what is the correct way to test the trailer "break-away" switch?
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Gary RV_Wizard
Site Team
Assuming the trailer brakes are electric rather than surge-hydraulic...
Yank the breakaway cable hard enough to cause the pin to pull out, closing the switch. Usually that means the pin is literally pulled out, but don't worry - you can stick it back in again. That sends trailer battery power to the electric brakes, causing them to engage. You could try to move the trailer (making it roll), or jack up a side and try to spin the wheel(s) by hand to see if the brake really engaged. The wheel may not be locked but it ought to have form resistance because it should be at its maximum braking force. An alternative "trick" is to hold a compass near the wheel - the brake magnet should strongly divert the needle.
Note that the breakaway requires a functioning battery. If the battery is weak or the wiring corroded, you won't get much braking.
In a surge-hydraulic system, the breakaway cable mechanically pulls a lever to move the hydraulic ram and engage the brakes, just like if you slammed on the brakes in the tow vehicle. There is no magnet at the brake drum, so the compass trick doesn't work.
Yank the breakaway cable hard enough to cause the pin to pull out, closing the switch. Usually that means the pin is literally pulled out, but don't worry - you can stick it back in again. That sends trailer battery power to the electric brakes, causing them to engage. You could try to move the trailer (making it roll), or jack up a side and try to spin the wheel(s) by hand to see if the brake really engaged. The wheel may not be locked but it ought to have form resistance because it should be at its maximum braking force. An alternative "trick" is to hold a compass near the wheel - the brake magnet should strongly divert the needle.
Note that the breakaway requires a functioning battery. If the battery is weak or the wiring corroded, you won't get much braking.
In a surge-hydraulic system, the breakaway cable mechanically pulls a lever to move the hydraulic ram and engage the brakes, just like if you slammed on the brakes in the tow vehicle. There is no magnet at the brake drum, so the compass trick doesn't work.
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Kirk
Well-known member
Gary has given a very good reply. To test my electric brake I used to find a dirt or sand surface area and then first disconnect the umbilical cord and then pull the brake away plug from the switch. With my wife watching the trailer tires, I would them pull it just a foot or so and verify that the trailer was difficult to move and in most cases the tires would slide. Then I put the plug back into the brake-away and reconnect the umbilical cord.
When we had a trailer with surge brakes, (back in our popup days) I also took the trailer and wife out where it was a dirt surface, then I'd pull the safety lever forward and do basically the same test.
When we had a trailer with surge brakes, (back in our popup days) I also took the trailer and wife out where it was a dirt surface, then I'd pull the safety lever forward and do basically the same test.
Joezeppy
Well-known member
I inadvertently tested mine leaving a campground last year. Rounded a sharp corner and the truck stopped dead! The wheels rolled off the pavement a bit so I tried to just gas it thinking I was just stuck in the mud - nope, felt like I was tied to a tree, LOL. Then, I thought maybe I hit the concrete post on the corner - nope, turns out the cable snagged on the 5th wheel hitch and pulled out. Embarrassed that it took me more than a few minutes to figure out what really happened.
On a side note, I found a better way to route the cable to avoid a repeat!
On a side note, I found a better way to route the cable to avoid a repeat!
Ray-IN
Well-known member
been there, done that.
A side note; When the plastic pin is pulled for an extended time, the contacts will get hot enough to melt the plastic housing. A mischievous granddaughter schooled me on that.
merlinmurph
Well-known member
Very timely...
I just brought my TT to my auto mechanic to lube the wheel bearings. While the wheels were jacked up, he figured it was a good time to test the breakaway switch. He spun the wheels, pulled it - and nothing happened. He replaced it.
My TT is now 10 years old and he said the switch was all corroded. Makes sense because I replaced two breakers on the frame last year. I wasn't getting good power because they were corroded, so power-hungry devices like the slide and the power jack would just stop.
Good luck!
