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Discussion Starter · #1 · (Edited)
Have an IHC S1900 gas that won't hold pressure in the system very long when shut off. Every 5 minutes I hear a squawk in the air tank. I cannot find anything leaking but has to be. I changed the quick release valve above the front axle, afterwards the system wont hold pressure. Any thing I should check? Did the bubble test on everything I could see but the squawking has me baffled.
 

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The "squawk" you refer to, is the check valve functioning between the wet/primary tank/s and the secondary system. The air pressure is equalizing between the two systems. Your leak is therefore in the secondary system.

As for where the leak is...well if it is as big as you imply, I find it hard to understand that you can't find it. On an older truck I would first check the treadle valve and then the air tanks themselves. The air is going somewhere, and it makes noise when it does. If you need to, connect the wet tank to a shop air supply so it keeps things fully charged, will be easier to hear the leak.

The only time the quick release valves see air is when the brakes are applied. Instead of making the air return thru the treadle, they open and dump the application pressure and allow the brakes to release quicker. If you are losing air under normal circumstances thru a quick release, you have treadle valve and other issues.

The attached chart is one most commonly referred to in the industry. If you have a straight truck, then ignore the plumbing that make up the tractor package.
 

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There is also the possibility if the truck is plumbed with the fabric covered wire braid hoses, that you have numerous hoses resembling swiss cheese. That is about the only way you could have a major leak and not able to locate it....because it is actually thousands of little ones. Those hoses do break down and rot over time and that is a common failure;)

I have no idea of what your truck looks like...all I or anyone else can do is guess....
 

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This may not be of much help as we also have an S1900 although the DT466 diesel and I've not experienced anything like what you have been experiencing so far. What I have had happen and I think twice now is a brass 90 elbow within the solid steel ( or is that copper ) line off the air compressor, its cracked and then the compressor is running trying to pump up the system and unable to. The air lines Albertabuck mentioned, those can sure be a problem when they get older as the steel braid corrodes and yet the line from the outside can look fine if the cloth braid isn't damaged as I've had them snap in half on another truck that had them. Here's an idea that AB's swiss cheese comment triggered but I've not tried myself but sure should work if you can't find the leak and trying to eliminate hoses from being the culprit. Take dishwashing liquid and mix it with water in a spray bottle and douse the air lines while under pressure as that should get some action going, as well on the maxi pots when they are released ( chalk the wheels when messing with the brakes like that ). Had you tried having the maxi's applied to see how long the air leaks down, then reair and try again to see how long the air takes to leak down with the maxi's not applied, its sort of a simple test to see if the hoses or brake pots are leaking on the spring brake side. Don't forget to crawl around by the transmission to listen for air leaking there as well and in the cab at the selector ( assuming you have a 13 speed for instance )
 

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If you have been farming long you probably can't hear worth a darn. Get someone under 20 to help you.

Your leak could well be in the dash. There is the valve for the parking brake, and on larger trucks at least, air is used to move all the doors for the climate control system.
 

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Discussion Starter · #7 ·
If you have been farming long you probably can't hear worth a darn. Get someone under 20 to help you.

Your leak could well be in the dash. There is the valve for the parking brake, and on larger trucks at least, air is used to move all the doors for the climate control system.
But I have my hearing aids turned up on high! :( unfortunately I'm not joking.

Thanks for all the input and the primer on brakes, I have to admit I don't know alot about them since its the first air brake equipped truck I have had. You all have given me a direction to go.

The Combine Forum posters are just awesome!
 

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But I have my hearing aids turned up on high! :( unfortunately I'm not joking.

Thanks for all the input and the primer on brakes, I have to admit I don't know alot about them since its the first air brake equipped truck I have had. You all have given me a direction to go.

The Combine Forum posters are just awesome!

High frequency hearing loss. God's gift to the married man.


Believe me, I wasn't joking. I need the aids also, just to **** tight to buy them.

Air leaks are ultrasonic, we just hear them after the air slows down a little. Your hearing aids are probably set to tune out high frequency sounds, so that basically makes you a blind man searching for a light switch. Otherwise, there are ultrasonic detectors that are made just for finding leaks.
 

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I was being kind before and didn't bring up the hearing problem possibility as I know too, my hearing isn't what it used to be and that's half my lifetime ago when I had a hearing test done and was asked if I was around noisy equipment and when I said I farmed .... uhhhh, she goes. So yes, find someone young who hasn't had ipod buds stuck into their ears or other loud noises as I bet they will find the offending leak/leaks as long as there is no outside noise, vehicles, wind and so on.
 

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Everything except don't do that, and clean your room.
:D

I bought a good stereo back when country music was worth listening to (R.I.P., Waylon) along with a test record with a 20 MHz - 20 Hz sweep. That is, the record starts playing a tone at 20 MHz (20,000 Hz) which is considered the highest frequency humans can hear and slowly drops the tone to 20 Hz which is the low end.

I couldn't hear anything until the tone dropped to 10,000 Hz. We tried the sweep on a neighbour's stereo too. I couldn't hear anything until 10,000 Hz, but he could hear it briefly at 14,000 HZ. His wife and pre-teen daughter walked in so we played it again. Mother thought it was much too loud at 14,000 Hz and daughter had her fingers in her ears. We never did swap components around to pinpoint the problem
 
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