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Friday, October 30, 2009

Shorted Magnet

I have a Jayco 37-foot travel trailer with dual axles. I had one of the brake magnets short out and burn. I do have experience doing brake jobs on cars and trucks and think I should change both magnets for that one axle. Could you provide the repair instructions for this job? I will be at this campground for eleven weeks and would like to repair this problem before I leave. The brakes have a 12-inch drum on a Dexter axle.
Ed, (Ruskin, FL)


Ed, you are correct in thinking it's a good idea to always maintain the same age of all the components at each end of the same axle. By all means replace both magnets, but before beginning any procedure outlined here, make sure the trailer is properly raised and blocked safely with the tires completely off the ground. Use jack stands; don't rely on the hydraulic jack you use to raise the trailer! 

Here's the procedure: Remove the drum by first removing the dust cover, cotter pin and spindle nut and washer. Carefully remove the outer wheel bearing and cover it so dust does not settle on the bearing. Pull the drum away from the remainder of the brake assembly (it may be easier in some instances to first remove the tire and wheel). While you are there look for worn shoe linings. Replace the shoes if the lining is 1/16” thick or less. Replace them also if they are saturated with grease or oil or are cracked, gouged or if the lining has become separated from the shoes. Inspect the magnet arm for any loose or worn parts. Check the shoe return springs, mounting springs, and adjuster spring for deformation. Manually move the actuating arm and check for any binding or rubbing. Replace the magnets. 

In some instances it will be necessary to have the armature plate resurfaced. The armature is the smooth plate connected to the inside portion of the drum. This is the surface the magnet attaches to when energized. Call your local service facility if any armature has developed a pattern of grooves due to worn or damaged magnets. Remember, keep all like components on the same axle, the same age. 

In addition, there are two areas of the brake drum itself that are subject to wear and require periodic inspection. These two areas are the drum surface where the brake shoes actually make contact during stopping and the aforementioned armature surface where the magnet contacts. The drum surface should be inspected for excessive wear or heavy scoring. If the wear marks are worn more than .020”, or the drum has worn out of round by more than .015”, then the drum surface should be turned. If scoring or other wear is greater than .090”, the drum must be replaced. To ensure proper contact between the armature face and the magnet face, the magnets should be replaced whenever the armature place is resurfaced. Hopefully it's only the magnets that you’ll need to replace. But be sure to take the time to inspect everything since you’re going to expose all the components anyway.

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