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Old 09-27-2016, 08:58 AM   #1
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Emergency Braking/Brake Failure

A question popped into my head about my RV and I thought I'd post here to see what people say. I own a 2014 Itasca Solei. It has air breaks, anti-locks etc.

From what I understand there are two independent break systems. But what happens if the breaks fail all-together? There isn't an "emergency break" like in a car. Yes, I can manually downshift the Allison Transmission and apply the engine break. I suppose I'd eventually stop. But is that it?

Just curious - hope it never happens!
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Old 09-27-2016, 09:06 AM   #2
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If there is a total loss of pressure in the system then the spring brake (emergency braking) system takes over and applies pressure to the brakes. This will not happen until the pressure in the lines has dropped below the warning cutoff. You should get plenty of warning per the pressure gauges and then alarms prior to the spring brake actuation. Which should give you enough time to pull over safely with the remaining pressure in the system.
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Old 09-27-2016, 09:24 AM   #3
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It's actually much better than your car, since there is an automatic, spring applied, rear wheel brake that comes on if air pressure drops below a minimum threshold (about 60 psi). It works - I had to use the emergency stop knob once!

So a total failure of the air system is not a cause for worry. About the only total failure that could be disasterous would be physical failure of the rear wheel drum or disc brake mechanism. That would be the same problem if there were a hand-applied brake like on many cars.

My 2013 Buick has some sort of electronic-activated park/emergency brake, just a switch on the console. Not sure how it actually stops the car. No level and cable system, though.
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Old 09-27-2016, 10:04 AM   #4
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When properly maintained, an air brake system is one of the safest systems on vehicles today. Look at the tractor trailers you pass (or pass you) on the interstate. All have the same system as your coach. Also keep in mind if the ABS light comes on you STILL have all normal brake and parking brake functions, You only lose the anti lock feature ......

You coach does in fact have an "emergency brake"...As far as a total air PSI loss, imagine running 55 mph and pulling the yellow parking brake knob out. Once air PSI is lost (drops below the control valve threshold) the parking brake control valve (in the dash) will pop out and the rear brakes will fully apply with about 3000lbs of spring pressure. That's what would happen. The rear wheels would probably lock up and the vehicle go into a sideways skid, but it wouldn't last long. A change in underwear maybe in order, and the coach will not move again until cause of loss of air PSI is repaired or spring brakes are mechanically released from under coach.

Keep your brakes inspected, regular check air system for leaks and you'll not have any issue.
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Old 09-27-2016, 03:55 PM   #5
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so my question is... when was the last time you checked and drained the water from the tanks.... or do you expect the air drier to remove all the water?
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Old 09-27-2016, 06:36 PM   #6
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The air dryer will not remove all condensation from air tanks. Along with simple bleeders that that someone has to pull a cable/chain to release air/condensation from tank there are also available a automatic bleeder that does it, some have 12 V heaters in them as well.

To answer your question, air tanks especially the primary (wet) tank should be drained on an RV at minimum before each trip, or daily in the commercial truck world.
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Old 09-27-2016, 07:11 PM   #7
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If your air brakes break, you could have an accident. An accident caused by no brakes could break everything.
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Old 09-27-2016, 07:22 PM   #8
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The spring brakes automatically apply when the pressure drops to around 15-20 psi (remember your pre-trip check?) The buzzer should come on at 60 psi which means time to stop and check what the issue is. Even f you rip a hose off it takes a bit to empty the air reserve, enough time to quickly pull over and stop.
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Old 09-27-2016, 07:59 PM   #9
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The spring brakes will apply with the equivalent of about 50 psi of air application. That's how much air pressure it takes to compress the spring and reliese them.

You will get a controlled, safe stop, although not as hard as applying the full 100 + psi from the pedal.

You could and we often did move the vehicles, with no air pressure, into the shop. It took a lot of power to get it moving, but it would go.

The two independent systems is referring to the separate front and rear air systems. The have one source of air and share some funtions but have isolation valves between them if, say, one tank gets ripped completely off. The pedal (Treddle) valve is actually two independent valves in one.

