My 2003 international 300 sounds like it’s breathing?

[Pandaberrylime]

So I’m posting this here because it sounds like the breathing sound is coming from the bendix. I’ve read a lot of threads saying it’s probably the turbo, but there is no change in the way the bus has been running, such as the 2000 rpm issue and there’s been no loss of power. Our bus does not have air breaks and the only things that run on air are the air bag suspensions, the air ride seat, and the door (which we’ve disengaged currently). It only does it after an initial acceleration, or after the pressure gauge has filled up. The psi runs normally but seems to purge itself and then refill about every five seconds. I’ve found the place it looks like the sound is coming from, but I’m not completely sure. It’s very loud, and sounds like someone breathing on a respirator. The part is attached. Is there anybody else that has had this issue?

[Taz420]

The air system has a compressor, as well as a "governor". Since the air compressor isn't "cycled" with an electromagnetic clutch like the compressor in an AC system is, the governor is what maintains the tank pressure within operating range (usually cuts in at 90psi and cuts out around 125). When it cuts out (tank full), it is still compressing air that has to go somewhere. That's what the unloader tube is for - it just vents the compressor output to outside, and it will sound like a constant hiss.



However - it should NOT be cutting in and out/cycling that fast. So you either have a pretty sizeable plumbing leak (other than the leaky seat, because that's not going to bleed 40psi in a few seconds), or the governor has failed and its not sealing off properly when it cuts out.


Is the pressure gauge swinging wildly while this is happening? You said the air door is disconnected, if you removed the solenoid, did you cap the line?


My guess would be the governor. For one I had that happen on one of my buses at work, and I think a leak that big would be very easily noticeable.

[sportyrick]

If you don't have air brakes and not the usual engine driven air compressor but a few things run on air where is the air coming from? Sometimes they have a small electric motor driven compressor to run accessories. It sounds like a leak to me and you can't hear it?

[Taz420]

Originally Posted by sportyrick

If you don't have air brakes and not the usual engine driven air compressor but a few things run on air where is the air coming from? Sometimes they have a small electric motor driven compressor to run accessories. It sounds like a leak to me and you can't hear it?

The air door is high pressure/low volume, air suspension is medium pressure/high volume and an air horn (which is an available factory option) is high pressure/high volume. It wouldnt use an electric compressor because an electric HV/HP compressor would need an insane amount of current at 12 volts to run. It would still have the same compressor/governor system that an air brake bus would have, except it would only have one tank (no need for the primary/secondary redundant split system).

If it is a diesel it most likely would have the standard gear driven compressor on the driver's side. However he mentions the sound coming "from the Bendix", which to me says he has the front mount belt-drive Bendix compressor (possibly a gasser?), which has the governor mounted right on top, and no unloader hose... So the sound would come right from the assembly itself.