[Ronald]

[Archived]

I had a similiar noise last fall while hooked to shop air in the garage. After I rebuilt the air dryer, it stopped. I never did really figure out where it was coming from, but it sounded just like you described. If I unhooked the shop air, the sound would end.

I suspect the noise was air escaping from the wet tank through the dryer.

[Davy]

Greg,

If the noise is coming from between the two rear axles it might be the three port Norgren valve that is to either keep the air path between the tag and drive axle air bags open (normal position) or closes between the two sets of air bags and exhausts air from the tag air bag. Try cycling the tag lift to see if that stops the noise.

There is a lot going on in that area on our air systems and there are othere valves, the air dryer, and the rear auxiliary air distribution which is fed from the front of the coach (might not be on your coach) so you may have to wait until you can get under the coach before you can isolate the origin of the noise. You know about safety so be careful if you get under there.

[Larry & Diane]

Greg,

If your aux air compressor is cycling often, once per hour or more, then you are leaking excess air (A “tight coach” aux air compressor cycle for me is once a week). The noise could be related to air escaping.

If your aux air compressor is not cycling often, then here is another idea. On my coach when I dump all the air and set the coach all the way down, I will hear “groans” in a sort of timed sequence for a few minutes after I dump the air. I diagnosed this to the rubber mounts on the drag links connected to the rear axle. The rubber is dry and will make this noise when the dropped coach causes the drag link/bushing to move to this extreme.

When my coach was leaking aux air and the tag axle would dump, I would hear this same noise as the coach settled. For owners with newer coaches that do not deal with a tag axle dump on low aux air, this issue would never happen.

Let me know what you find on this. Knowledge is a powerful thing is dealing with these older coaches.

Hector

[Rodger]

When I first got my coach, mine did not make this same noise but I had a very leaky coach, especially the front norgren between the front tires. I replaced it with a new one, the leaking air stopped but this “fog horn” noise started. On mine, after the coach airs up to travel position, everything is fine until I shut the coach off after the trip. Immedicately after shutting down, mine starts to “sing like a fog horn”. The horn blasts last about 5 sec and occur every 20 sec until the coach loses enough air to settle onto the stops. Once on the stops, no more “fog horn” noise. I have noticed, purely by accident, if I am inside the coach and walk around, as I shift the coach weight around the noise will stop and start. I would really like to know what is causing this as it is embarassing pulling into a campground and having the coach “sing” for several hours if I decide not to dump the air and level the coach since I have hydralic levelers rather than air.

Rob

91 XL40

Missouri

[JIM]

Rob,

There is nobody on this planet that can tell you where your coach is leaking air. What every one of us can tell you is that we are all affectedf by air leaks and the only way to attain a coach with an air leak rate that is acceptable to you is to start chasing leaks. I can tell you from chasing leaks for 22 years is I use a tiered process starting with the obvious and working my way up the ladder to identify the most difficult.

Ears……..I use mine as the first attempt to find leaks. When you can hear the leak, it is big and worth fixing.

Soapy water……This is the next step for me. Keep in mind I do not use a scatter gun approach as I get into leak detection but analyze the leak location based on my understanding of the pneumatic system, For example if it keep leaning to the right, I will focus exclusively on the valves and connections associated with the 2 drive and single tag axle air bags on the right rear.

Stethoscope…….This is a good way to “hear” leaks you may not hear with your ears. Again, this is specific to a particular leak and location.

Ultrasonic leak detector……..The benfit to this is is helps me locate leaks internal to valves or at fittings that are otherwise difficult or imposible to detect except for using a bubbler.

Bubbler……..This is a device Hector has shown us and when all else fails hook a bubbler in specific air lines and if the leak is downstream you will see the leak in the form of bubbles in a sight glass (bowl). Leak free means no bubbles. Unlike other methods, when you use the bubbler you are progressively connecting it in line working your way upstream or downstream to isolate leaks. This is the absolute in leak detection, but when you get to this point you have to have a lot of patience and a willingness to check for leaks from connection to connection.

Bottom line, leak detection and repair is important and letting a coach accumulate countless small leaks is a sure way to drive an owner nuts at some point. If your coach settles down in the front that particular leak or series of leaks is isolated to the air bags or connections or Norgren valves associated with the front suspension. It may be the ride height valve for the front is leaking, but when the key is off with a level low system it is not part of the problem you describe.

[Greg]

Greg, I heard your described sound, in the shop, after I changed all my brake chambers and hoses. To perform the task all air was remved from the systems. This air down condition was for a period of about one week. After completion of the task, the system was aired up through the rear fill valve with shop air. This filling took up some time until the entire system was filled and what I will call in balance. There were many moans and groans and fog horn sounds until the air reached all components, tanks and check valves and was in balance. I can not definitavely point to any one thing that made the sound, it was scarry and disconserting at first, for I thought I had done something wrong. Not to worry though after a couple days of sitting there on the stands connected to shop air everything stabalized and has been quiet since. I even bought a new brake tredel valve as that had air pouring out of it which is an indication of failure. Did not end up using the valve as it too stabalized and since has shown no signs of leakage.

I think the majority of sounds come from check valves in the system between tanks and components.

JIM

[JIM]

Greg,

What Jim describes is what we all will hear when refilling an air depleted coach using shop air. The noises are associated with all sorts of valves working independently or in concert as the air from the fill point Jim describes works its way through the system and has to satisfy a variety of protection valves before progressing onto the next portion of the system. If the coach is trying to raise up as well (or at least have the air bags pressurized) there will be even more noises as various tanks and air bags are filled and bushings in the suspension go from relaxed to loaded.

But If I understand your post, the only air system being satisfied is the aux air unless your coach enables aux air to back feed into the primary and secondary air system, in which case it is traveling in the wrong direction through protection valves which might attribute to the noise. Without having a set of ears able to focus on the origin, any one of us is just guessing. Keep in mind that when parked there is no air beyond the air tanks and relay valves to your brake chambers, so at least you can rule them out. FWIW Hector and I had a question amongst each other regarding if aux air would fill the brake systems. Apparently on his coach (and maybe others) that is possible, but on my two coaches which were produced on either side of his coach vintage I could not get aux air into the brake systems. When that happens I suspect an issue with protection valves, which really should be checked periodically because of their important contribution to our safety.

[Darrell]

Greg,

Did you see the post on the other site by Coach Pro? He pointed to the dryer as I did here.

[Jerry]

I noticed that my batteries were down (21.8v) and the coach would not start. My aux air is the culpruit for draining my batteries, so I have not turned it on again. The noise is louder on the Passenger side than on the Drivers side. I am wondering if I am somehow pushing air into the dryer. My fog horn in not loud enough for anyone else in the park to hear. I have replace all the Norgren valves (not that mean they are leak free) except the one forward of the Passenger drives. My Aux compressor runs about three times a day. So I don’t think it really major, I have it on to keep my system from dumping the tags. When I get home and can get under the coach with supports I’ll let you know what I find. Thanks for everyones input on this.

[Ace]

Is this aux compressor something you added and plumbed to the rear or front air access point? For what it’s worth, when I hooked shop air to the front access going direct to the aux tank, it didn’t get the moaning noise. Then when shop air was hooked to the rear access point, the moaning and honking would happen. All went away after I rebuilt the dryer.

[Archived]

Tom I added it and plumbed it into the Front Aux tank with a check valve. I get the same groans and moans from the rear with shop air. It kind like an old man getting up off his knees.