Air leak

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by FREDthaCEO, Mar 6, 2021.

  1. FREDthaCEO

    FREDthaCEO Bobtail Member

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    Mar 6, 2021
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    I have a 07 Freightliner Columbia , my truck builds air pressure VERY slow and slowly leaks out, I can hear the leak behind the dash but a mechanic is telling me he thinks it the air compressor but I don’t hear any funny noises coming from my air compressor. Any thoughts ? And what are other signs that my air compressor could be bad
     
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  3. pavrom

    pavrom Road Train Member

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    Pull the dash and start there!
     
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  4. GYPSY65

    GYPSY65 Medium Load Member

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    The sound you hear behind the dash does not mean that’s where the leak is
    That’s an indicator that you have a leak somewhere

    When do you hear the leak? When trailer or truck brakes released or all the time?
     
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  5. FREDthaCEO

    FREDthaCEO Bobtail Member

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    When I first crank the truck up and build the air I hear it and also when I push the parking and trailer brakes in. So all the time I guess
     
  6. A5¢

    A5¢ Medium Load Member

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    Charge up your trucks air system with a shop air compressor and do not start the truck. Block the tires, push in the parking brakes and start listening for leaks.
     
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  7. loudtom

    loudtom Road Train Member

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    I'd start by cutting off the air to the trailer. Then get a bottle of soapy water and start spraying every air connection on the truck, as well as the rubber on the air bags. If you see bubbles, you want to fix that leak. If you still hear air under the dash after fixing the leaks, you'll have to get under the dash and check the connections. You should be able to use your hand around the fittings if you don't want to spray soapy water under there, and it will change the sound when your fingers run over the leak. If it sounds like it's near the foot pedals, check the pressure sensors in the firewall and pass through area. If it sounds like it's up high, check the dash valve, as well as any elbows or tees on the air lines. If your seats are air operated, don't forget to check the lines to them.

    Do the same procedure for the trailer after supplying air to it. You'll also want to spray the gladhand seals and lines, and the protection valve on the tractor side of the lines. When the trailer leaks have been fixed, you'll want to go inside and listen for leaks under the dash again.

    Then I would look at the parking brakes. Make sure the wheels are chocked and the truck cannot move. Release the tractor brakes (yellow knob in), cut supply to the trailer (red knob out). Now go under the truck and spray the brake chambers and the lines coming off of them. Fix or replace any parts that are leaking. You can do the same for the trailer if you didn't check them earlier(yellow knob out, red knob in).

    Finally, I would check the service brakes. Make sure the wheels are chocked, and press both knobs in. Let the air build up to full, then hold down the brake pedal. Watch the gauge for your air tanks and make sure it's not losing air while you keep the brakes held down for a minute or so. If it is, you'll want to grab a helper, so that one of you can listen and spray the area while the other person keeps the brakes held down. You could probably do it yourself with the right tools and/or creativity, just make sure the wheels are chocked.
     
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  8. uncleal13

    uncleal13 Road Train Member

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    Every trucker should get an Ultrasonic Leak Detector. They work great and save hours of time.
    I used mine on a friends truck recently, couldn’t find anything. Then while circling the truck a third time he had the drivers door open and I homed right in onto his parking brake valve. You still couldn’t hear it once I knew where it was, but the detector found it in a flash.
    TruTrack™ Ultrasonic Leak Detector | Robinair
     
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  9. FREDthaCEO

    FREDthaCEO Bobtail Member

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    Thanks everyone comeTo find out it was a leak in my governor
     
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