have said, the cost is not all that great.
Max