Leaking Air When Pressing Brake Pedal

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Pro_LeadFoot_Operator, Jan 23, 2023.

  1. Pro_LeadFoot_Operator

    Pro_LeadFoot_Operator Bobtail Member

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    May 29, 2017
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    Hey how's it going everyone, firstly I want to thank everyone for their contributions to this forum be it questions or answers because I have referred to this site for many problems and often have been able to find a solution or the very least have found guidance in the right direction.

    So my issue is in my 2016 KW W900, if I have my service lines hooked up (red,blue,green) but not connected to a trailer i.e. example just bobtail (tractor only), when I apply the brake pedal I get a massive exhaust leak from both the blue service line and the exhaust port in the engine bay from the firewall. Now if I unhook my service lines (red,blue green) and I apply the brake pedal the problem is nonexistent. What needs to be replaced?
     
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  3. Animosus

    Animosus Medium Load Member

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    SE Wyoming
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    What do you mean hooked up but not connected to a trailer? What are they hooked up too.
     
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  4. Pro_LeadFoot_Operator

    Pro_LeadFoot_Operator Bobtail Member

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    May 29, 2017
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    When my service lines ( red, blue, green ) are connected to my tractor , they are quick connect fittings, I believe they are referred to as delivery ports? For example, I arrive at a delivery location and disconnect and unhook from the trailer, the glad hands that connect to the trailer I keep secure with bungie's to the catwalk behind my sleeper, the 3 service lines are physically connected to my tractor , if I apply the foot brake I can hear air coming out of the blue service line, also if I apply the trailer brake with the hand valve air leaks through the blue service line. Now if I disconnect from my tractor I do not leak air when applying brakes.
     
  5. Dino soar

    Dino soar Road Train Member

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    Still having a little bit of a hard time understanding exactly what you mean. I'm assuming when you say red blue and green you mean red for emergency blue for service and green for electric.

    Your tractor brakes release with the push button valve but you do not push the button for the trailer if you are Bobtailing.

    At that point nothing comes out of your airlines that go to the trailer.

    When you push the brake button for the trailer, that allows air to go through the emergency line and when you put your foot on the brake now air will go out the service line.

    If it is not working like that then you are having a problem.
     
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  6. D.Tibbitt

    D.Tibbitt Road Train Member

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    Gettin' down westbound
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    when bobtailing do you have the red brake knob pushed in?
     
  7. Goodysnap

    Goodysnap Road Train Member

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    If air is leaking from the blue trailer service line without the red knob in, the tractor protection valve is stuck open. Replacing the valve will fix your issue.
     
  8. 201

    201 Road Train Member

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    high plains colorado
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    Most trucks have a "fake" connection on the back, that you connect the lines to, like a trailer, but don't go anywhere. If you just lay the lines on the catwalk, dirt and moisture can enter, plus, I think it's illegal to have them laying on the deck plate. That would stop the leak, but I agree, something in the foot valve is kaput or froze..
     
  9. Pro_LeadFoot_Operator

    Pro_LeadFoot_Operator Bobtail Member

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    May 29, 2017
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    The air is leaking from the blue service line gland hands and exhaust port on the firewall when I press the foot brake or pull the trailer brake hand valve, the red valve is out, not connected to a trailer, yellow valve can be pressed in or it can be out, air will still Leake from the gladhand and firewall. If I disconnect my lines from my truck then it will no longer leak air when I press the foot brake or pull the trailer handbrake lever.

    Sorry for my lack of vocabulary but I thank you for trying to help.

    What could it be?
     
    Dino soar Thanks this.
  10. Pro_LeadFoot_Operator

    Pro_LeadFoot_Operator Bobtail Member

    7
    1
    May 29, 2017
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    No sir, whenever I am bobtailing the red valve is out.
     
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