How to tell when airbags need to be replaced?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Thetrashnoob, May 5, 2021.

  1. Thetrashnoob

    Thetrashnoob Light Load Member

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    I recently purchased a tri axle dump truck, currently still waiting to get it on the road just doing little things here and there. I’m having an issue where if the lift axle is up and the truck is aired up (120 or so) within 2-3 hours the axle is lowered and the primary air is usually between 90 and 60 or less psi. I’ve been trying to track down the leak but haven’t had much luck, if it’s losing that much pressure I feel as if it would be a fairly noticeable leak, and you’d be able to hear it. I’m starting to think possibly the bags? See attached photo. I know it could be 1,000 different things but if it’s losing that much pressure that quickly surly it should be noticeable?
     

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  3. God prefers Diesels

    God prefers Diesels Road Train Member

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    Temporarily adjust your leveling valve so they jack up higher, and spray the new rubber that gets revealed.

    My truck leaks faster than yours, and I only have one barely audible leak on my air tank. Good possibility you won't hear yours.
     
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  4. Happily Retired

    Happily Retired Road Train Member

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    Soap bubbles will tell you in short order,,,
     
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  5. Mattflat362

    Mattflat362 Road Train Member

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    I found mine driving in the rain with no load on them. When loaded, the bottom of the bag sealed against the base and stopped the leak.
     
  6. God prefers Diesels

    God prefers Diesels Road Train Member

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    Also spray the top metal part of the bag. I guess they corrode and leak there as a rule, before the rubber leaks. That was also the case on my trailer.
     
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  7. Thetrashnoob

    Thetrashnoob Light Load Member

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    When the axle is up I can’t hear anything from the bags, although I do have a leak in the cab for the pressure regulator and the switch for the lift axle, but again only when the axle is down I can hear it. but lower the axle and I can hear this, I can’t tell if it’s coming from the bags, or something else. It’s hard to tell without lifting the box, and my box prop is very janky and I do not want to be under there! Not sure if this link will work but here’s the leak with the axle down.
    https://photos.app.goo.gl/tfojhvghDywQrtdu7
     
  8. jason6541

    jason6541 Road Train Member

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    Willing to bet from years of dirt rocks and such. The base of air bags have been rubbed thru outer layer. Inflate bags to maximum height and spray with soapy water. Base crimp around bag seat is leaking or the rubber is compromised and
    Leaking thru.
     
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  9. Don379

    Don379 Medium Load Member

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    Those bags are pretty new on your lift axle. I have same setup. When they get really old, you will see dry rot around the edges that curve. Even so, those aren’t the bags that keep raise and keep axle lifted. Those are pancake style bags located in lift axle frame just forward of the tires. That leak sounds like it’s coming from the box with electric solenoid that distributes air to your axle It’s located on frame in middle of lift axle. Put your bed in the air. If you don’t feel comfortable with your prop, then put blocks of wood further down on rail under the box. Your gonna have to work under the bed from time to time. So yeah, your gonna have to trust your safety mechanisms. Don’t fiddle with hydraulic lines when have the bed in air and not sure about the prop.That’s when people die.
     
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  10. Thetrashnoob

    Thetrashnoob Light Load Member

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    This is going to sound like a dumb question, but what exactly do you mean inflate them to max height? I’m not sure how you do that with a lift axle?
     
  11. Thetrashnoob

    Thetrashnoob Light Load Member

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    FC616847-B78D-4206-8783-B1D4B38EFA8C.jpeg
    Yeah the bags do look fairly new, and I know those aren’t the bags that raise the axle. But the bags look squished when the axle is down, and they don’t really look right to me, but maybe that’s how they are supposed to be. I’ll have to try using the prop, it just looks very flimsy and not sure how trustworthy it is. I may have to get some blocks and do that in the future. Why would the air leak only be noticeable when the axle is down but not up? I will have to check and look for that solenoid.
     
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