Brakes, dilemma.

Ok my terminology is wrong, but the op states there getting power to 3 of the 4 hubs without doing anything using the compass test. So, no pin pulled , no brakes applied and hes showing 3 hubs with power. Not 3 hubs with power while depressing the brake or pulling the pin on the breakaway switch. Im only going by what they posted. I totaly get and agree with what your saying, but the op is stating the opposit. It dosen't have to be full power there getting to ware the shoes, just a little to enguage them. As you said, the test just shows power, not how much. Thats where the meter comes in. If you ever saw a seized brake caliper on a car, it dosen't always smoke or cause any other problems then worn pads. Without the op coming back to clarity, I can only go by what they said.

If properly used, the compass can tell you that the magnet is working.
Hold a compass close to hub, below center but above bottom of drum. The magnetic needle will point to hub (No Zee, your fone will not work) Move compass away until needle points back north. Have helper apply brakes, the needle should swing back towards drum. Now this will not tell you everything, but will tell you the circuit is good enough for magnet to move the needle.
Now the OP has not reported smoke, bearing or tire failure, so it is safe bet when let off brakes, all are released.
You and 3 of your friends are carrying a pool table. 1 stops to take a phone call, can you and 2 handle the load? Maybe, but lot more strain. The OP has 1 brake on the phone.
Electricity likes to be where it's at. If it can't see a way to get back, it won't go anywhere. A open circuit means there is no way for it to go around. There is no open on the 3 that work
Decades of working on automotive electrical, most problems come from using the chassis for ground, so the first thing I would look at would be where the wire hooks to ground. It might be a short, but most likely somewhere between where that wheel circuit branches off and ground there is a open circuit.

But if the compass test works, and I can only go by information I'm given, then they have power to 3 of the 4 brakes. How much is unknown. This would also cause premature ware on those 3 assemblies. It would also exclude a faulty break magnet on the good pad assembly. So that leaves an open wire feeding power to the other 3.

I agree with what JRscooby has been saying. With one brake not working the controller would need to be set to a higher level and then cause the brakes that do work to wear more quickly.

There were a couple others on this same track, but the rest of you are making this more complicated than it is.

The OP needs to figure out why that one magnet is not working. Whether it be a bad magnet or a wiring issue.

I just assumed he needed a high setting because 25% of the trailer brakes don't work.

bucky wrote:

bgum wrote:
We usually run on 3-4 with prodigy p3. Boost set at 1-2. You may be running a little too high. Is your 5th wheel pushing the truck when braking?

The trailer would not be pushing the tow vehicle in this scenario. It would be the opposite.
As to pulling the safety switch and worrying about the controller just get somebody to push the brake pedal for you while hooked up.

It appears you misunderstood my underlying question as to why he has his brake controller set that high. Does/Did he feel that way and therefore set it high.

Brakes wore out on 3 out of 4 wheels, in a distance that a aggressive diver could go thru a set of shoes,(considering trailer shoes start much thinner than back in the day when a high performance car had all drum brakes, the mileage is not that far out of line). Now you want to tell the world the most likely problem is with the 3?
If the OP has had a bunch of trouble with bearings and blowouts, I would look into "Are brakes getting power when they shouldn't", but with the info I have the first thing I would look for would be 1 of the no-strip Scotch-lock connectors. Next would be where brake is grounded. Next would normally be check right where wire connects to magnet. (Had drum off, should of checked then) Next look at connection where that wheel Ys off the others.

JRscooby wrote:

schlep1967 wrote:
Come on people. READ THE ORIGINAL POST.
His brakes wore out prematurely. That doesn't happen if his brakes don't work.
It happens when they are engaged and shouldn't be.
Most likely case would be driving with a foot resting on the brake.
After that I would look toward a short on the tow vehicle providing voltage to the brake circuit. Test at the trucks seven pin plug.
If it was the emergency breakaway the battery on the camper would be dead unless it is plugged in any time it is not hooked to the truck.

I read the OP. All my posts have been critical of what he has been told about the hunt for the problem. And you are right, the probability of the problem coming from Break-away-switch is 0.
And the chance there is a issue with driving style might be pretty good, but that is not the only problem.
3 out of 4 brakes wore out. Fact is 25% of brakes not working will cause rapid wear to the ones that work.
And once he has looked at the shoes, he knows which wheel has the problem. And if somebody that knows what the are doing replaced them, about the only place the problem can be is electrical, and in the branch going to that wheel, or ground.

The problem is we don't have all the details. He had power at 3 brakes with the breakaway pin in. So does he have a problem at one wheel or three wheels? Did he have the truck umbilical hooked up at the time of the magnet test? Where is the voltage coming from? the onboard battery or the 7 pin plug?
I agree that the one brake that was not worn out is not acting as the others, has a problem. But ... if no brakes are being applied none of the brakes should have power. It is likely there is more than one issue going on here.

All the compass test will tell you is that there is a magnetic field that will cause the needle to swing toward the wheel. Take the current from the brakes, and the magnetic field goes away, and the needle will go back to indicating magnetic Earth north. Make sure the trailer is oriented so that needle will swing away from magnetic north.

If you have one that does not swing the needle, the magnet is not connected or the magnet is bad. The breakaway switch will apply the full battery voltage to all the brakes. Start by looking for a broken or loose wire.

As for the controller setting, it is specific to your truck and trailer and will often need to be changed as the trailer brakes get some wear.

Ken

I read the OP. All my posts have been critical of what he has been told about the hunt for the problem. And you are right, the probability of the problem coming from Break-away-switch is 0.
And the chance there is a issue with driving style might be pretty good, but that is not the only problem.
3 out of 4 brakes wore out. Fact is 25% of brakes not working will cause rapid wear to the ones that work.
And once he has looked at the shoes, he knows which wheel has the problem. And if somebody that knows what the are doing replaced them, about the only place the problem can be is electrical, and in the branch going to that wheel, or ground.