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Emergency line blows air

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Dino soar, Apr 10, 2023.

  1. Apr 10, 2023 #1
    Dino soar

    Dino soar Road Train Member

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    If I do not have any lines hooked up to the trailer and I release the tractor brakes, at that point if I put my foot on the service brake I have air coming out of the emergency line for the trailer.

    Any ideas?
     
    Dino soar, Apr 10, 2023
    Dino soar, Apr 10, 2023
    #1
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  3. Apr 10, 2023 #2
    kemosabi49

    kemosabi49 Trucker Forum STAFF Staff Member

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    Tractor protection valve
     
    kemosabi49, Apr 10, 2023
    kemosabi49, Apr 10, 2023
    #2
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  4. Apr 10, 2023 #3
    AModelCat

    AModelCat Road Train Member

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    If you mean service line, then tractor protection valve.

    If its coming out the emergency line I got nothing.
     
    AModelCat, Apr 10, 2023
    AModelCat, Apr 10, 2023
    #3
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  5. Apr 11, 2023 #4
    SmallPackage

    SmallPackage Road Train Member

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    Johnson bar valve may be bad or it’s exhaust may be plugged by springtime mud dauber. Maybe oiled up, dirty or bad seals. It could be internally bypassing back through the supply/emergency circuit. I know it Sounds unlikely but I did run into this scenario once and it had me scratching my head for days trying to troubleshoot it. Replacing the tractor protection valve, foot valve, or PP-1 valve didn't fix it. Luckily I had good used parts laying around so I didn’t spend money just changing parts to find it.
     
    SmallPackage, Apr 11, 2023
    SmallPackage, Apr 11, 2023
    #4
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  7. Apr 11, 2023 #5
    Lazer

    Lazer Road Train Member

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    Make sure the ‘johnny bar’ is all the way up.
     
    Lazer, Apr 11, 2023
    Lazer, Apr 11, 2023
    #5
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  8. Apr 11, 2023 #6
    mud23609

    mud23609 Medium Load Member

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    Your tractor protection valve has probably gone bad. Seen it a few times.
     
    mud23609, Apr 11, 2023
    mud23609, Apr 11, 2023
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  9. Apr 11, 2023 #7
    Dino soar

    Dino soar Road Train Member

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    I think I made a mistake. It was blowing out of the service line not the emergency line. I think I had the service line hooked on the left side of the holder and thought it was the emergency side.

    I tried it again and definitely with only the tractor brakes released and my foot is pressed on the tractor brakes I have air coming out of the service line for the trailer.

    I put a new mv3 valve in not that long ago and where I purchased it they're going to give me another one.

    Hopefully that will be one more problem solved.
     
    Dino soar, Apr 11, 2023
    Dino soar, Apr 11, 2023
    #7
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  10. Apr 11, 2023 #8
    Goodysnap

    Goodysnap Road Train Member

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    If service air comes out of the blue gladhand without the Trailer knob in… your tractor protection valve is stuck open.
     
    Goodysnap, Apr 11, 2023
    Goodysnap, Apr 11, 2023
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  11. Apr 11, 2023 #9
    WitchingHour

    WitchingHour Road Train Member

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    Tractor protection valve. Just had the same issue on an M2-112 dump truck and had to replace it. Emergency air, service air… all has to pass through the protection valve before those trailer air lines charge.
     
    WitchingHour, Apr 11, 2023
    WitchingHour, Apr 11, 2023
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