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Old 07-30-2012, 08:43 PM   #1
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Air brake pressure

On our 2003 Itasca Horizon DP, after sitting 2-3 days in the campground with airbags deflated, on initial startup the low air horns come on and I can watch the gauges front and rear, seems like when it gets to around 40 lbs the horn will go off. I typically wait until it is about a 100 lbs front and rear, put my foot on the foot brake and release park brake (yellow knob on dash). At that time the rear gauge starts deteriorating and drop down to as little as 50 lbs. Within a minute or so it is fully recovered. Front gauge does not deteriorate. At cruise both hover around 125 lbs. Is this drop normal?
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Old 07-30-2012, 08:59 PM   #2
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Yes. You are using air when pressing the brake pedal. May want to wait till pressure builds all the way before releasing parking brake, plus it gives you another chance for a final 'walk around checking your lights and signals while checking for anything missed.
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Old 07-30-2012, 09:03 PM   #3
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The drop in air when sitting is a leak someware it's a small one but it is leaking down most will over time. when you first start it up let it build up all the way till it spits then you know it's full, when you push button in it will drop again the pump will come back in around 90 psi and top off at 120 to 125 psi now you have air brakes and air ride it takes a few min to air everything up, it's running normal
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Old 07-30-2012, 10:06 PM   #4
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Missymoto,
Hopefully I can help shed some light on your question.

First of all, I always let my DP engine run or warm up until the air dryer discharges which is a noticeable sound which is the release of air as a result of the air compressor govenor cycling which unloads the compressor. This lets me know that the air system has charged the reservoirs to a full capacity.

When you step on the brakes, that action consumes a fair amout of air to pressurize each of the service air brake chambers. To compound the air consumption, when you release the air parking brake by pushing down on the mushroom button on the parking brake control valve, the air system must pressurize the each of the parking brake chambers of the dual diaphram brake chambers that are attached to the rear drive axle. The combination of the two actions you described will definitely consume some air from the air reservoir(s) depending on how the vendor has plumbed the primary and secondary reservoirs, which are sometimes also referred to the front and rear reservoirs.

In an effort to help you evaluate your air brake system I have attached a pdf document that I have modified somewhat for my own use. It will hopefully give you some excellent air brake inspection and testing guidelines that will assure you of having a safe trip with your RV, and give you comfort of mind knowing that everthing is functioning as required.

Hope this information helps and happy RV'g

Jack
Attached Files
File Type: pdf Air Brake Inspection & Tests.pdf (169.5 KB, 200 views)
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Old 07-30-2012, 10:36 PM   #5
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I would suggest an air brake course, or at least getting an airbrake manual from your local DMV. Having the knowledge of how these systems work, and how to maintain them is crucial to safety. I am not saying this to be nasty, but after driving commercial rigs for years I have seen the results of lack of air brake training.
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Old 07-30-2012, 10:59 PM   #6
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In some jurisdictions an air brake endorsement (to your DL) is required. The endorsement requires that you take an eight hour course, which included classroom & practical exercises and also requires you complete & pass both a practical & written exam. Prior to taking this course I couldn't for the life of me imagine how it could take an entire day to learn about brakes. Well I did learn an amazing amount of information about an extremely important component of our Coach. I would recommend everyone with an air brake equipped Coach consider taking such a course.

While, on one hand, I am glad you do not need a special license to legally operate a MH in my jurisdiction, on the other hand, I am still shaking my head that as long as I could write the cheque....I could"legally" drive-off in 38' of +30,000lbs vehicle towing another couple of thousand lbs of towed vehicle at a total length of around 60'! In a totally objective sense.....how crazy is that? How can anyone argue that we shouldn't need to complete some training and demonstrate an acceptable level of operators skill ( an RV operators endorsement to your DL) in order to safely operate one of these things?
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Old 07-31-2012, 10:55 AM   #7
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air hissing under dash.

