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Old 09-22-2009, 12:15 PM   #1
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bleeding air brakes

Not entirely sure on the "bleeding" process. Couple questions:
Do you do it in the morning with the engine running....at night after jacks are down and engine off...how about emergency brake...etc.


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Old 09-23-2009, 09:18 AM   #2
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Bleeding brakes is for hydraulic brake systems rather than air brakes. Bleeding air out of an air brake is, uh, kind of pointless, right? I've heard that sometimes water can get in the air system and that should be blown out. The preferred way to do that is from the water drains in the air reservoir, rather than the brake lines. Is that what you meant by "bleeding"?.

I think the air brake lines essentially vent themselves, every time the brake pedal is released. A valve opens and the air pressure is released, dropping the pressure in the lines to zero and dumping whatever air was in them.

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Old 09-23-2009, 01:59 PM   #3
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Bleeding air brakes is probably just the wrong way to say "draining the air tanks". In the old days truckers would drain their air tanks evry morning before leaving on atrip. That's because all of the moisture and oil would settle in the air tanks. You need to drain that stuff out so that it doesn't eat away at the rubber brake diaphragm components.

Today, air brake systems have an air drier. The air drier will filter that stuff out. Most of it settles into the collecting reservoir below and gets automatically drained by the purge valve whenever your compressor's air governor unloads. The coalescing filter further prevents "stuff" from getting into the air tanks. Air tanks may even have automatic drain valves on them but I wouldn't trust them.

There are generally three manual drain valves on a DP. They are actuated by pull cables in the front wheel wells. Tug on a cable and the valve will spit out whatever is in the tank. Most owner's manuals still refer to daily tank draining but it's really not that necessary any more.
your air drier filter is rated for either 2 or 3 years under average conditions. If you live in a swamp you'll find that the filter dies much sooner than if you live in the desert.

I drain my tanks once a month. The reason is not to dump moisture and gunk out because there never is any. The drier takes care of that. The real reason to drain them is to test to see if your air drier is working. One day you'll see a bunch of moisture spit out the bottom and you'l know it's now time to service your air drier and replace the filter element. So, basically think of it as a testing or diagnostic procedure rather than an actual service task.
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Old 09-23-2009, 03:59 PM   #4
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bleeding air brakes

thanks cruzer....you got the right idea. i could have phrased it much better.
So, when you bleed once a month...do you do it at the start of the day with the coach parking brake on and after the "buzzer" goes off indicating good air pressure....or what.
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Old 09-23-2009, 04:23 PM   #5
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It's best to drain the air tanks when they are at full pressure. If the pressure is down, start the engine to build up pressure. Because most drain lanyards are inside the front wheel wells it's also handy to have the air bags pumped up so that you can get to them easier. For safety purposes I'd recommend not sticking your arm in there. If something should go wrong and the coach would settle down you may get it pinched between the tire and fender. Use the awning rod instead. They are easier to replace.

My normal procedure is to start the engine and hit the "store" button on the jacks. That will raise the jacks and allow the air bags to pump up, raising the coach. Then, go get your awning rod and by the time the bags are full you can reach in with the rod and pull the lanyards.
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Old 09-23-2009, 08:24 PM   #6
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Draining the air from the tanks is part of maintaining the Air Brake system. There are a few checks to insure the system is working correctly. These should be done prior to a trip or anytime the the air brake system is worked on.

Start engine and build air up the air pressure until compressor governor cuts out. This will be evident when the pressure gage needles stop rising. Depress the service brake treadle slowly and then release. Observe that for each depression Of the brake treadle that the service air pressure decreases by observing the gage. Continue depressing and releasing the brake treadle until the governor cuts in and the air pressure begins to increase. When this occurs, the air pressure in the tank as read on the gage should not be less than 85 psi. Let the air pressure build up until the governor cuts out as indicated by a steady air pressure. The air pressure in the tank should not exceed 130 psi. These listed air pressures are federal standards and the actual cut out and cut in pressures may be different on your coach.
The static brake test will verify that the vehicle air system that is normally charged as you travel is not leaking If your coach is equipped with an automatic transmission ensure the coach is placed on a level location, and block a wheel to keep from rolling. Place the gear shift selector in neutral and turn the engine off. Observe the air pressure gage reading and release the parking brake. Do not touch the service brake treadle or any other component connected with the air system. The air pressure in the tanks should not decrease by more than 2 psi in one minute.
The applied brake test will verify that the vehicle air system that is normally charged as the service brakes are applied is not leaking.
Depress the service brake treadle and keep it fully depressed for the duration of this test. After the air pressure has stabilized, observe the pressure gage. The air loss should not exceed 3 psi in one (1) minute (tap gauge occasionally). Any movement of the service brake treadle will vent or pressurize the service brake chambers and consume air pressure, causing the failure of this test.
The low air warning device test will verify that the low air pressure alarm goes off as designed. Turn the ignition on (key switch) but do not start the engine. Observe the air pressure gauge and pump the service
brake treadle until you can see the low air pressure warning light come on and/or hear the warning buzzer. The low air pressure warning should come on at about 60 psi.
The Emergency brake system test will verify that the vehicle emergency brake system functions as designed.
Turn off the ignition and then reduce the air pressure by depressing and releasing the service brake treadle until
the emergency (parking) brake handle pops up. By observing the pressure gage this should occur when the tank pressure falls below 45 psi.
Start the engine and immediately place the transmission in gear and GENTLY try to move coach slowly against the emergency brake with low air pressure. At this pressure the emergency brakes should be applied by the large springs in the rear brake chambers. As soon as the engine is started the air pressure will start to build up but it will not be routed to the emergency brake chamber because the handle has popped out. Caution should be used so as not to apply too much pressure against the brakes and drive train.

The emergency brake test will verify that the vehicle emergency brakes can be applied, as the vehicle is moving. When applying the emergency brakes on a moving coach, the vehicle speed should not exceed 5 to 7 mph. (I do this with the coach barely moving)
Allow the air pressure to build up until it cuts out. Put the coach in gear, release the parking brake and allow the coach to move forward slowly. Apply the emergency (parking) brake by pulling up on the button. Do not operate the service brake treadle. The vehicle should come to a complete and sudden stop.
CHECK SERVICE BRAKES (verify that the service brakes are adjusted so they do not cause a pull in either
Set coach in motion and apply the service brake firmly to see if the steering wheel pulls to the left or right.

Hope this helps...
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Old 09-25-2009, 05:10 AM   #7
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This needs to be added to the library, if it's not already there.
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Old 09-25-2009, 06:52 AM   #8
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I believe most modern air braked MH's have automatic moisture ejectors.

I have never had any moisture drain by pulling the lanyards.
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Old 09-25-2009, 08:44 AM   #9
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air brakes

thanks to all. i have a very good overview now.

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