Trailer air supply problem

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by RGVTrucker956, Oct 23, 2021.

  1. RGVTrucker956

    RGVTrucker956 Bobtail Member

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    Sep 17, 2016
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    Have an 03 Peterbilt 379 & it’s not supplying enough air to trailer in order to release brakes.
    Air does build with no noticeable air leaks to the ear, but when I supply air to red line it quickly drops too much, not giving enough air to trailer. Hooked up another truck to same trailer & all works as it should. Anyone know where the problem might be? Thanks in advance.
     
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  3. Goodysnap

    Goodysnap Road Train Member

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    Block the red gladhand off on the truck side and charge the trailer brakes and inspect for leaks. You can do the same on the service side but it sounds like your issue is with the emergency.
     
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  4. AModelCat

    AModelCat Road Train Member

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    If the trailer has no air pressure in its tanks it can take a minute or 2 to charge the trailer before the brakes release. An empty trailer system can easily drop a fully charged tractor down 30-40 PSI until they equalize, then the compressor builds the rest.

    When was the last time you drained your truck's air tanks? I've seen them fill up with condensation, which reduces capacity and causes a huge pressure drop in the truck when charging the trailer air system.
     
  5. MRMTRANS

    MRMTRANS Light Load Member

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    Apr 28, 2015
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    I've had the supply valve on my trailer go bad once.
     
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