2018 Freightliner secondary air leak only when moving

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by towtrucker, Mar 18, 2019.

  1. towtrucker

    towtrucker Light Load Member

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    Mar 25, 2012
    boston ma
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    I was hoping for some help on an air leak on a 2018 cascadia. It has the 12 liter engine and automated 12 speed transmission. When driving down the road at the truck will start to loose air in the secondary system only. It is a significant leak.
    The leak does not start right away.
    Once it builds back up it will hold pressure for a minute or so then start to leak again
    When stopped even with parking brake released on the tractor it will not leak any air and will pass a pre trip leak down test.
    I run with multiple trailers and the problem does not change with different trailers.
    Any one have any ideas on what could be leaking or where to start ? Any help would be appreciated.
     
    Eugeniu and uncleal13 Thank this.
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  3. xsetra

    xsetra Road Train Member

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    Search the internet
    ...Bendix air brake system trouble shooting...

    Good luck.
     
  4. uncleal13

    uncleal13 Road Train Member

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    I have a 2016 doing the same thing. But I am suspicious of the ABS valve on my lead trailer. Only leaks when I don't have time to look for it. Doesn't leak when I have the time.
     
  5. Working2party

    Working2party Medium Load Member

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    All your accessories run off the secondary. So I ask, how rough of roads are you traveling? Are your trailers air ride also? The tougher the roads the more air passes through your suspension.

    Your trucks new enough it should not have air operated vents or air assisted DEF injection, so basic factory accessories leaves your with cab, rear, and trailer suspensions as your culprits.

    It could be a brake chamber, but that would leak while stopped (wheels chalked and brakes released).

    So unless I’m forgetting something... (which happens to often) this is normal.
     
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  6. x1Heavy

    x1Heavy Road Train Member

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    A small correction on brake chamber. From the specific experience I had with a leak that originated in the rubber divider between the service chamber and the spring brake chamber. It became a real problem when applying either the trolley or the service braking. It also involved the primary air in a hurry.

    I need to find that Federal Inspector to straighten me out on a couple of burrs in my saddle from that incident. I don't understand why I did not lose all my air all the time after releasing those spring brakes back there.
     
  7. uncleal13

    uncleal13 Road Train Member

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    Figured out today that my secondary leaks down rapidly only when the transmission is in high range. In low range moving around in a yard in doesn’t budge, as soon as I get into high range, then the pressure drops.
    The compressor cycles every four minutes.
    Problem is I have an Eaton UltraShift, so I can’t make it go into high range when stopped to see where the leak is.
     
  8. xsetra

    xsetra Road Train Member

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    Deleted
     
    Last edited: Mar 20, 2019
  9. towtrucker

    towtrucker Light Load Member

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    boston ma
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    Well 2 trips to the dealer and still have the leak. The first time in I was told no problem found. So I took a video of the leak while driving and went back. They told me it was a maxi can . It wasn't the truck has the same transmission as uncleal13. We will try again. SMH
     
  10. PE_T

    PE_T Road Train Member

    Every time you have an air leak or a tire leak, it is recommended that you know where the leak is. If the mechanic can’t find it, there nothing that he can do, but charge you for the 1-2 hrs he spent looking for it. I’ve been through this like 4 times when I was a new driver.

    You can either try to find it yourself, or find a very experienced mechanic. Those guys typically work the day shift. Go to a TA/Petro at 8am (start of day shift), and request for their most experienced mechanic. Now, if you want to find it yourself, I posted a couple comments a few months ago that can help you find the air leak.

    Suspension air bags deflating
     
    Last edited: Mar 28, 2019
    Reason for edit: Typo
  11. uncleal13

    uncleal13 Road Train Member

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    I’m still waiting for the o-ring kit to arrive to see if I can fix mine.
     
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