Air System Failure - Still Researching But Could Use Help

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Air System Failure - Still Researching But Could Use Help

November 29, 2017, 11:25:58 pm

After my trip to get the door open to be able to get out of coach, on way to storage the "ringer" for alarms or turn signals started dinging twice as hard when I was turning left. I released the turn signal but "dinging" continued and I saw HWH Travel Air Pressure Lost indicator. Looked at my gauges and pressure was slowly (but visibly) dropping. I was about three blocks from storage so continued there. Pressure continued dropping and I saw no pause in rate of decline. While I was backing into storage, pressure got so low (35-40 psi?) that parking brake knob kicked out. Rather than blocking door to enclosed storage, I pushed brake back in and drove 100 feet to outside storage site, got out and walked around FT but heard NO air leaking. Recent inspection at shop during other work said air bags are showing wear and should be replaced soon - next 6 to 12 months, or so.

Still doing research through Forum archives but will need to have things to check when (and if) I can get a mechanic to come out to diagnose/fix problem. (My mechanical skills are non-existent for automotive/RV equipment systems even though I am a Mechanical Engineer/Project Manager with a construction background, so if you need a petrochemical plant built in your backyard, call me.) However, I could really use advice on most likely items to check. I think failure of governor valves and/or air dryer would be first on list. Is this logical and any other items - semi-fast air loss, no sound of air hissing (by time I was able to check)

Re: Air System Failure - Still Researching But Could Use Help

Reply #1 – November 29, 2017, 11:45:37 pm

Think you are on the right track, if pressure falling and not building up again, and no sound of leaks, would suspect d2 valve first and them possibly air dryer, would do a percussion test on governor first. It is strange you could push brake button back in, because once pressure falls that low, it will apply spring brakes, and not release the them until pressure increases enough. But if brakes are worn or misadjusted, engine could override them.
At 30-40 psi, you would probably need to get real close to leak, to hear it.

Re: Air System Failure - Still Researching But Could Use Help

Reply #2 – November 30, 2017, 12:00:57 am

The pressure was probably too low to hear the leak. You might have to hook an air compressor up with the engine off to find the leak. Did you hold the air valve in to move back out? I know there is a 20 psi or so under the parking brake release that I can hold the release valve in and move while building up enough pressure to hold it in on my crane. It has the common D-2 regulator. Usually a D-2 failure doesn't leak, just over pressurizes or doesn't make air.

Re: Air System Failure - Still Researching But Could Use Help

Reply #3 – November 30, 2017, 01:14:03 am

Yes, Craneman. Trying to get coach out of way, brakes would let me back up so getting into storage was out of question but I was able to push knob for the minute or two that it took for me to get to a safe and out of way parking. Problem is that I have to get resolved/fixed before temp falls below freezing or go through process of winterizing coach with aquahot which is one of main reasons I have always stored in heated enclosed storage facility.

Re: Air System Failure - Still Researching But Could Use Help

Reply #4 – November 30, 2017, 01:43:33 am

If your losing air fast enough to see it on the gauge you have a serious leak. Which actually is a good thing. Should be a lot easier to find. Any chance you ran over something and it got up in the front air lines? Lots of lines up there exposed. Might want to crawl under the front end and have a look around and see if anything obvious. After that you are going to have to build air. Does your coach have an auxiliary compressor? If so fire it up and see what happens. The major components of an air system rarely just fail outright and even if they did would not leak out like that. Gut feeling is a broken fitting or line somewhere and I would start with the leveling system. Brake systems built pretty tough and though I have had my share of air leaks, brakes never the culprit.

Re: Air System Failure - Still Researching But Could Use Help

Reply #5 – November 30, 2017, 08:59:04 am

Agree with the above advice. If you can get a suitable air compressor to where your coach is parked, you could first try to pressurize the coach air system using the compressor. This is usually done by connecting the compressor air hose to the "tire fill" hose on your coach. This requires a "double male" air hose quick connect fitting. (see photo) If you can get the coach air system pressurized using a external compressor, and it holds pressure, then you have ruled out the possibility of a massive air leak on the coach.

