Question about tractor trailer system

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by JamesMc84, Jul 27, 2021.

  1. JamesMc84

    JamesMc84 Bobtail Member

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    Mar 20, 2017
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    I’m plumbing in a trailer brake air system on the international 4400 that’s never had wir brake towing capabilities.

    the supply side was easy to figure out. The service side I’m running into a issue. I was told I didn’t need to replace a the treadle valve by the dealership I got all the parts from but I’m kinda stumped on how I set up the service side so I don’t have air going to the blue glad hand when the trailer isn’t hooked up.


    Can someone help explain how it should be plumbed?

    Is there some sort of valve I need?
     
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  3. JamesMc84

    JamesMc84 Bobtail Member

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    Mar 20, 2017
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    From the diagrams I’m looking at it looks like I should t off from the foot valve which goes to a double check valve behind the tractor protection
    Hand valve has air supplied from the supply circuit which T’s into the double check valve
     
  4. JamesMc84

    JamesMc84 Bobtail Member

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    Mar 20, 2017
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    I’m thinking there is a relay I could use, that is T’d into the supply side? Anyone ideas?
     
  5. BoxCarKidd

    BoxCarKidd Road Train Member

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    KIMG0347.JPG You do not have to have a hand valve for the trailer.
    Have to have a tractor protection valve. This is a picture of one on a late 80's KW. It is easy to see. All combination vehicles have one. Many are hid up in the sleeper or cab.
     
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  6. BoxCarKidd

    BoxCarKidd Road Train Member

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    What are wir brakes any ways?
     
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