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Air leak in tractor protection valve

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Ozdriver, Dec 19, 2015.

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  1. Dec 19, 2015 #1
    Ozdriver

    Ozdriver Heavy Load Member

    767
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    Oct 16, 2015
    Australia
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    Here's a question I saw on Reddit/trucking, which seems to be 90% newbies. Anyway, anyone got any ideas? I wouldn't mind knowing the answer myself.

    "For the past few days, I've been hearing a constant hiss coming from my tractor valve. It doesn't happen all the time but if it does, it will go on for the entire day.

    I just brought it into a shop and we could not recreate it no matter what. The guy obviously is writing me off because I don't know much about trucks (only been in one for 11 months), but I know it's there as when it happens, it will happen for ####### hours.

    If I'm driving and it happens, I'll watch the psi drop to 100 then the compressor kicks in and this will happen repeatedly.

    In the shop today, nothing, no leaks whatsoever.

    Am I going crazy or has this happened to someone else? Any tips on how to get it to happen?"

    Someone help the poor guy out lol
     
    Ozdriver, Dec 19, 2015
    Ozdriver, Dec 19, 2015
    #1
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  3. Dec 19, 2015 #2
    mountaingote

    mountaingote Road Train Member

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    If it's hissing through the red valve it's either a bad valve or the trailer has a big leak. That's all that valve does- supply air to trailer
     
    mountaingote, Dec 19, 2015
    mountaingote, Dec 19, 2015
    #2
    Ozdriver Thanks this.
  4. Dec 19, 2015 #3
    Pool6710

    Pool6710 Medium Load Member

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    If you twist them does it go away? Does the trailer have a tire inflation system? Matter if it's warm or cold?
     
    Pool6710, Dec 19, 2015
    Pool6710, Dec 19, 2015
    #3
  5. Dec 19, 2015 #4
    pattyj

    pattyj Road Train Member

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    The shop guy is writing you off?it's not your job to do his job.he's telling you he doesn't know.try tightening the red knob.they do come loose sometimes.
     
    pattyj, Dec 19, 2015
    pattyj, Dec 19, 2015
    #4
  7. Dec 19, 2015 #5
    swaan

    swaan Road Train Member

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    When you say tractor valve , are you talking the yellow parking brake valve .

    If so you have a leak in one of your parking brake maxi pots.
    It will only leak when button is pushed in.
    As soon as you park and pull your button out it will stop.
    To help diagnose it , block your wheels from rolling then release all your brakes then shut your truck off and listen

    It won't leak if you park your truck with your brakes applied
     
    swaan, Dec 19, 2015
    swaan, Dec 19, 2015
    #5
  8. Dec 19, 2015 #6
    ShooterK2

    ShooterK2 Road Train Member

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    He said some days it doesn't do it at all, but some days it does it all day. My guess is that it's the valve itself, and if he will try twisting the knob a little, I'll bet he can get it to stop. If it was a brake biscuit, it would do it all the time, and the shop would have no problem recreating the problem.
     
    ShooterK2, Dec 19, 2015
    ShooterK2, Dec 19, 2015
    #6
  9. Dec 19, 2015 #7
    AModelCat

    AModelCat Road Train Member

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    When I hear tractor protection valve, I think of a valve like the Bendix TP-3, which is the valve that prevents air from leaking out of the trailer service line when bobtailing. Could you clarify that @Ozdriver?
     
    AModelCat, Dec 19, 2015
    AModelCat, Dec 19, 2015
    #7
    ShooterK2 Thanks this.
  10. Dec 19, 2015 #8
    Ozdriver

    Ozdriver Heavy Load Member

    767
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    Oct 16, 2015
    Australia
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    I've got no idea, I was only looking at the guy's post on Reddit. I did come across this YouTube video which explains it pretty good though
    Edit : I imagine the guy on Reddit is talking about the park brake on the dash
     
    Last edited: Dec 19, 2015
    Ozdriver, Dec 19, 2015
    Ozdriver, Dec 19, 2015
    #8
  11. Dec 19, 2015 #9
    AModelCat

    AModelCat Road Train Member

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    Everything he said there was spot on. Is your air leak from the push/pull valves in the dash or from the service line to the trailer?
     
    AModelCat, Dec 19, 2015
    AModelCat, Dec 19, 2015
    #9
  12. Dec 19, 2015 #10
    BoxCarKidd

    BoxCarKidd Road Train Member

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    I used to agree with Shooter 100% but had one trip me up. The driver had been complaining about a similar situation for about two weeks. That truck only traveled 15 miles back and forth as hard as it could go. Numerous people looked at it multiple times, no problem. When I drove it one afternoon it had a sudden air pressure drop and the maxi's were coming on in the road. Found a park brake chamber leaking. After the air was lost it corrected itself and I drove it to the shop. At the shop it worked perfect.
     
    BoxCarKidd, Dec 19, 2015
    BoxCarKidd, Dec 19, 2015
    #10
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