I just went through a big fiasco yesterday trying to get the brakes to hold on a tandem axle dually trailer with 10,000 lb axles.

They only come on just enough to get warm if you put them on full for a few miles or when stopped you can just feel the slightest resistance.

All four work about the same.

I opened one up and discovered oil on the drum's magnet surface. We cleaned everything and checked the magnet for magnetizm while apart. Shoes are good and adjustment is close. We packed the bearings and replaced the seal to try again. No difference. So I connected a fully charged new group 27 battery to the magnet wires on the outside of the backing plate and still, only the slightest dragging.

My controller shows 4.8 to 5 amps going to the braking circuit for all for wheels.

So. Can the magnets become weaker while still working? Can they all become weaker at the same time? It seems like there is very little wear on both the magnet surface and on the brake shoes. Everything looks just fine. But there was some rust on the shoe pivots and linkage so I pushed them around and sprayed some with WD-40 to make sure there was no sticking. When they do come on, their slight little bit, they also release just fine.

What's up with this thing? Meanwhile, I have a Skytrak waiting on the trailer 130 miles away from home and 220 miles from the job. Just to clarify, I bought the Skytrak, and borrowed the trailer to haul it, 130 miles from home. Now I'm back and deciding what to do next.

Looks like I'll be finding someone else to haul it for me .

 

i started to tell you you do not need trailer brakes to haul it then i noticed the auto. i never figured out what one might be good for. back to your brake problem. check for corroded 7 pin plug. best way hold the brakes full on for two minutes then feel the plug and socket feel all four magnets the plug and socket should be cold and the magnets warm. after this you are going to need a voltmeter and a 40 foot piece of wire. connect one side of wire and other side to volt meter. next go to a magnet, with some one holding the brake full on check the voltage on each wire. if grounding is bad the ground wire will have a few volts on it if there is less than 10 or 11 volts on the hot leg start tracing it back toward the truck

 

oops connect the wire to the negative side of the battery

 

Magnets are bad... Need replaced

 

You might need to get the drums resurfaced and the ring where the magnets come in contact with the drum.

 

Carl,

Are you trying to say that if my pickup had a stick I wouldn't need brakes on a 19,000 pound trailer? I can't believe anyone would say that unless they were only going a mile or two on a flat road with no traffic. This is a 220 mile trip through the Sierras. I've since decided I don't want to tow it even with perfect trailer brakes.

I bypassed all the electrical in the trailer completely and connected directly to the magnet wire on one wheel with only the slightest brake response. The magnet does work though, as we tested it while apart. I'm showing up to 5 amps from the trailer brake controller to the trailer. It's it doesn't seem to be a trailer wiring problem but I don't know how many amps it should draw.

Slim,

The surfaces are in very nice condition. Almost like new. Nothing wrong there. It is evident that the magnets are making contact with the drum, and the shoes are too, because everything is polished up nicely, but not severely worn or galled.

Since it works, but only slightly, it seems like the brakes are being only slightly applied. As though it has low voltage. But it's not low voltage. Have these magnets ever been made in 24 volts? Seems bizarre, but that's what I would expect from them.

Also, all 4 are working about the same with one being a little weaker. How could all 4 magnets fail partially? Doesn't seem likely. It seems they will fail or not electrically. Or they will wear through and short out. Not these.

 

it comes to mind that the brakes are installed backwards... try backing up with the brakes applied

 

johnh,

That is an excellent thought and would produce the symptoms. I did not think of that before, but I did back up during testing several times and for several hundred feet. No difference.

Installed backwards. Good idea and I wonder how many times that has happened.

Thanks.

 

i have a trailer that we changed the axles out on twenty years ago and was going to order brakes for it. still have not got around to it. we haul heaver loads than that all the time in the mountains. with the stick you find a gear you can descend the grade with out ever touching the brakes. a bd or pac exhaust brake will let you get one gear higher. drive this way even with trailer brakes and you will be amazed at how long the brakes will last. dis connect the four magnets and apply 12 volts to each one the draw should be the same for each at about 1.5 to 2 amps then remove the magnet and check for rust blocking the engagement i have had this happen several times. back to the auto if you spend about $10,000 with bd to upgrade it and add a bd brake you can tow with it and it will be nearly as good as stick, or so my neighbor tells me.

 

It sounds like adjustment to me. I always adjust them till they stop then back off till they turn. Each magnet should draw about 3 amps so for 4 brakes that'd be 12 amps. Here's the quote directly from Dexter's website.

"BRAKES - How do I measure brake current or amperage?
Dexter 7" brakes draw about 2.5 amps per brake and all other brake magnets draw about 3 amps per brake. The total system amperage is calculated by multiplying this number by the number of brakes/magnets connected to the brake system. To measure the brake current, the engine of the towing vehicle should be running. Disconnect the wire at the point that you wish to measure the current draw and put the ammeter in series with this line. Make sure your ammeter has sufficient capacity and note polarity to prevent damaging your ammeter."

 

david,

Thanks for that. I didn't know how many amps they were supposed to draw and I'm only reading 4.8 to 5 for all four on my Brakesmart. I have continuity on the one I had apart and even hooked up directly to that one magnet the system barely comes on. I wonder what the ohm reading is supposed to be on each one.

I'll search around some more and then head back up to the trailer with some new magnets. They seem to be not a common style and are rather large. Each axle is rated for 10,000 lbs.

 

Am I reading this wrong? Or do you really tow a 20,000 pound trailer without trailer brakes?

 

They should read about 4Ω each.

Is your Brakesmart gain turned all the way up?

 

david,

Thanks for the ohm reading. And yes my Brakesmart is turned all th eway up. Plus I went directly to the magnet wire, at the wheel, with another power soure and got no better results

I'm not up there now and am about 130 miles away so it's gonna have to wait a few days.

Thanks for the response.


Utundra,

I too am amazed that someone would deliberately tow in the mountains with 20,000 lbs behind a pickup and not care about trailer brakes. And tell someone else they are not needed! No offense Carl, but that is suicidal and dangerous to everyone else on the road. Maybe a few miles on level ground with no traffic, but out on the highway with traffic, hills, merging, and people not paying attention? No way. Try stopping on a curve or straightening the trailer if it starts to fish tail a bit. Not without trailer brakes.

 

Raspy, sorry if this is a repeat but make sure your ground from the trailer is going to the battery on the tow vehicle. Allot of the time folks ground to the frame and expect that the connection through the ball is sufficient, it's not. You should ground the brake wire on the trailer to the trailer frame AND the grounding terminal on the trailer plug. On the tow vehicle, do the same. The reason behind this is that if you lose one ground, you still have one, albeit weak.

Also, on the Brakesmart make sure your power factor is turned up. With the load you're looking at you might want to increase the initial brake constant as well.