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air compressor problem

Discussion in 'Truck Talk' started by LCharles, Jun 29, 2004.

  1. LCharles

    LCharles New Recruit

    Last month I was driving a class 8 Freightliner expediter straight truck with a 96" condo. I noticed that about once a minute an air release valve would open with a hiss and the top air gauge indicator would move downward.

    After about a minute, the air gauge would build up and show about 140 pounds and what I assume is a pressure safety valve would release again.

    This cycle continued every minute when driving the truck for the month I was on the road with the owner/operator.

    He said it was supposed to be that way.

    I'm not so sure.

    Another problem was that when slowing down quickly to avoid a vehicle dead stopped in front of me, a loud banging noise came from the rear underside of the truck.

    We were carrying about 12k lbs. The o/o set the air pressure in the tag axle bags at 40 psi.

    If I applied the brakes harder in that case, on the very rough road, the banging got louder. And so did the yelling from my boss.

    I tried to brake more lightly, that seemed to help, but there was still the problem with traffic so I had to slow down.

    The noice from my owner/operator continued.

    What could I do to prevent that?

  2. RichM

    RichM Expert Expediter Charter Member

    I am pretty sure you have a leak.When the truck sits all night without the engine running do you still have air pressure in the AM?
    The purge valve in the Air Dryer is notorious for giving problems,I have gone through about 3 of them and carry a spare with me. Does it leak air with no load on and while you are idleing? If the owner is satisfied with strange noises and problems ,let it go.You did your job reporting the problems.
  3. davekc

    davekc Senior Moderator Staff Member Fleet Owner

    sounds like a bad air regulator or bad brake chamber. That would explain the bang. I would have it checked out if you don't know what you are looking for on the brake chamber. They are not expensive and can be repaired quickly. With the bang, it doesn't sound like the hoses. You can always check by spraying some water and soap on the lines and see if they leak.
  4. LCharles

    LCharles New Recruit

    I'm not on the truck anymore. The boss blew a fuse when he heard the banging, which continued bang bang bang when I was applying the brakes. He said I didn't know how to drive and was hurting his truck. The rest was a string of obscenities.

    Very rough road. Only happened that one time, down a slight grade, car stopped quickly dead in front of me. Vehicles on both sides, no place to go.
  5. LCharles

    LCharles New Recruit

    I did hear a hissing noise from the air bag area when we were loading. Don't remember about the overnight air gauge levels.

    The lower gauge stayed about 120 psi all the time.
  6. RichM

    RichM Expert Expediter Charter Member

    As the truck is loading you may hear air hissing into the bags.This is normal as the weight increases they require more pressure to maintain the ride. They generally fill from one of the holding tanks which in turn gets resupplied from the compressor.\But since you quit this guy, which sounds like a good decision,don't loose any sleep over it.
  7. davekc

    davekc Senior Moderator Staff Member Fleet Owner

    How does driving the truck effect brake noise? Sounds like a interesting owner?
  8. RichM

    RichM Expert Expediter Charter Member

    Another problem that could be, is if your air bags are not holding pressure ,on a panic stop the rear axle could lock up and if you hit a bump the box would go up and slam back down on the springs etc.
  9. ClassicOne

    ClassicOne New Recruit

    the hissing sounds like the compressor "kicking in" to build pressure. The popping sounds like the governor doing its thing with the following pressure "blowoff" from the dryer. My concern would be the number of cycles and pressure limits. With rough roads and heavy weight my truck's air compressor will cycle often, but not on smooth roads. The increased need for makeup air pressure to the bags on both the drives and tag can cause greater air usage.
    My experience with rough roads is the tag air pressure needs to be higher as the tag will jump during hard braking and pound like the dickens!!! scares the hell out of you if you don't know what is happening. should have been more like 60-65psi to help stop the tag axle bounce.

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