I just brought my TT to my auto mechanic to lube the wheel bearings. While the wheels were jacked up, he figured it was a good time to test the breakaway switch. He spun the wheels, pulled it - and nothing happened. He replaced it.
My TT is now 10 years old and he said the switch was all corroded. Makes sense because I replaced two breakers on the frame last year. I wasn't getting good power because they were corroded, so power-hungry devices like the slide and the power jack would just stop.
Good luck!
gwinger
Well-known member
If you do jack up the trailer, DO NOT put the jack under the axles!
Lift it by the frame or the spring mounts on the axles.
As Ray-IN said, don't leave the pin pulled any longer than necessary. Lift one side and pull the pin and test. Replace the pin and do the other side the same way.
Lift it by the frame or the spring mounts on the axles.
As Ray-IN said, don't leave the pin pulled any longer than necessary. Lift one side and pull the pin and test. Replace the pin and do the other side the same way.
DutchmenSport
Well-known member
Pull the pin for the breakaway switch and you'll hear a "hum" at the wheels of the trailer. If you hear the "hum" your brakes are working.
Now, unplug the umbilical cord from the truck, pull the trailer forward while hitched. If you feel the trailer resisting to move forward freely, you KNOW the brakes are working.
It's just that simple.
Now, unplug the umbilical cord from the truck, pull the trailer forward while hitched. If you feel the trailer resisting to move forward freely, you KNOW the brakes are working.
It's just that simple.
xrated
Well-known member
I'm not sure why you would expect a "hum" at the trailer wheels. The hum you are likely referring to is when a contactor/relay/etc that is powered by 120VAC is operating and is commonly referred to as a 60 cycle hum......the frequency of the 120VAC. Brakes on trailers are 12VDC systems and there is no "frequency" or cycles per second.....thus the name Direct Current.
Gary RV_Wizard
Site Team
The brake is a DC electro-magnet, many coils of wire around a core. They can hum as current begins to flow through the coil, but the hum usually stops quickly and isn't always easy to detect. Not an easy or reliable way to detect brake activation, in my opinion.
Alan_Hepburn
Well-known member
Just hold a compass near the wheel and pull the pin - the magnetic field will affect the compass needle...
Ray-IN
Well-known member
But has little bearing on the braking ability. The compass merely indicates a magnetic field is nearby.
Lou Schneider
Site Team
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If the brakes work when they're activated by the tow vehicle they'll work when they're activated by the break-away witch.
Tulecreeper
Well-known member
True, assuming your switch contacts are in good condition.
Lou Schneider
Site Team
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If they aren't you won't get a strong magnetic field at the wheels.
Ray-IN
Well-known member
There can be a strong magnetic field, but if the brakes are not properly adjusted they may not perform well enough to stop the trailer themselves. When the tow vehicle is stopping it also slows the trailer, so weak trailer brakes might go unnoticed until a panic stop is required.
Example; During our Alaska trip my 5er brakes seemed good to me. UNTIL I began the descent down the mountain to Skagway. About ½ way down my dually brakes began to fade. Even though I manually applied full voltage to the 5er brakes I had to use both feet on the brake pedal to stop in the emergency pull-out, even though I had the Allison selector at 1 gear, until the truck reached 10 MPH it didn't downshift.
Turned out the trailer brakes had worn enough to prevent full application, even though I'd adjusted them before leaving home.
From etrailer.com Quote:
"How often do I need to adjust my trailer brakes?
After the initial adjustment, we recommend adjusting newly installed brakes again after 200 miles. After that, you should adjust the brakes every 3,000 miles to ensure they are engaging properly."
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Gary RV_Wizard
Site Team
It's true that a working breakaway switch doesn't prove the brakes are working right, but that's a separate issue. The breakaway triggers the same braking as a hard push on the brake peddle, so if the switch works as designed you get whatever capability the brakes have. Testing for good braking performance is another smart idea, but beyond the scope of the OP's question. And harder to do.
