Hissing from airbag — guessing this isn't normal lol

[skytripping]

Heard a hissing coming from the passenger-side front tire well after shutting down the engine last week. Here's what I saw/heard:

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

Bus takes about 10 minutes for the low-air buzzer/light to disengage, and that's only if I increase RPMs a tad for a few minutes. Is this something that can be repaired? Is a replacement required?

Thanks,

Ron

[Stormcloud]

Time for a dish-soap/warm water spray to see exactly where the air is coming from.
....and yes, it is not normal.

Mark

[skytripping]

Thanks Mark. Not sure if you could see it in the video (last bit), but it appears that the bottom lip of the top half of the airbag is dislodged, and I believe the bottom lip on the bottom half also appears to be unseated. But I don't know enough about these to really know what to look for or how to fix it once I find it.

[chessie4905]

Does it inflate properly when coach is aired up? If so, may just look that way when down. Has it ever inflated properly? Use soapy water spray or mechanic's stethoscope with the metal tip removed to verify it is leaking around air bag and not the air beam it is attached to or leveling valve or air lines to it. Air beam is the coach structure that top part of air bag is attached to. They have been known, pretty common actually, to develop pin holes from salt corrosion over the years and leak. The fix is to install block off plate on top air bag mount to correct it. Luke carries or can get the parts you will need if the bag is the culprit. It is not recommended to install block off plate on one side only, as the air beam provides added air volume and better expansion/compression characteristics to the system. By doing one side only, the coach will act like a car with one firm and one soft shock absorber.

[Scott & Heather]

Not enough info here. We need to know this:

1. Does that airbag ever inflate? If it doesn't then it might be unseated but that's somewhat rare
2. Have you physically gotten under there to move your hand around and actually find the source of the air leak?
3. When you're airing up, do you use fast idle? If not, then it's normal for it to take a long time to air up. Most old coaches need fast idle turned on or you manually holding the throttle to raise RPM's to get it it air up at a decent rate.


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[luvrbus]

Are those plated ? it looks out of place big time

[skytripping]

Thanks everyone! Great questions. I'll try to get under there today to inspect further and answer some of the questions you've asked.

[bevans6]

Very common to hear air sounds for a few minutes after shutting down - it can be as simple as the suspension was a little high and is being exhausted down to it's set point.  As far as time to turn off the low air alarm, 10 minutes from a cold start can be quite normal.  The test is called compressor recovery.  To do the test, follow these steps.

Air the bus up to full pressure - 120 psi, the air dryer purge valve will exhaust.  Let it set at full pressure until the suspension is completely full and the pressure gauge is not moving.

Engine off

Time test - observe the pressure gauge with brakes off for 1 minute - should be no observable pressure loss.

Time test - apply the brakes and hold them.  Observe the pressure gauge for 1 minute - should be less than 3 psi loss after the initial loss from applying the brakes.

Engine on again, fan the brakes until the pressure reaches 80 psi on the gauge.  Measure the time taken for the pressure to build from 85 psi to 100 psi.  Should take less than 30 seconds or so.

Brian

[skytripping]

I ran bevans6's suggested tests and made a video showing the 4 airbags up front when the bus is at 120psi. It took around 14 minutes from 60psi (where it was at when I fired up the engine) to 110psi with fast idle turned on. 5 more minutes to 120psi with fast idle off and revs up via the accelerator pedal. 9 more minutes running and pressure drops by 5psi. You can watch the video here:

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

I didn't have a chance to definitively isolate the source of the leak today (i.e. soapy water solution), but it seemed the sound of the hissing was easily augmented when I prodded the misshapen top airbag on the passenger side front set. I figured I'd upload the video I captured today to see what I could check off the list. I'll tackle whatever the next most practical steps are next, per your suggestions.

Thanks!

Ron

[skytripping]

Oops. Link was incorrect. Updated with the correct link. Sorry!!

[Scott & Heather]

Ron, it doesn't look like your air bags are even inflating. They should have much more air in them than that. They should look like this:



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[Scott & Heather]

Passenger front back is seriously wonky too. Where are you located Ron?


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[skytripping]

Ron, it doesn't look like your air bags are even inflating. They should have much more air in them than that. They should look like this:


Passenger front back is seriously wonky too. Where are you located Ron?

Thanks Scott. That's what I was guessing. I don't know much about how these air systems work in specific detail, but it would seem that if one or more airbags are leaking large amounts of air, the rest of the system will suffer. I see lower than expected performance in the rear as well, though none of those airbags seem to be more or less completely un-inflated like the front passenger side airbag (last of 4 in the video). Perhaps it's a leak in the air beam as has been suggested, but based on the fact that that one airbag is so off-kilter and that's where a massive flow of air is coming from, I would assume that's the obvious place to begin troubleshooting.

Please let me know if that's off base. Again, I'm going off of gut since I know very little about the specific mechanics of how these systems operate. If there's something I should be attempting to get that airbag re-seated/re-inflating (assuming that's the logical next step), I'd be very grateful for any suggestions/guidance you can give.

Ron

P.S. I'm in Northern Utah

[gumpy]

Find out where exactly that air is coming from. It's enough that you will be able to feel it if you get your hand in there. You should probably jack it up and block it. Remove the wheel if you have the means to do so. Ultimately, you're going to have to do that to fix the problem.

You either have a hole (crack) in the front passenger air bag, or the air beam has a hole in it.

As far as how they work:  The front and rear bags on the front axle are tied together with the air beam. The two sides are separate (i.e. they have two separate air beams, with two bags on each, Left and Right). The drive axle is set up similarly. Main difference is the drive axle uses larger air bags, and has a leveling valve on each side, whereas the steer axle only has a single leveling valve which fill both side air beams.

You have a major hole somewhere. Either in the front passenger air bag, probably in the upper lobe, or in the passenger side air beam.

BTW, here's a page with a bit of detail on replacing the front airbags: http://www.gumpydog.com/Bus/MC9_WIP/Mechanical/Steer_Axle/steer_axle.htm

[gumpy]

BTW, you might want to consider putting you location and bus model in your profile so the rest of us have a better idea what we're dealing with when you have a question.