One Elec Brake not Equal to Other Three

[wingfoot321]

The left front brake does not have the same braking force as the other three.

I jacked the left side and was adjusting the brakes with the pigtail hooked to the truck. At a low amp setting on the controller ( 4-5 amps), I could turn the wheel slightly by hand with my wife pushing the brake pedal. I had to turn the controller up to 8-9 amps to clearly lock the front left brake. This was not true of the other three wheel positions.

Background: I just put a new drum on the left front. The magnet has a high spot on the lower edge. It had worn a groove into the old hub surface where the magnet touches.
Question 1, would a small gap between the magnet surface and the hub surface due to this high spot on the lower edge of the magnet cause a drop off in the force this brake could exert.
Question 2, is there a way to test the magnet without taking it off the trailer. My manual says to take it off and test with an ammeter and battery.

Your comments appreciated

[nickcrowhurst]

Wingfoot, re. question 1, without getting into the math of the situation, I would just say "yes". If I had to deal with this, I would prefer to replace all four brake assemblies, complete with new magnets, brake linings, springs, etc. I have spent far too much time and money attempting to replace parts of these brake systems. The whole backplates are surprisingly inexpensive, especially when compared to buying individual parts. If I had to economise, or just needed to get the trailer home, I would remove the magnet, and rub it on a piece of coarse emery paper resting on a thick flat piece of glass or steel until the ridge had gone. Then I would use some finer paper to smooth it off. There is obviously a limit to how much can be removed. The securing bolt heads should not be touched. That should be sufficient to pull the trailer safely to get you home. If you pull the trailer with the distorted magnet, you could ruin your new drum. Re. question 2, if you disconnect one wire nut behind the wheel and insert the ammeter between the two ends, you can compare the amperage with the factory spec. for the magnet when the brakes are applied. Good luck. Nick.