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Old 05-25-2017, 05:30 PM   #1
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Brake magnet drag

I'm wondering if it's normal for the brake magnets to drag a little bit. Both sides seem to have a light constant dragging sound and I'm sure it's not the pads. I actually loosened them up a bit to see if the noise went away, which it didn't. The drums seem to spin fairly well though one side is a bit louder than the other.

Everything looked good when I re-packed the bearings, but since this is my first experience with the electric brakes I'm not sure what is considered normal or not for the magnets. I had it out on the road for a bit today and used my IR gun to check the top of the brake drums - the side where the noise is louder was about 15-20 degrees hotter - around 155-160 after about 20 miles freeway and a few miles side roads.

I looked through the Dexter manual but most of the magnet troubleshooting is electrical and didn't see anything that mentioned dragging or constant friction on the magnet, only dragging shoes.
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Old 05-25-2017, 08:58 PM   #2
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This may help a bit, found it on etrailer web site.

The magnet should only make contact with the inside of the brake drum when power is applied to the magnet. If it is making contact with the drum all the time, you may have residual power running on the brake wire that is just enough to cause the magnet to grab the drum.

You will need to check the magnet power wire with a circuit tester, # 3808, to see if there is any power when the brakes are not applied. If there is, there is a short circuit somewhere and you will need to track it down. Look for loose or broken connections and wires with nicks in them. Also check to make sure the ground wires are attached to a clean metal surface both from the magnets and on the trailer and vehicle side connectors.

Also check for any dirt or corrosion on the inside and outside of the trailer connectors on both the vehicle and trailer side connectors.

You will also want to pull the hub and check for any grooves cut into the drum and wear on the magnet. If the magnet is worn it will need to be replaced. If you see or feel grooves on the inside of the drum it will need to be replaced. I have included an FAQ article that might help with further testing the magnet.
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Old 05-25-2017, 10:10 PM   #3
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Thanks for the info Sundancer330 - after reading through that info and thinking back two or three weeks to when I did the bearings the residual power may have something to do with it. When I did the bearings I don't recall hearing the constant dragging sound after putting things back together. For that work I had the trailer hitched to the truck but didn't have the umbilical attached. Today I had it out on the road and when I lifted it up to check the drums the umbilical was connected. I think I'll start by lifting it up and spinning the wheels again without the umbilical connected and see if the noise is gone or diminished, then plug the umbilical in and see if it comes back. If so then perhaps there is something up with the factory brake controller in the RAM. I do know that the 7-pin on the RAM does provide power even with the engine off and key removed. If not, the weather is supposed to be great here for the long w/e so I'll dig into it further.. (I'm on-call this week-end so no camping for me.. )
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Old 05-27-2017, 01:02 PM   #4
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I got into this yesterday afternoon and started by checking the base voltage at the 7-pin connector on the truck. With the key off there was no measurable voltage on the brake pin and the expected 12.7+ volts on the charge pin as the RAM provides that even with the key out. With the engine running the brake pin showed a steady 1 volt.

Next I check the voltage at the brake connections just outside the hub and got the same results so it would seem that electrically things are OK. I then had the DW use the manual slider on the brake controller while I spun the drum. I could hear the magnet energize and the brakes engaged. However, on one side I could tell that once the magnet was de-energized the brakes didn't fully release. When I had them apart a couple of weeks ago things seemed to be fairly clean and in working order.

So I pulled the drums again and removed all the brake components. While they looked pretty decent front side I found that where the shoes and the magnet arm contact the back plate there was a build-up that would seem to catch from time to time. Also, the bushing at the top of the magnet arm was rather stiff as well. I cleaned the back plate and all contact points with brake cleaner and a wire brush, then applied some brake component grease and re-assembled. When I put the tires on I left off the chrome trim cover that was over the hub so I can get more accurate hub temp readings.

After re-assembly there is still a slight dragging sound but much fainter than before. I believe that is the spring behind the magnet that is keeping the magnet up against the drum with just a little pressure.

This morning I took it out for a road trip - about 50-60 miles mostly freeway. I made a stop about 10 miles in for an initial hub and drum temp reading and the results were much better - hubs were within a couple degrees of each other around 110 and the top of the drums the same at about 125 each. After running the remaining 40-50 miles the hubs were holding around 112-114 each and the drums around 135 each. The brakes seemed to work better and the slight squeal I heard the other day was also gone.

So I think I'm ready to hit the road now - first trip coming up in June... :-)
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Old 05-28-2017, 11:38 PM   #5
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Im wondering about the steady 1 volt your seeing at the brake pin! seems it should be zero untill you apply the brakes
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Old 05-29-2017, 09:02 AM   #6
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I did some additional research on this and still not certain on what the expectation is for the RAM factory controller. In some Dexter documentation I found that they listed 2 volts as a "threshold voltage" which I interpreted to mean the point at which the magnets would energize enough to start engaging. I made an assumption that the 1 volt was used by the controller to be able to determine whether or not brakes were detected.

I also found some posts on some RAM forums where folks were talking about factory brake controller issues. In that situation it sounded like the controller was putting out a steady 1.5 volts which they felt may have contributed to their problem of excessive and early brake wear. I don't see any odd or excessive wear on my brakes - they just seemed to be a bit sticky and not fully releasing when the magnet de-energized.

I'm going to call my dealer tomorrow and ask them about this as I need to schedule a fluid change in the rear differential anyway before we start the season. Even without any voltage applied I don't see how there would be no contact at all between the magnet and the drum given the force of the spring behind the magnet.
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