Single Brake Magnet Failure And Diagnosis

On our last trip we had some annoying low-speed brake squealing. Backing off on the brake controller helped a little. But it was already set fairly low. I waited till we got home to do a modest shoe adjustment. I did, but to no avail.

I pulled the hub apart (first time) and was thrust into a new world of discovery and learning. Everything looked fine, to my untrained eye, so I carefully put it back together after cleaning out a bit of rust and dust on the drum. No change.

Out of curiosity I jacked up each side of the trailer separately, manually spun each tire, and manually activated the TV brake controller: one side worked; the other didn't. A voltage test at the wires of the non-functioning brake revealed that it was getting power. So... I had a bad brake. But what to do? I had never seen, much less tried to fix one of these.

E-trailer to the rescue: https://www.etrailer.com/faq-testing-trailer-brake-magnets-for-proper-function.aspx

I removed the brake assembly and tested it with a spare 12V battery. The magnet was drawing 18 amps when connected to the stand-alone battery, when it should only have been drawing 3.0 to 3.2A. I ordered a new Dexter 7" full brake assembly as the magnet part alone would have been nearly half that cost of a full replacement. I'll be putting it all back together under the supervision of my auto mechanic in the next couple days.

A couple things I learned in the process that may be new to some, and old hat to others:

1) Don't mix greases when re-packing as they may be incompatible. Fully remove all the grease so you can carefully inspect the bearings and races to determine if they are suitable for reuse. (In my case, they were.)
2) Don't mix new bearings with old races as they haven't seated and worn in together.
3) Always use a new seal and cotter pin/tang washer for reassembly. They are cheap.
4) Not all bearing kits for 1 1/16" axles come with all the correct parts. The spare emergency SKF kit I had been carrying all this time had the correct bearings and races, but the wrong grease seal. Correct part numbers are listed on the C-I parts page.
5) Magnet electrical failure is one of the more common brake issues, and is easily diagnosed with a multimeter. So they are a good place to start looking if you have a brake issue and have the hub all apart.
6) Road-testing the trailer's brakes using the manual lever on the brake controller (putting the TV into neutral at speed) will tell you if there is some, or adequate, trailer braking, but it won't tell you if there is an independent and isolated failure on just one side. Jacking each side like I did and giving them each a spin will tell you if you are dealing with a bilateral issue, or not. This will narrow down list of potential causes very quickly.

It remains to be seen if doing this one side will fix my brake squeal. I somehow doubt it, and that I will be pulling the other side apart as well.

 

Good tips. Make sure to use correct grease and dont pack the hub.

 

Thanks Kevin. My mechanic packed them for me as they have a press. Neater and less fuss.

Brake installation complete, and no more squealing.

I used the "20X Slow-down from 40 mph to 20 mph" burnishing procedure: "The Proper Way to Burnish your Trailer Brakes" | www.OrderTrailerParts.com as their quick-and-dirty high-speed red-hot "pro tech" method scared me just a little. And I was in no hurry.

Both sides were re-adjusted a couple notches outward afterward as the burnishing did take something off them. Be careful as all components do get hot, even using the 20X method. I then tested each with a manual spin at a low controller setting, and both wheels off the ground. Just to make sure that both sides were grabbing equally.

Prior to hub assembly, I checked the magnet's amp draw at full power and got a reading of 2.8A with the clamp meter around one of the brakes wires. Which is where it should be with a 7" Dexter, and slightly less than other brake manufacturer's 3.0-3.2A specs, and felt safe putting it all back together.

When the left brake goes bad or wears out, I now should be able to diagnose and/or replace it in a lot less time. Providing I remember what I just did.