I have a charleston forest river DP.there is a hatch on the dash and if you pick it up there is a black dial with airlines going to it.while there is air in the system it hisses.i dont know if this is normal or not.air pressure front and rear is fine and i dont see any problems i would just like to know what it is for and if i am supposed to do something with it.i would think if its normal they would have put it somewhere you cant hear it all the time.any help or info?
thanks guys
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Old 07-31-2012, 02:33 PM   #8
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missymoto:
Here's a good airbrake manual.
http://www.mpi.mb.ca/PDFs/AirBrakeMa...alComplete.pdf
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Old 07-31-2012, 03:38 PM   #9
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"I have a charleston forest river DP.there is a hatch on the dash and if you pick it up there is a black dial with airlines going to it.while there is air in the system it hisses."


There should be no "hissing" of air under the dash. You have a leak that should be investigated.
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Old 07-31-2012, 04:46 PM   #10
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I think your system is working as designed... but don't your air bags deflate automatically when you level the coach? Good advice on allowing your system to completely air up before doing anything.

The air brake reading material provided above is great information and I found that learning about how the air brakes worked was really pretty interesting. I'm not sure it changed much about how I drive but I feel better knowing how something that important actually works.


Quote:
Originally Posted by Jack1234 View Post
In some jurisdictions an air brake endorsement (to your DL) is required. The endorsement requires that you take an eight hour course, which included classroom & practical exercises and also requires you complete & pass both a practical & written exam. Prior to taking this course I couldn't for the life of me imagine how it could take an entire day to learn about brakes. Well I did learn an amazing amount of information about an extremely important component of our Coach. I would recommend everyone with an air brake equipped Coach consider taking such a course.

While, on one hand, I am glad you do not need a special license to legally operate a MH in my jurisdiction, on the other hand, I am still shaking my head that as long as I could write the cheque....I could"legally" drive-off in 38' of +30,000lbs vehicle towing another couple of thousand lbs of towed vehicle at a total length of around 60'! In a totally objective sense.....how crazy is that? How can anyone argue that we shouldn't need to complete some training and demonstrate an acceptable level of operators skill ( an RV operators endorsement to your DL) in order to safely operate one of these things?
X2

It's amazed me too... especially since I had to get the motorcycle endorsement on my license and had to go through a ridiculously difficult riding test and almost failed... which would have been embarrassing since I raced the darned things for ten years.

Rick
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Old 07-31-2012, 07:29 PM   #11
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Quote:
Originally Posted by dons2346 View Post
"I have a charleston forest river DP.there is a hatch on the dash and if you pick it up there is a black dial with airlines going to it.while there is air in the system it hisses."


There should be no "hissing" of air under the dash. You have a leak that should be investigated.
Well the knob i am talking about seems to spin with a plus and minus,the hole that is hissing is on that knob,looks like some sort of adjustment of air pressure but i just dont know why air is coming out of the hole in it.....
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Old 07-31-2012, 07:36 PM   #12
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Quote:
Originally Posted by km17

Well the knob i am talking about seems to spin with a plus and minus,the hole that is hissing is on that knob,looks like some sort of adjustment of air pressure but i just dont know why air is coming out of the hole in it.....
I'd be surprised if it had anything to do with your brakes....more likely your suspension. Who made your chassis? You might want to post this question toyour chassis forum or call the chassis maker.....or Forest River. Maybe post a picture. Good luck.
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Old 07-31-2012, 10:18 PM   #13
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Quote:
Originally Posted by Jack1234 View Post
I'd be surprised if it had anything to do with your brakes....more likely your suspension. Who made your chassis? You might want to post this question toyour chassis forum or call the chassis maker.....or Forest River. Maybe post a picture. Good luck.
Yeah i will do that thanks
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Old 07-31-2012, 11:02 PM   #14
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Quote:
Originally Posted by km17 View Post
Well the knob i am talking about seems to spin with a plus and minus,the hole that is hissing is on that knob,looks like some sort of adjustment of air pressure but i just dont know why air is coming out of the hole in it.....
Just a guess: If you have an air pressure operated step well cover, it may be the adjustable mac valve that moves the step well cover. Mine does not have a knob, but has an adjustment screw instead.

Fred
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