New to us trailer. 12K Dexter axles. On two separate trucks, the trailer starts in with normal feel of braking, then obvious that it gives no more. Weeks ago I verified it did have current on all 4 magnets, but I don't recall the values. But after looking at book specs, even when I tested the brakes directly to a battery, I don't think I got to that mark. As well, I'm sort of questioning if the trucks can even deliver the rated current which would be 12-15A. I am also wondering if the brakes auto adjusters are not doing their thing. Any other obvious issues or diag to consider? trying not to have to start popping off wheels and such. Not exactly a party.
you have not adjusted them? That is first thing on a new to you trailer. Screw the auto adjusters. Jack up a wheel, run the spoon on it, spin it test it. Next wheel. Then you have a clue without getting out the impact wrench.
Yeah.....lol There were several things to address so didn't really know about this deal. I found my current spec of measured 2.25A per magnet. That is technically under spec so I may need to look more at that, but by feel alone, they act like they engage but run out of poopoo, or rather travel. I guess someone called a 'shop' on this and they indicated $4k in new drums, rotors, bearings, and magnets will get it working good......LOL......
Since you have 4 brakes.... measure between ground (white) and brake (blue) wires at 7 pin connector. 1.0 to 1.2 ohm is correct.
Ohms Law enters the chat. Science, yo.
Ha, I know you are sharp on electrical work. The good ol high-Z DMM can fool ya on the ohms test, but certainly worth doing. I don't have a Simpson. I had to do a major rewire on that trailer after realizing why it was probably sold. They bought a China cord/plug where the colors were crazy off. They match colors and pretty much nothing worked. I have a 1mA resolution clamp meter I use for this stuff. I connected trailer directly to a battery to remove any PWM error, and tested each magnet. All were the same. Wire loss or something. I will prob have to open one of the magnet pigtails and see what's happening.
I need a whole book of these things to send people. Impedance, back EMF, and and power factor top the list.
Don't forget 'Ol Ely....eLy the iCe man that is.
That's a whole lot of horse chatter about one tiny part of the electric brake system. The magnet. Oh look my magnet's good! Yay! That must mean the brakes are okay!
Magnets. How do they work?
Agree, but these are electromagnets where their friction coefficient is relative to how much power they are puffing, thus the amount of lever force being applied to the shoes. However, I totally agree with you that first serve should be those adjusters.
Whatever you do, don't put them in water!!
I recently was having similar odd issues with my 15K equipment trailer, sometimes the brakes worked well, sometimes only seemed to be getting partial voltage, sometimes not at all. Shoes were getting a little thin so I installed all new OEM Dexter backing plates/brake components, problem didn't change. Turns out it was the wiring in the main cord/harness was breaking down and depending on how it was bent/moved/wiggled going down the road determined how much current was getting through. New plug and replaced the main 7-wire cord all the way back to the junction box and all brake problems were solved. Old cord looked completely fine externally.
Might be, but seems I was right to look at them. With a 12V battery serving the magnets, all issues resolve. Trucks aren't sending enough power. Trailer will still get a manual adjust but still not sure why a mint condition truck with OEM controller cannot get it done. Controller in the other is obvious because it's rated output is only 5A! What a POS!
So you did inspect the brakes? Adjust them? Test each?
Each magnet should pull 4-5 amps. Hookup trouble truck and see what it outputs. 4k for brakes sounds crazy. But the OEM Dexter stuff is super expensive. Easily $1500 an axle for loaded backing plates and drums. I ended up using some Amazon ones on my Miller, and even those where around $550 for the 4. I had to use the factory drums as there's nothing available... so worn drums were better than no drums. Only other option was putting new spindles, hubs, wheels, tires... far exceeding the trailer's value.
Have not got that far. Other than hooked to truck, fully engage controller, can drag trailer anywhere. Connect 12V battery direct, you have 8 skid marks. The difference is enough to show the primary issue. Will certainly adjust though because as stated, one brake has more wear than others.
Brake size also determines amps required, normally 12g wire is used for multi axle.
But where were you hooking the battery to? Directly into the trailer plug, using a female trailer plug for the connection? Otherwise you are leaving the most failure prone part of the setup out of the equation (trailer plug and socket on truck). Anywhere between the magnets and the truck wiring could be the problem. FWIW, when my trailer brakes were acting up it was the same symptoms on my F250 with integrated controller and behind my IH 4700 or LT9000 with Tekonsha Prodigy brake controllers.
Buddies travel trailer, the brake wire for the right side wheels is run inside the axel tube through a small hole at each end. Eventually the wire for the front axel wore through inside the tube and would randomly short out the brake controller. Took us a bit to find the problem.
Right at the trailer plug of course. Best place to start. Like I say, I just combed and repaired that entire wiring system. I feel good with it. Thus why with a battery weeks ago, I tested the magnet current at each axle. They might be off, but they are consistent. The next step is doing test work on the trucks. Like I mention, I work in electronics so no biggy to build a test device. Honestly probably should make one more elaborate so I can monitor the brake current and voltage over bluetooth. Would make chasing stuff like this easier.
I remember it well: https://www.npr.org/2023/12/05/1196550626/best-of-car-talk-draft-12-05-2023