Losing air while bobtail and detached from trailer.

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by rjustin140, Nov 28, 2020.

  1. rjustin140

    rjustin140 Bobtail Member

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    2015 international prostar Cummins isx15

    like the title says. Trying to chase a new leak. Takes half a day to completely leak out. When I’m attached to a trailer it doesn’t leak. Any suggestions?
     
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  3. daf105paccar

    daf105paccar Road Train Member

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    Trailer air supply line
     
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  4. Rideandrepair

    Rideandrepair Road Train Member

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  5. truckdriver31

    truckdriver31 Road Train Member

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    you got a leaking dry rotted air bag. the weight of the trailer pushes down air bag. look and spray where the folded part is. top and bottom. when your bobtailing around. the bag is taller. exposing small cracks
     
  6. magoo68

    magoo68 Road Train Member

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    Levelling valve on suspension ..
     
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  7. Hammer166

    Hammer166 Crusty Information Officer

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    Ummmmm, air bags run the same height all the time, that's why there's a leveling valve?

    I second the tractor protection valve as the culprit. Anything air suspension related will be worse hooked up due to higher weight / pressure.
     
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  8. Roberts450

    Roberts450 Road Train Member

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    They do ride at slightly different heights depending on weight. Its not a big difference maybe a half inch or so, leveling valves aren't that precise.
     
  9. truckdriver31

    truckdriver31 Road Train Member

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    so i guess you never had a dry rotted cab or rear axle bag lose air.
     
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  10. Hammer166

    Hammer166 Crusty Information Officer

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    Plenty. And always worse with higher pressures.
     
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  11. Hammer166

    Hammer166 Crusty Information Officer

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    It's not the weight, it depends more on where the suspension happens to be within the very small dead zone in the center of the leveling valve and/or slop in the linkage. They are a lot more precise than you think, it's much more common to see a loose arm causing varying ride height than the valve itself. I run a carhauler, changes in ride height are quite obvious as low to the ground as I am, and it's remarkably consistent.
     
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