If no obvious air leak is found, then I agree with Jim C. First place to look is the D2 governor. Here's why. You're driving along and everything is working fine, then suddenly your air pressure starts to fall for some unknown reason. First thing that should happen is your engine air compressor kicks in and tries to maintain air pressure. Our big air compressors can compensate for some pretty substantial air leaks and keep you moving, although they may have to run continuously. But in this case that (apparently) did not happen - your compressor did not kick in. So what is the device that tells the air compressor to kick in? The D2 governor.

The D2 has a internal sliding piston. When your air compressor is in the "unloaded" mode (not compressing), the sliding piston in the D2 is pushed (by system air pressure) against a strong spring. As system air pressure drops to "cut-in" pressure, the spring will force the piston down to the point where D2 sends a signal to the air compressor to start compressing. If the D2 piston is stuck in the "unload" position, the compressor will not start compressing, and system air pressure continues to fall.

So first priority is to rule out a massive leak. Then start engine, see if air pressure holds (or builds). If air pressure holds, "fan" the brake pedal to reduce air pressure to "cut-in" point, and see if the engine air compressor kicks in and operates normally. If the air compressor does not kick in, you could try tapping the D2 (lightly) with a hammer to see if it frees up. Or, just replace the D2. They are cheap, and available at most NAPA or auto/truck parts stores.

Haldex D2 Governor Service Data

Re: Air System Failure - Still Researching But Could Use Help

Reply #6 – November 30, 2017, 09:45:14 am

D2 Governor is the low hanging fruit when it comes to failure to build air. When we got sidelined by side of the road due to air loss out in the middle of nowhere in Canada, it was the first thing I tried to remedy the situation. Unfortunately, it wasn't the problem. The air dryer was purging air constantly. Even when standing close enough at the back with the engine running, it was difficult to hear. I only knew for sure where the air was coming from when I put my hand below the purge valve at the bottom of the air dryer and could fell the air rushing out. The coach couldn't build more than about 30psi. I had to cobble together an air dryer bypass out of parts from the air dryer and a ½ plumbing T that I happened to have. The forum was there for me to give me the info I needed to know how to bypass the air dryer and get us down the road (with frequent tank draining!). Since then, there have been a number of threads about putting together a 'kit' to make by passing the air dryer doable by the side of the road. Chuck did an excellent write up on it. If you can feel the air puking out the purge valve with your hand while the engine is running, you might try first a percussive adjustment to get the check valve to seal and if that doesn't work, the by pass will get you moved to a better place. Or buy a remanufactured unit from a good source such as NAPA and replace it which you will probably need to do anyway. You could also rebuild the air dryer, but the two kits necessary to do a complete job aren't that much less than a re-man. unit.
Don

Re: Air System Failure - Still Researching But Could Use Help

Reply #7 – November 30, 2017, 09:46:28 am

Chock wheels so coach cannot roll start engine and see if you build air pressure. If you do shut off engine and release parking brake. Get out and listen for a air leak. If it dropped rapidly it might be a bad diagram on a rear brake chamber. The chamber uses air to release the brake hence why it built up pressure when parking brake was applied.

Re: Air System Failure - Still Researching But Could Use Help

Reply #8 – November 30, 2017, 10:07:26 am

You may also want to check the petcocks on you air tanks. I have had a stone jump up and hit the petcock and loosen it enough to have the same issue while driving.
John

Re: Air System Failure - Still Researching But Could Use Help

Reply #9 – November 30, 2017, 10:42:19 am

One thing that should be obvious to everyone reading this thread: CARRY A SPARE D2. Should be one in the spare parts drawer of every coach. They are cheap, don't take up much room...but might save you a lot of time, trouble and grief. "Don't leave home without it!"

Re: Air System Failure - Still Researching But Could Use Help

Reply #10 – November 30, 2017, 11:48:23 am

Agree with Chuck & Chuck.

