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Old 08-08-2022, 09:37 AM   #1
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Air Brakes

I'm new to the DP coaches and have heard some fairy disturbing conversations concerning the air brakes and what happen should you lose air pressure. Can someone please shine some light on how this coach (1997 Monaco Executive) will react should all air be lost. I'm being told that the brakes will "lock up".
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Old 08-08-2022, 09:42 AM   #2
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Yes, below approximately 40 PSI, the parking brake/emergency brake will apply (spring applied, air released).


This is on the rear axle ONLY and will not lock up the wheels unless on a slippery surface.


Please, please learn about your air brakes and their testing-- much of which is done from the driver's seat.
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Old 08-08-2022, 09:48 AM   #3
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The parking brakes, on the rear axle will apply, because they are held off with air pressure.

They will not lock up and cause a skidding stop.

As you loose air pressure, you will first hear and see a warning. As the pressure drops, the system will still give you enough braking action for a few stops before the spring applied parking brakes come on.

When that happens your rig will come to a controlled stop.

If your in a dangerous situation you can drive thru the spring brakes by flooring the engine and driving a short distance to safety.
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Old 08-08-2022, 10:28 AM   #4
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IMO, an air brake system is superior in its safety design to hydraulic.

Hydraulic relies on hydraulic pressure being present to apply the brakes, so if the system fails due to a leak, you don't have brakes.

An air brake system relies on air pressure to keep the brakes off. So a failure of the system allows you to stop since the brakes will apply with loss of pressure.

I'll take stopping over not being able to.

Do the in-cab air brake test, which can be found by searching on the internet.

While driving, monitor your air gauges. They will fluctuate some as the air bags are constantly adjusting during travel, but the pressure should stay in a fairly tight range. If you notice one or both gauges are dropping abnormally, you should check for leaks. Many times you can hear them.

Leaks are not always immediately critical as the compressor can keep up with small leaks. For example, last year I noticed my front air pressure was lagging the rear in recovery and running about 10 psi lower than it had before. Also, when parking the coach my front bags would drop in about 1 hr (which is still within spec) vs the rears that stayed up. I got under the coach with a spray bottle of soapy water and started spraying each connection point and the bags themselves. Found a leaking ride height adjuster valve and replaced it. Problem solved.

Net, air brakes are a great system. Just be aware of your pressures and at least do the brake check procedure from time to time, though the real recommendation is daily. (commercial drivers need to do it every day, but I suspect many do not.) I printed the by-step procedure and keep a copy in a map holder next to my driver seat.
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Old 08-08-2022, 10:50 AM   #5
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IMO, an air brake system is superior in its safety design to hydraulic.

Hydraulic relies on hydraulic pressure being present to apply the brakes, so if the system fails due to a leak, you don't have brakes.

.
Hydraulic brakes, like air brakes, are a dual system. If you get a leak in a hydraulic brake line you only lose 1/2 the brakes, leaving you a low pedal but still stopping power.

Any hydraulic brake system also has a mechanical, spring or electric applied parking / emergency brake.

Many large DP motorhomes have hydraulic disk brakes. They use them for the superior stopping power and fade resistance over air drum brakes.
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Old 08-08-2022, 12:52 PM   #6
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Originally Posted by dblong View Post
I'm new to the DP coaches and have heard some fairy disturbing conversations concerning the air brakes and what happen should you lose air pressure. Can someone please shine some light on how this coach (1997 Monaco Executive) will react should all air be lost. I'm being told that the brakes will "lock up".
That just isn't so. Maybe on an extremely slippery surface, but it's just the rears that come on with loss of air. Once the air drops to about 35-40 psi the parking brake will come on. (it's powered by big springs, the air keeps the brake in the off position). The parking brake is moderately strong, but nothing like a full application of the service brakes. Plus you get a warning once the air is down to 60 psi or so. Plenty of time to get stopped before the spring brakes kick in.
I have the same coach. Love the air brakes.

