How does the emergency break away brake system work?

[Brandon2022]

Hello all. I am in the process of restoring a 1978 sovereign from the ground up. It was a mess when I got it with most of the original wiring gone.

I am curious as to how the emergency break away brakes work on airstream rigs. Do the brakes directly receive a constant power supply from the 7-way plug that engages the brake when the electrical signal is interrupted? Or rather, is there some control unit in the trailer that takes care of this?

Thanks for your time!

-Brandon.

[azflycaster]

When the trailer separates from the tow vehicle the break away cable pulls the pin from the switch mounted on the trailer. The switch applies 12 volts from the trailer battery to the brake circuit which should cause all the wheels to lock up.

[jeffb831]

There is a separate cable that is attached to the vehicle. When the cable is pulled from the receptacle by the cable that is still attached to the TV (don't attach the cable to the hitch/receiver in the event that that also detaches from the TV), the circuit is completed and the electric brakes are activated with energy from the batteries. This is why it is required to have at least some sort of battery installed when towing an AS.

[richard5933]

There are two parallel power feeds going to the trailer brakes in an Airstream. The primary circuit begins in the tow vehicle and is controlled by the brake controller there. It sends power to the brakes via the 7-wire cable.

The breakaway emergency system typically feeds the brakes in the trailer by joining with the line coming from the tow vehicle just after where the 7-wire harness wire connects. The purpose of the breakaway power feed is to bypass the circuit originating from the tow vehicle, since when it's needed the tow vehicle won't be there any longer. This breakaway power feed is energized by the battery bank in the trailer.

There is a small switch mounted on the tongue of the trailer with a cable sticking out of one end. When this cable is pulled it completes the 12v+ circuit between the trailer battery and the trailer brake circuit, sending a full 12v+ to the brakes.

[Brandon2022]

Ah ok. That makes sense. Is this feature an airstream specific feature? Or could I find aftermarket components readily?

(I’m ok with having non OEM parts if they are cheaper!)

[JMynes]

Airstream uses the same system every other trailer with electric brakes uses. It’s universal.
The plastic plunger in the switch keeps the contacts separated, keeping the switch open. When the plunger pulls out due to the trailer becoming detached the contacts come together and close the circuit, supplying 12v to the brakes.
Keep in mind, this is NOT a parking brake. The brakes will draw about 13 amps constantly and quickly drain the battery.

[foobar]

Originally Posted by JMynes

Airstream uses the same system every other trailer with electric brakes uses. It’s universal.
The plastic plunger in the switch keeps the contacts separated, keeping the switch open. When the plunger pulls out due to the trailer becoming detached the contacts come together and close the circuit, supplying 12v to the brakes.
Keep in mind, this is NOT a parking brake. The brakes will draw about 13 amps constantly and quickly drain the battery.

And continuous application of the maximum braking current can permanently damage the electric brakes on the trailer.

Just to add emphasis to the statement that the emergency brake is not a parking brake for the trailer.

[Dennis C]

There are stories of hitch failures occurring that cause the trailer to separate from the tow vehicle. They’re rare, but it can happen. I’ve read some of these stories here on these forums. If your emergency breakaway cable is attached to your hitch, then it may not activate the trailer brakes if you have a hitch failure. Many people attach their breakaway to their tow vehicle in another location to avoid this situation. I installed an eye bolt in one of my license plate mounting holes for the breakaway cable.

[SuperTrouper]

Originally Posted by Dennis C

Many people attach their breakaway to their tow vehicle in another location to avoid this situation. I installed an eye bolt in one of my license plate mounting holes for the breakaway cable.

X2 - brad

[cbburke]

While they should be available at virtually any RV outlet here are some examples from Amazon.
https://www.amazon.com/trailer-break...eakaway+switch

[Brandon2022]

Thank you all. The breakaway system makes more sense now. I’ll be ordering and installing one soon and will check back if I run into any problems.

[pegjust]

Yep. We can attest to this. We accidentally pulled the cable pin out and didn’t discover it for 24 hours. It basically killed our batteries (hit 10). Our solar got the batteries back up a bit and we were able to use a few things. Will need to replace them (batteries) this week

[Al and Missy]

Another point - the manual for my Tekonsha Prodigy P3 said that puling the breakaway cable with the umbilical connected to the truck can damage some brake controllers. Do any testing of the system with the 7-way cable disconnected.

[Boxite]

And another point regarding the break-away cable: Do NOT leave Excess Length when attaching the cable….and AVOID those “coiled” types …which are designed to make it easy to attach but allows excess slack to exist in the event of trailer dis-connect from the ball.

Here’s why:

If your trailer comes Off the Ball…. it will hopefully fall onto your crossed-safety-chains. When that happens…the break-away cable should be sufficiently taut to activate your trailer brakes …Immediately… Otherwise the safety-chains will allow so much movement left-right of the trailer-tongue…that a Serious SWAY condition will likely occur…. one that can ROLL your tow vehicle. And unless you are quick-enough to think to manually apply your trailer brakes…(and that’s not likely,…what’s likely is you’ll let up on the accelerator and instantly CREATE a dangerous Sway….)