Hook up a portable 120v air compressor via the adaptor Chuck mentions. If it builds air you probably don't have an air line leak. You can place the air compressor in one of the bays (if you have one with a 120v outlet), run the air hose from the air line bay over to the bay with the compressor in it, and start the generator to keep the compressor running. Now start up the coach and move into storage. You now have lots of time to troubleshoot and fix.

If it doesn't build air pressure let the compressor run and build as much air as it can then shut it off and listen for leaks.

Lots of good advice here. Good Luck!

see ya
ken

Re: Air System Failure - Still Researching But Could Use Help

Reply #11 – November 30, 2017, 12:48:00 pm

I air up my system as Chuck described with a double ended male air fitting. But add in an in-line air dryer/water separator to keep moisture out.

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Re: Air System Failure - Still Researching But Could Use Help

Reply #12 – November 30, 2017, 01:31:14 pm

There is a pop-off valve ( pressure relief ) on the wet tank ( at least on mine there was ), when I ran over something and broke it off I was dead in the water. A mobile mechanic had a 3/8 pipe plug which he put in and I drove to a truck stop where it was replaced. Leak from this will be very apparent.
Gary B

Re: Air System Failure - Still Researching But Could Use Help

Reply #13 – November 30, 2017, 10:06:01 pm

When was the last time the air dryer was serviced?

If you don't know or it was longer than 2-3 years I'd replace it with a reman.
It's time whether you can immediately identify it as your problem or not.
I was looking at a schedule of rebuild kit, skip two years , replace with reman, skip two years, repeat.
Some say one year cycle.

Re: Air System Failure - Still Researching But Could Use Help

Reply #14 – December 01, 2017, 09:20:27 am

I am comfortable with a 3 year cycle-- replace with FACTORY, repeat FACTORY (as in the company that made it) reman. That way all valves and heater are new as well as filters. If you like, alternate with just replacing filters. But, if you are paying for labor, just go with factory reman.

Re: Air System Failure - Still Researching But Could Use Help

Reply #15 – December 04, 2017, 04:35:41 am

Fortunately, my air pressure failure occurred about three blocks from storage facility. Could not get inside heated storage but parked about 150 feet away outside. Replaced dryer and D2 valve. (Local truck stop gave me wrong Meritor governor - number was close but had flat mounting service in lieu of recessed, so when I took it back I got a Bendix governor that fit and matched the unmarked governor taken off.)

The Meritor had a Blue cap whereas the Bendix has a black cap. Truck stop sales said both had been preset.
When Bendix governor and dryer installed, cranked engine and pressure rose to 35 psi where it stayed steady. STRONG bleed to atmosphere through D2 exhaust precluded any higher pressure. With mobile mechanic's air compressor, we backfed through air hose connection (thanks, guys) until pressure reached 70 psi. (Not sure if we could have gotten higher gauge pressure with air blowing out D2 governor anyway but mechanic's friend (mentor) mentioned we should not exceed about 70 psi gauge anyway because concern that there may be a restriction/blockage in an air line causing gauge pressure to show only 70 psi while actual line pressure may be a lot higher. Anyway, with the rapidly falling 70 psi blowing through governor exhaust to atmosphere, we were able to drive it into heated storage and park the coach. (Took several "refills" to 70 psi from mobile mechanic's compressor (in tandem with on-board compressor.)

So, any suggestions? 1) Could the new Bendix NOT be factory set to release at 125 psi but releases at 35 psi instead? Don't know if release through stuck governor was original cause of pressure loss since I heard no air flow before we replaced governor, but the system will definitely not get above 35 psi while exhausting through Bendix air exhaust to atmosphere port.

Luckily, I did not need to winterize - temp below freezing two days later - but coach is now in heated storage and cannot go anywhere until this issue is resolved. Mobile mechanic - who was not very experienced - asked friend and he suggested all lines should be disconnected and blown out and friend had large air compressor tank on truck and available to help. Should I proceed with trying to blow out lines or does someone have a better suggestion - maybe replacing Bendix governor that is exhausting with correct Meritor - to try first? What else, other than a blocked line or governor set to wrong pressure could cause the strong exhaust to atmosphere through governor exhaust port? This exhaust will have to be corrected before any further resolution can be performed, if needed when exhaust loss is corrected.

