Trailer protection valve leaking with one of the trailers only

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by montrose818, Jan 20, 2020.

  1. montrose818

    montrose818 Light Load Member

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    31
    Apr 9, 2018
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    My tractor is leaking out the exhaust port when one of the trailers is hooked up during when performing an applied leakage test (truck in gear engine off, valves in, service brake applied).

    I hear absolutely no air loss anywhere but the exhaust port on the Bendix TP5, and it leaks a good amount.

    However, with my other trailer, the tractor performs the test perfect with no leaks.

    What would cause this? I am confused since I found no leaks on the trailer..

    Thank you
     
  2. Swine hauler

    Swine hauler Light Load Member

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    1,025
    Jun 21, 2019
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    It's probably a bad air can on the trailer back feeding through the TP Valve. Try crawling under the trailer with a pair of vice grips and pinch off one service line at a time on each of the cans until you find it.
     
    stillwurkin Thanks this.
  3. montrose818

    montrose818 Light Load Member

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    Apr 9, 2018
    0
    Changed both cans, nada. I should have tested first but the cans looked old and were cheap enough to replace as preventive maintenance.

    It ended up being the relay valve.

    Thank you!
     
    Swine hauler and jsnell Thank this.
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