All in all, air brakes are pretty safe.
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Old 09-27-2016, 08:47 PM   #10
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Quote:
Originally Posted by stevegster View Post
A question popped into my head about my RV and I thought I'd post here to see what people say. I own a 2014 Itasca Solei. It has air breaks, anti-locks etc.

From what I understand there are two independent break systems. But what happens if the breaks fail all-together? There isn't an "emergency break" like in a car. Yes, I can manually downshift the Allison Transmission and apply the engine break. I suppose I'd eventually stop. But is that it?

Just curious - hope it never happens!
stevegster,
First off, your statement "There isn't an emergency brake" is a bit off. You DO HAVE AN EMERGENCY BRAKE! It's the yellow knob, you PULL for parking brakes and, holding the coach. In fact, IT'S THE ONLY THING THAT HOLDS THE COACH in one spot when you're not driving it, since there is no PARK in the transmission.
And yes, the rear brakes are what's called "Spring Applied" and "Air released". It's been explained by a few here, prior to me putting my two cents in.

But, let me ask you something. Have you ever been driving down the road, especially a country road or, maybe two lane highway in between states with a LOT OF TRUCKS?? I'd bet, while on any of those roads, you've seen, at least once, maybe a dozen times, FOUR skid marks, starting in the center of a lane and trailing off to the side of the road. Sometimes those skids are around 100'-150' long or possibly more.

Those skid marks you've more than likely seen, are the result of the rear set of duals, on the tractor of a tractor-trailer rig, locking up, due to the springs in the rear brake cans, applying the brakes, due to a MASSIVE AIR LOSS, in a short amount of time. In the past, those used to happen quite often. But, in today's air brake systems, there's been many improvements, in all facets of the system. In any case, if you were to loose air while driving, you'd be notified by the systems alarms and gauges, long before it becomes a true emergency. You'll have plenty of time to get that coach to the side of the road.
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Old 09-27-2016, 08:56 PM   #11
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Not to beat a dead horse or be nasty, you would be well advised to get an air BRAKE manual and read up on how these things work. Knowledge is safety!!!
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Old 09-27-2016, 09:45 PM   #12
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stevegster,


But, let me ask you something. Have you ever been driving down the road, especially a country road or, maybe two lane highway in between states with a LOT OF TRUCKS?? I'd bet, while on any of those roads, you've seen, at least once, maybe a dozen times, FOUR skid marks, starting in the center of a lane and trailing off to the side of the road. Sometimes those skids are around 100'-150' long or possibly more.

Those skid marks you've more than likely seen, are the result of the rear set of duals, on the tractor of a tractor-trailer rig, locking up, due to the springs in the rear brake cans, applying the brakes, due to a MASSIVE AIR LOSS, in a short amount of time.
Scott
The skid marks are usually from the lightly or unloaded trailer tires, when the driver pulls the trolly brake handle or his tractors antilocks kick in, when someone cuts him off.

Trailers are not equiped with antilock brakes. Skidding friction is less then rolling friction, so the trailer tends to skid around the non-skidding tractor, off the side of the road. In a worst case senerao, the rig jack-knifes.

Tandem axle tractors have had spring brakes on both drive axles since the 70s. Not to long before then, air brake trucks, had no spring brakes and used conventional driveshaft, parking brakes.

Worked on them all.
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Old 09-28-2016, 10:37 AM   #13
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The skid marks are usually from the lightly or unloaded trailer tires, when the driver pulls the trolly brake handle or his tractors antilocks kick in, when someone cuts him off.

Trailers are not equiped with antilock brakes. Skidding friction is less then rolling friction, so the trailer tends to skid around the non-skidding tractor, off the side of the road. In a worst case senerao, the rig jack-knifes.



Worked on them all.
No doubt you worked on a lot of the older units, but ALL semi trailers manufactured since 1998 must be equipped with ABS also many new semi tractors no longer even come standard with the hand "trolley" valve

https://www.fmcsa.dot.gov/regulation...section/393.55
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Old 09-28-2016, 01:52 PM   #14
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Appreciate the explanations. I'll keep an extra pair of underwear handy just in case!
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