Hope you will share pics of your Exec.
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Old 08-08-2022, 01:03 PM   #7
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Hydraulic relies on hydraulic pressure being present to apply the brakes, so if the system fails due to a leak, you don't have brakes.

An air brake system relies on air pressure to keep the brakes off. So a failure of the system allows you to stop since the brakes will apply with loss of pressure.

Either air or hydraulic are both extremely well proven and safe. Last I checked, a Boeing 747 at over 400,000 pounds and a landing speed over 160 MPH has hydraulic brakes! Seem to stop just fine.


And to clarify, the air SERVICE BRAKES (brake pedal) are air APPLIED. It is only the EMERGENCY/PARKING brake that is spring applied/air released and only on the drive axle.
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Old 08-08-2022, 06:46 PM   #8
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Either air or hydraulic are both extremely well proven and safe. Last I checked, a Boeing 747 at over 400,000 pounds and a landing speed over 160 MPH has hydraulic brakes! Seem to stop just fine.


And to clarify, the air SERVICE BRAKES (brake pedal) are air APPLIED. It is only the EMERGENCY/PARKING brake that is spring applied/air released and only on the drive axle.
Good clarification.

My main point was that you don't lose major braking power with the air system.

There have been several cases of large commercial aircraft with hydraulic system failures and thus no braking other than thrust reversers and spoilers which generally results in them going off the runway.

I agree that both systems work well when they work. It's when a loss of pressure failure occurs that I'd rather have the air system design.
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Old 08-08-2022, 07:02 PM   #9
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Originally Posted by dblong View Post
I'm new to the DP coaches and have heard some fairy disturbing conversations concerning the air brakes and what happen should you lose air pressure. Can someone please shine some light on how this coach (1997 Monaco Executive) will react should all air be lost. I'm being told that the brakes will "lock up".

Understanding how spring brakes work
These are only on the rear wheels and do not "lock up" unless you are already stopped, then they become parking brakes.
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Old 08-09-2022, 12:53 AM   #10
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Yes, below approximately 40 PSI, the parking brake/emergency brake will apply (spring applied, air released).


This is on the rear axle ONLY and will not lock up the wheels unless on a slippery surface.


Please, please learn about your air brakes and their testing-- much of which is done from the driver's seat.
actually its 60 PSI, get below 60 and POP goes the knob If yours doesnt pop until 40, you better replace that valve
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Old 08-09-2022, 04:06 AM   #11
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I suggest you take the air brake course even if your state doesn’t require it to drive a m/h with air brakes. It’s relatively cheap, takes the better part of a day and gives you a good idea how everything works and how to preform basic adjustments and checks.
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Old 08-09-2022, 05:37 AM   #12
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actually its 60 PSI, get below 60 and POP goes the knob If yours doesnt pop until 40, you better replace that valve
No, they don't apply at 60 PSI. Here is a screen shot from CA DMV.Click image for larger version

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Old 08-09-2022, 08:17 AM   #13
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No onereally answered the question/concernÖ

Dont be afraid or concerned. As said above, the air brake system is well known and reliable. Yeah, leaks do happen, but very rarely, and they are easily detectable, and only the very worse ones will cause the parking brake to pop (you usually have a LOT) of warning for days or weeks that something is going on.

Maybe the biggest thing is do *not* pump the brakes (that causes rapid depletion of air pressure), instead braking technique is a single long push with the pedal held down.

Ive driven long flat miles, and been up and down many mountain grades Ö and air pressure has never gotten critically low.

As said above, take a course or study online videos on managing air brake systems. *also* study online material on how to use your engine gears and exhaust brake to descend steep grades (you want to use your air brakes *very* minimally on those..)
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Old 08-09-2022, 08:22 AM   #14
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actually its 60 PSI, get below 60 and POP goes the knob If yours doesnt pop until 40, you better replace that valve
The visual and/or aural warning will be at 60 psi BUT the park brake knob will not pop out til approximately 40 psi.
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