Strange air leak

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Freightlinerbob, Dec 9, 2015.

  1. Freightlinerbob

    Freightlinerbob Road Train Member

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    The leak is on the "B" reservoir. Here are the symptoms:
    -Driving down the road the compressor cycles every few minutes.
    - When parked with parking brakes applied, it leaks just as fast.
    - When parked with parking brakes released, the leak seems to stop, more or less. (30 minutes to leak from 120 to 100 psi. )

    I've sprayed down everything I can think of with soapy water and can't find anything.

    Any ideas?
     
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  3. mountaingote

    mountaingote Road Train Member

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    Sounds like a valve problem
     
  4. Freightlinerbob

    Freightlinerbob Road Train Member

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  5. AModelCat

    AModelCat Road Train Member

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    Is B the primary or secondary reservoir?

    Have you checked the exhaust ports for leakage at every valve you can find? I would guess that maybe you have a valve that's leaking. Possibly a check valve in the air system sticking, which would cause you to only draw air from the B tank rather than blended air from both for the trailer supply or air accessories such as suspension.
     
  6. baha

    baha Road Train Member

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    CK. your firewall for air leaks from dash valve ex. line plastic line that is ending outside firewall so you will not hear air release from air brake valve inside dash so any leaks can be heard at eng. side of firewall, also ck. foot valve ex. port for leak?
     
    Last edited: Dec 9, 2015
  7. Freightlinerbob

    Freightlinerbob Road Train Member

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    Yea the B tank is the secondary tank.

    I should mention that when parked with parking brakes released and the suspension relaxed the air is not leaking. It doesn't matter if the engine is running or off, it does not leak. This is just as if the truck was driving except that it isn't moving. Yet when it is moving, it leaks.
    Now I just parked it without applying parking brakes and let it settle for 10 minutes, then applied the parking brakes. The air leak is significantly reduced. Although it still leaks somewhat.
    I'm thinking its in the air suspension.
     
  8. Ozdriver

    Ozdriver Heavy Load Member

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    It can be hard finding an air leak in an airbag especially when there's no weight on it. I've had to isolate each airbag in turn before I found a leak. I would first be isolating the whole suspension system from it's air supply as a first off. You'll need some 1/4" or 3/8" blanking plugs for this.
     
    AModelCat Thanks this.
  9. swaan

    swaan Road Train Member

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    Could be bad leveling valve .
    Park it and dump the air in suspention.
    Air ride cab??
    Could be leveling valve on there too.
     
  10. Freightlinerbob

    Freightlinerbob Road Train Member

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    Cab air bags and valve are new. I've double checked them as well. Parked with air suspension dumped. This made no difference, so I'm back to thinking its not the suspension.
     
  11. Ozdriver

    Ozdriver Heavy Load Member

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    It isn't unheard of for the air from the primary tank to bleed back into the compressor. You could disconnect the line from the compressor port and see.
     
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