HOwever, if your break-away cable was properly adjusted it will have applied trailer-brakes…which will immediately pull-TAUT those safety-chains forcing the trailer to closely-follow the two vehicle. It will also instantly notify you of the problem via the decelerating effect the trailer will have on the vehicle.

[Silvr_Bullet]

Researching some of the coiled Brake Cables and the older design, they are both 48” long. So I would question the theory as to which would separate first as they are the same length.

[Boxite]

Originally Posted by Silvr_Bullet

Researching some of the coiled Brake Cables and the older design, they are both 48” long. So I would question the theory as to which would separate first as they are the same length.

The breakaway cable should be adjusted so as to remove excess length. This can be done either by routing it thru the attachment(s) on the vehicle and then back to the trailer…or by mechanically shortening it. I prefer to route it thru the trailer-hitch safety-chain loops….then thru a portion of my vehicle frame…then back to a carabiner kept on the safety-chain storage-loop on the trailer frame.

This allows me to make tight turns when trailering without activating the emerg-brakes… but will immediately activate the trailer brakes should the trailer become disconnected to the ball.

[Silvr_Bullet]

Originally Posted by Boxite

The breakaway cable should be adjusted so as to remove excess length. This can be done either by routing it thru the attachment(s) on the vehicle and then back to the trailer…or by mechanically shortening it. I prefer to route it thru the trailer-hitch safety-chain loops….then thru a portion of my vehicle frame…then back to a carabiner kept on the safety-chain storage-loop on the trailer frame.

This allows me to make tight turns when trailering without activating the emerg-brakes… but will immediately activate the trailer brakes should the trailer become disconnected to the ball.

The coiled Breakaway Cable can be used in the same manner, if desired. Less chance of a snagged then broken or separating cable with coiled type, my opinion from personal experience with a broken old design cable.

[Boxite]

Originally Posted by Silvr_Bullet

The coiled Breakaway Cable can be used in the same manner, if desired. Less chance of a snagged then broken or separating cable with coiled type, my opinion from personal experience with a broken old design cable.

I disagree that an aftermarket plastic, coiled cable is more durable than a genuine metal cable such as is Original Equipment.

If your cable should become snagged for any reason (such has improper routing) then it will apply the brakes…and you will therefore notice and correct the matter…. as long as the plastic type doesn’t snap rather than do its’ job of pulling the switch.

It’s your trailer so you can do as you wish, but it’s fairly well-known that the coiled plastic cables are intended for “ease of use” rather than durability.

Do you still have your Piper? Would you trust plastic flight control cables?

[Silvr_Bullet]

Originally Posted by Boxite

I disagree that an aftermarket plastic, coiled cable is more durable than a genuine metal cable such as is Original Equipment.

If your cable should become snagged for any reason (such has improper routing) then it will apply the brakes…and you will therefore notice and correct the matter…. as long as the plastic type doesn’t snap rather than do its’ job of pulling the switch.

It’s your trailer so you can do as you wish, but it’s fairly well-known that the coiled plastic cables are intended for “ease of use” rather than durability.

Do you still have your Piper? Would you trust plastic flight control cables?

Just to be clear, it’s a cable with a plastic coat on it. It’s less likely to snag as it’s coil will provide some give. The reason the non coiled is provided is because they are less expensive.

[richard5933]

Originally Posted by Boxite

And another point regarding the break-away cable: Do NOT leave Excess Length when attaching the cable….and AVOID those “coiled” types …which are designed to make it easy to attach but allows excess slack to exist in the event of trailer dis-connect from the ball.

Here’s why:

If your trailer comes Off the Ball…. it will hopefully fall onto your crossed-safety-chains. When that happens…the break-away cable should be sufficiently taut to activate your trailer brakes …Immediately… Otherwise the safety-chains will allow so much movement left-right of the trailer-tongue…that a Serious SWAY condition will likely occur…. one that can ROLL your tow vehicle. And unless you are quick-enough to think to manually apply your trailer brakes…(and that’s not likely,…what’s likely is you’ll let up on the accelerator and instantly CREATE a dangerous Sway….)

HOwever, if your break-away cable was properly adjusted it will have applied trailer-brakes…which will immediately pull-TAUT those safety-chains forcing the trailer to closely-follow the two vehicle. It will also instantly notify you of the problem via the decelerating effect the trailer will have on the vehicle.

I fully understand your point here and agree with your theory that the breakaway system should engage as soon as the trailer drops off the ball.

But, this is a controversial topic with valid points to be made on both sides. There is a recent thread where this was discussed ad neuseam so it's probably not necessary to rehash that all. My point is to just mention that there are two seemingly valid viewpoints on this with different manufacturer's of equipment and trailers taking opposing sides here.