Re: Air System Failure - Still Researching But Could Use Help

Reply #16 – December 04, 2017, 08:11:03 am

Hugh,

I'm not there, and long-distance diagnosis is always tricky. That being said, my first thought is that one of the bottom (supply) ports is still open. The air hose from your wet tank to the D2 is connected to one of the bottom ports on the D2. There are 3 "supply" ports on the bottom of the D2. The unused ports must be closed off with the supplied threaded plugs. If not, you would have a constant air leak as your have described. That is the only logical reason I can think of that would cause a continuous flow of air from the D2. Is the air leaking from one of the bottom ports?

There are also 3 "unloader" ports in the middle of the D2. Just like the supply ports, the unused unloader ports must be blocked or plugged to prevent air leaks. The threaded plugs are supplied for this purpose. Is the air leaking from one of the middle ports?

The exhaust port on the D2 is the top port (nearest the cap). There is only one exhaust port. Are you sure this is where the air is coming from? The only way a brand new D2 could suffer a constant leak from the exhaust port would be if it came out of the box with the internal piston stuck in the "UP" position against the strong compressed "pressure setting" spring. I can't imagine this happening.

The color of the cap on the D2 is not critical - they come with various style caps. There are only two kinds of D2: adjustable, and non-adjustable. If you remove the cap off the top of the D2, you can immediately see if it is adjustable. The adjustable model will have a shaft with a screwdriver slot in the top. The shaft is held in place by a locknut. NO D2 ever came from the factory set to "unload" the compressor at 35 psi, so you can rule out that possibility.

Hopefully there is a simple explanation for what your D2 is doing. Study the diagram on the first page of the manual linked below. The D2 is not all that complicated once you understand how it works.

BENDIX D-2 GOVERNOR MANUAL Pdf Download.

Re: Air System Failure - Still Researching But Could Use Help

Reply #17 – December 04, 2017, 08:52:46 am

One video is worth 1000 of my words.

https://www.youtube.com/watch?v=FHGcXvDmZ5E

Re: Air System Failure - Still Researching But Could Use Help

Reply #18 – December 04, 2017, 09:12:32 am

It may also be the actual unloader valve of the compressor. Some good tip advised me to oil the unloader port.
I had similar symtoms. But at around 65psi..
Remove the D2 , spray light oil into the unloader port/valve . Replace D2 .

Purchase spare D2 and unloader valve kit.

Re: Air System Failure - Still Researching But Could Use Help

Reply #19 – December 04, 2017, 11:40:01 pm

Quote from: John and Stacey – November 30, 2017, 10:07:26 am

You may also want to check the petcocks on you air tanks. I have had a stone jump up and hit the petcock and loosen it enough to have the same issue while driving.
John

Yup.... wet tank drain

Re: Air System Failure - Still Researching But Could Use Help

Reply #20 – December 05, 2017, 07:51:07 am

Had an air system problem a couple of months ago kinda like this. Caused by complete failure of a little pop off valve just under and forward of the curbside rear. Probably not what's going on here. Coach couldn't build any air pressure and came to rest on tires until replaced. Only found it when I pressured the system with an external compressor. Auxiliary compressor wasn't working and now chasing issues related to that.

Re: Air System Failure - Still Researching But Could Use Help

Reply #21 – December 05, 2017, 09:02:21 am

Quote from: Thedude – December 05, 2017, 07:51:07 am

Caused by complete failure of a little pop off valve just under and forward of the curbside rear.

That "pop off valve" is the safety relief valve on your wet tank. It protects your air system from over-pressure damage in the event of a uncontrolled air compressor event. It should be rated to open at 150 psi. If it ever does perform it's assigned function and open, you won't have any problem hearing it. It is LOUD! Been there, done that...

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