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Open Roads Forum  >  Travel Trailers  >  General Q&A

 > Brakes grabbing

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katysdad

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Posted: 09/12/22 06:19pm Link  |  Quote  |  Print  |  Notify Moderator

hopefully OP has solved problem. If not I have seen wires get loose or pulled out of replacement 7 way plug on trailer pigtail and short or power a circuit inadvertently. Wintertime towing can fill them with road chemicals and corrode all the connections in them also. Always recommend replacing with new cord and molded plug.


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JRscooby

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Posted: 09/13/22 04:34am Link  |  Quote  |  Print  |  Notify Moderator

katysdad wrote:

hopefully OP has solved problem. If not I have seen wires get loose or pulled out of replacement 7 way plug on trailer pigtail and short or power a circuit inadvertently. Wintertime towing can fill them with road chemicals and corrode all the connections in them also. Always recommend replacing with new cord and molded plug.


A molded cord is a good idea. I have had good luck by after checking to make sure all is good, then putting enough silicone sealer to fill the cap. Water can't get in, and nothing can shake loose.

Grit dog

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Posted: 09/13/22 06:39am Link  |  Quote  |  Print  |  Notify Moderator

JRscooby wrote:



A molded cord is a good idea. I have had good luck by after checking to make sure all is good, then putting enough silicone sealer to fill the cap. Water can't get in, and nothing can shake loose.


Lol, now that’s a real trucker fix goober job.


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JBarca

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Posted: 09/14/22 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

MFL wrote:

Hey JR, this is a common issue, but normally takes at least a light touch of pedal, that can result with braking similar to pulling the pin. Very aggressive, tires chirp/maybe smoke. As Grit mentioned, turning the gain way down will help, but braking will be diminished.

It starts mostly intermittent, due to the wiring moving/bouncing inside the tube.

Quick fix..cut the wires going through tube, and run new cross wire outside the tube.


Hi Guys,

I might learn something new here, but please help explain how the brakes can grab hard when the hot wire in the axle tube shorts?

Here is from my background to help the cause. The chaffing is real. What I cannot sort out is how the brakes grab real hard close to lockup as you are stating.

My findings:

Yes, as the trailer ages and the towing miles increase, the double wire lamp cord style cable inside the axle tube creates a wire insulation chaffing problem. First is, the insulation gets brittle over time. Circular cracks in the insulation happen, mostly where the wire flexes but it is not limited to just the flexing areas. Moisture can then get to the conductor given the right conditions.

The middle area of the axle tube is prone to the wire bouncing and rubbing over time. The wear is not selective to which wire wears to expose the conductor.

Here is one of the many I have found while restoring older campers.
[image]

A close up showing the tarnished copper exposed
[image]

The hole area at the ends of the tube also can have exposed conductors also. This wear is different then the mid tube area. The brittle wire cracks where the wire rubs the tube hole edge, starts to wear/vibrate into the conductor.

Now, when the exposed conductor touches the metal frame, it is sort of a 50/50 good luck or bad luck which conductor touches the tube.

If the chassis ground wire wears through and touches the tube, this issue may not be found under normal operating as one side of the brake coils are tied to chassis ground. I have not seen this be a problem short of the wire wearing all the way through and creating an open ground on the brake coil. Or a weak ground and the magnet not getting full power.

If the brake hot tire wears and touches the tube, when the brakes are applied here is where problems can start. And where I need someone to help explain how the voltage and current above normal braking to get high enough to create hard breaking on all wheels or even one of them.

The average brake coil on a 10" x 2 1/4" all the way to a 12" x 2" or 12 1/4 x 3 3/8", drum ID x show width, brake has an magnet coil ohm reading around 3.2 ohms. Its not much but it can create 3 amp draw on a full 12 volt power circuit. There is a load there and not a dead short.

When the chaffed wire touches the axle tube, that can be close to a dead short or a less pending how much corrosion resistance is on the tube.

How does the truck brake controller send full voltage and current similar to a emergency break away switch activation with only a light tap of the brake pedal? What tricked the controller to know to do this?

On a time based controller that only uses the brake pedal switch, it is a timed response for when full current is reached according to the gain setting.

On a proportional controller, well this depends on the brand and type. The pendulum ones, need the truck angle change to create high power.

The newer truck integrated ones which us the master cylinder pressure, that is something different too.

What an I missing on how all 4 or 3 of the 4 go to full power when one is grounded out on the hot wire?

My original thought was the controller senses the dead short and tries to protect itself, maybe shutting down the power to not have it burn out? What happens next I'm not sure. Help fill in the details on how the full power is created like you are stating.

Thanks

John


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MFL

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Posted: 09/15/22 06:12am Link  |  Quote  |  Print  |  Notify Moderator

Hi John...since this thread is now dead, I will try to explain my personal wire chafing experience. I do need to admit that, I never made a living, or made my house payments repairing trailer lights. [emoticon]

Several trailers ago, on my Damon Challenger FW, my trailer brakes were intermittent, working normal, then hardly at all. IIRC, I would get improved braking by turning up the gain, on the Tekonsha Voyager I was using. Braking seemed okay, for a while, until the next time, just a light touch of the pedal, and trailer tire/tires squealing. I think the very chafed wiring in the tube, would shift at times, changing the contact to axle tube, causing too little braking at times, to severe the next.

