ABS valve leaking air

Discussion in 'Peterbilt Forum' started by Loaderlou, Feb 22, 2019.

  1. Loaderlou

    Loaderlou Medium Load Member

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    Feb 24, 2014
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    Hi everyone. My ABS valve is leaking air to the point when I turn the truck off with the air brake button in the release mode, the pressure drops from say 100 #’s (not hashtag, pounds) to 30 in a matter of 10 to 15 seconds. It’s not the modulator valves it’s the ABS valve itself. I just changed the whole group out 7 months ago and I also changed out the quick release valve. I’ve been told if one leaks change the other and visa versa. How about a bad air can? All opinions appreciated, thanks
     
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  3. swaan

    swaan Road Train Member

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    BC canada
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    Yes it's a maxi pot with a bad diaphragm. Its bleeding back into the service side and going out your abs valve. This is why it only leaks with yellow dash button pushed in. It's rare but does happen. I just changed one 2 weeks ago.
    If you want to make sure just put a vise grip on the line going to your maxi pot and see if it stops
     
  4. QUALITYTRUCK

    QUALITYTRUCK Road Train Member

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    romulus,mi
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    Exactly what Swaan said. Follow that procedure and you will find your problem. You might be lucky and only have 2 30/30 chambers in back instead of 4. Cut down on diagnostic time.
     
  5. Loaderlou

    Loaderlou Medium Load Member

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    Feb 24, 2014
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    Thank you guys for the comeback. I will try that today. I also need to change my compressor as it is starting to bleed oil. Full day of work ahead of me. Thanks again I’ll let you know how I make out
     
  6. Loaderlou

    Loaderlou Medium Load Member

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    Feb 24, 2014
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    Just pinched off the service lines one by one and when I pinched off the front driver side the leak stopped. When I released the visegrip it sounded as if I took my foot off the brakes and no more leak.
     
  7. swaan

    swaan Road Train Member

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    Your yellow button probably popped at same time. Sounds like you found it.

    What I usually do is if all 4 your pots are same age , replace them all. I cant seem to get more 4-5 years out them.
     
  8. Loaderlou

    Loaderlou Medium Load Member

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    Feb 24, 2014
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    I think you’re right. And yes I agree about the longevity of the chambers. On my list as well as maybe having to change some or all of the air valves due to the oil from my compressor. It never ends. Thanks for the help
     
    Another Canadian driver and swaan Thank this.
  9. LostSouls001

    LostSouls001 Bobtail Member

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    Jun 3, 2019
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    Having this problem now on my Y2K W9, just read all your comments going to pinch some air lines now. Be right back..
     
  10. LostSouls001

    LostSouls001 Bobtail Member

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    Jun 3, 2019
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    OK, when I pinched off the right parking brake on rear drive it stopped leaking from ABS valve, so I will change out the chamber tomorrow. Will report results..
    Thank you..
     
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