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Thread: Air leaking into air intake stack (parking brake NOT applied)

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    Default Air leaking into air intake stack (parking brake NOT applied)

    So I'm getting air leaking into the air intake stack but it's when the parking brake is released, not when the parking brake is applied (as indicated in the TM). This is causing the primary and secondary air systems to bleed down. When I activate the parking brake the leaking stops and air pressure in both systems builds right up to normal. I've replaced the treadle valve, with another unit from a working truck. Reading the TM the only other thing that it lists is the one-way check valve. I'm going to try and pull it off and take a look at it tomorrow. It's obviously hard to tell, when the truck is running, but it almost sounds like air is escaping somewhere near the parking brake. I've hooked shop air up but it wasn't much help tracking the issue down. Anyone else have a similar issue? Thanks.
    Last edited by dilligaf13; 11-16-2014 at 00:40.

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    The only thing I can suggest is to let the air pressure build completely, then then shut the truck down, then use a piece of long flexible air hose( I use 1/4") stick one end in your ear and use the other end to search for the leak. When you come across the leak you will definitely hear it.I hope this helps!

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    Scroll down and read some of te similar threads.
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    ONE of your SPRING BRAKE rubbers is leaking, what you here is air leaking into the vent system, the easiest way to find which pot is leaking is to remove the vent line from the pots, then see which POT is leaking air, DO NOT check the line because the939s use a common vent system.
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    I checked all the Service Brake Chamber's vent lines and there was no air leaking at any of them so their out as a cause.

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    Quote Originally Posted by dilligaf13 View Post
    I checked all the Service Brake Chamber's vent lines and there was no air leaking at any of them so their out as a cause.
    I did NOT say service brakes, I SAID " spring brake RUBBER", air holds the spring brake off, no air the spring brake sets. You HAVE a spring brake rubber leaking.
    Ron, AKA , FTF (FIVE TON FIXER), AKA KGR (kinder/gentler Ron)
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    vietnam-1/66-8/68
    "Technical Manuals are the path to Illumination...
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    RECOVERIES (to a point) WHERE EVER, 703-389-6705, 73m819@gmail.com
    73m819, tractor/wrecker AKA NO LONGER Wrecked Wrecker
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    Use CUCVs, a small step below BOBBERS as 5t wheel chocks
    GOD help the MV or LEGO world if I win the LOTTERY
    Long live BIG GREEN IRON

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    Gotcha. Nothing in the -23 TM about that, guess I'll have to do a little more research.

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    So I unhooked all the vent lines, from the four rear spring brake chambers and no air was leaking from any of the fittings. In the attached picture the bottom line is the supply and the others are vent lines, best I can tell from the TM pictures. I think that removes them as the causes of the air leaking into the intake stack.
    Attached Images Attached Images
    Last edited by dilligaf13; 11-17-2014 at 22:07.

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    Did you remove the vent lines with the spring brake set or released, In post number 1, you say that you lose air when the spring brakes are released, If you are SURE none of the pots are leaking, look at the quick release valve that is under the left cab step.
    When the spring brakes are set, do you still lose air if you apply the service brakes ??
    Ron, AKA , FTF (FIVE TON FIXER), AKA KGR (kinder/gentler Ron)
    Gainesville, Ga.
    vietnam-1/66-8/68
    "Technical Manuals are the path to Illumination...
    Download, Study Learn"---rlwm211
    POOR PLANNING or NOT READING TM on your part does NOT constitute a EMERGENCY on our part.
    RECOVERIES (to a point) WHERE EVER, 703-389-6705, 73m819@gmail.com
    73m819, tractor/wrecker AKA NO LONGER Wrecked Wrecker
    What ever else that can be drug home
    Neutered 6X6s (bobbers) = 10t wheel chocks
    Use CUCVs, a small step below BOBBERS as 5t wheel chocks
    GOD help the MV or LEGO world if I win the LOTTERY
    Long live BIG GREEN IRON

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    [QUOTE=73m819;1631275]Did you remove the vent lines with the spring brake set or released,
    I removed the vent lines with the spring brakes set, spring brake release control valve out for normal operation, and there were no leaks. I don't remember if I checked for leaks, from the vent lines, with the spring brake release control valve in.

    In post number 1, you say that you lose air when the spring brakes are released,
    I lose air, through the stack, when the parking brake is released.

    If you are SURE none of the pots are leaking, look at the quick release valve that is under the left cab step.
    Will do. Can the parking brake valve malfunctioning cause this issue? Nothing in the TM about it but.....

    When the spring brakes are set, do you still lose air if you apply the service brakes ??
    I'll have to triple check tonight, when I get home, but I'm 99% sure I remember that I don't lose air when I apply the service brakes. Thanks.
    Last edited by dilligaf13; 11-18-2014 at 12:03.

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