I checked the wiring going through the rubber grommet and noticed some chafing, so decided to replace. Now I noticed major chafing, when removing the brittle wiring from inside the tube, which was easily making contact at times.

I replaced complete cross tube wiring, and my problem was solved.

BTW John: I have always thought you to be a respectful, and very helpful member of this forum. It's the reason I took the time to explain my experience. [emoticon]

If you learned anything IDK, but a smart man, like you, keeps an open mind. I could not believe another poster, claiming to be a back alley trailer repairman, thinking it's not possible to have chafing, inside the axle tube.

I learned something from this thread, due to OP posting about replacing the emergency switch, solved the problem. I was not believing that his brakes were grabbing, without even a touch of the pedal.

Have a great day!

Jerry





JRscooby

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Posted: 09/15/22 06:40am Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

JRscooby wrote:



A molded cord is a good idea. I have had good luck by after checking to make sure all is good, then putting enough silicone sealer to fill the cap. Water can't get in, and nothing can shake loose.


Lol, now that’s a real trucker fix goober job.



Well if a mass produced cord will work for you, good. And if your boss sells the molded cords, you can't suggest anything else could work. But if you need the tongue to be over 20 feet long, and expect to drag that tongue out of a pile of material, you don't want splice or junction box at the end of a store-bought cord.
Nearly fill the cover, put it back on, wipe of what is pushed out, and somebody looking close enough to see it deserves to find something wrong.
If a "real trucker fix goober job" can last doing that kind of work, most RVers will never have a problem unless they drag it. And BTW, dragging will kill a molded one too. Cut it off, save the rest of cord.

JBarca

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Posted: 09/15/22 06:42am Link  |  Quote  |  Print  |  Notify Moderator

Hi Jerry,

Thanks for your background explanation. It helps.

I can see the weak braking, that adds up. I'm still trying to sort out on how the extreme braking is happening. H'mm, I have to think in this some more. Somehow the brake controller is reacting to the shorting of the hot wire.

The wire chaffing issue, for sure a problem. For those wanting to keep an older camper to still be towed from camp to camp, yes, just abandon the wires in the axle tube and upgrade the wiring outside the tube. 10 years towing is what caused the wear in the pic I posted on the one I was restoring.

The emergency breakaway switch, yes a forgotten safety feature. Again, restoring older campers, they where never changed since the day it left the factory. And they do not get on the annual maintenance list to pull and check them, and put silicone spray on the O ring. If one reads the instructions that comes with the switch, many brands recommend changing them every 3 to 5 years. They really do not have a lot of faith in them. I have found the switch most times corrodes inside and creates extreme heat the day it ever gets pulled, to the point the insulation can started melting. The O ring cracks over time, the pin gets jammed in, or water leaks in and kills the switch. That said, I have not seen one yet that corroded on. I know it is not impossible, maybe just not as common.

Happy camping

John

opnspaces

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Posted: 09/15/22 08:44am Link  |  Quote  |  Print  |  Notify Moderator

In MFL's explanation I can see the heavy braking. If he has chafing in of the insulation and the inside of the axle tube is rusty he has an intermittent high resistance short. So when he applies the brakes some current goes to the magnet and some current goes into the rusty axle tube causing weak brakes. Since the brakes are weak he cranks up the gain on the controller to compensate. Next road bump and the wire moves and is no longer shorted to the tub. Now when he touches the brakes he gets the full voltage at the brakes locking them up.


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JBarca

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Posted: 09/15/22 09:15am Link  |  Quote  |  Print  |  Notify Moderator

opnspaces wrote:

In MFL's explanation I can see the heavy braking. If he has chafing in of the insulation and the inside of the axle tube is rusty he has an intermittent high resistance short. So when he applies the brakes some current goes to the magnet and some current goes into the rusty axle tube causing weak brakes. Since the brakes are weak he cranks up the gain on the controller to compensate. Next road bump and the wire moves and is no longer shorted to the tub. Now when he touches the brakes he gets the full voltage at the brakes locking them up.


Yes, I agree with your thinking would do that. Turning up the gain can do it.

The open question now is, did MFL turn up the gain? If he never touched the gain, then there is still something else going on not yet understood.

* This post was edited 09/15/22 09:37am by JBarca *

MFL

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Posted: 09/15/22 09:37am Link  |  Quote  |  Print  |  Notify Moderator

Yes John, if you read my post above, I did turn up the gain, due to braking being unusually poor. If you are familiar with the older Voyager, the gain had no real sequential marking. Mine was always set about 1 o'clock, worked great, but as braking diminished, probably set to 4-5 o'clock?? No real measure on this model.

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