ABS and Low air problem

Discussion in 'Experienced Truckers' Advice' started by krazman, Apr 23, 2008.

  1. krazman

    krazman Light Load Member

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    Dec 11, 2007
    Wichita,Ks
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    HI;
    Can anyone tell me why I have an ABS light on most of the time ? My brakes do not lock up , they do not stop the truck fast either. Real mushy, like a car with low brake fluid.
    Air pressure stays around 95 to 100 most of the time and occasionally goes up to 125 for a while. Makes it real hard to stop .
    My boss says the brakes are adjusted but I think not. I tried to auto adjust them by backing up fast and stomping on the brakes but it did no good.
     
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  3. Cub

    Cub Bobtail Member

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    Jan 9, 2008
    Central Florida
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    I'm not even a trucker yet, but I have to ask - Isn't that a question the rig mechanics should have the answer for?

    God bless and be safe,
    Cub
     
  4. gearjammer-2000

    gearjammer-2000 <strong>Clutch User</strong>

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    Dec 18, 2007
    columbus Ohio
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    well first off you are the one responsible to make sure the brakes are adjusted properly so I would suggest that you crawl under the truck and measure the throw yourself after all it will be you not your boss paying the fines,
    as to the rest of what you said it sounds like the whole system is a mess could be anything to a bad compressor, bad regulator bad brake chamber blown airline those are some of the possible explanations for the low air pressure,as to the light could beas simple as a bad sending unit to computer problems, the truck sounds unsafe to be on the road and if you happen to kill someone it will be your butt in the slammer for years not your bosses get the thing looked at by a professional
     
  5. GasHauler

    GasHauler Master FMCSA Interpreter

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    Vegas/Jersey
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    The first thing I would do is a leak test. Build your pressure up over a 100psi. Release the brakes, apply the foot brake and shut the engine off. Make a note on where the neddle is exactly. Wait a couple of minutes and see if you have any air loss. If you do you'll have to get it fixed. You can loose 2psi in one minute for a single vehicle or 3psi for combinations anything over needs to be fixed. There are no adjustments you can make to the brakes with automatic slack adjusters. Either they work or they don't. We found an important message sent out about adjusting automatic slack adjusters. If they are adjusted like the old system you will cause them to not stay adjusted and will have to replace it.

    Make sure you do a complete inspection of the truck before you turn it over to the shop. You'll also want to be clear on what you've done so far to make you believe you've got a brake problem.
     
  6. krazman

    krazman Light Load Member

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    Dec 11, 2007
    Wichita,Ks
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    Just a guy with 5 trucks. No mechanics. Just looking for a good place to start checking out. Figure someone would know what the problem is. I had a 2006 freightliner that the ABS light came on all the time. Never figured it out but it did not seem to cause any problems. This KW however is running at 95 to 100 pounds of air for some reason. Loses air fast after turning it off. Must have a leak.
     
  7. witchwaywest

    witchwaywest Medium Load Member

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    Dec 8, 2007
    Monroe New York
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    ABS problems.A bad or dirty wheel speed sensor will cause the dash light to come on.Even if you do have a problem with ABS you will still have your primary and secondary brake systems operating.You can brake in the normal manor but you will not have the benefit of ABS,which controls wheel lockup on each axle.If your brakes are out of adjustment or your brakes components are worn then you may have a hard time during a hard braking application.The tractor may steer in the wrong direction or the trailer may come around.Auto slack adjusters can go bad but it's more likely that the brake components are worn.As far as air pressure,125 psi is a normal range for the compressor to cut out and 95psi to 100psi is when it should kick back in.It does sound like you have an air leak.It could be something as simple as a glad hand washer or worse,a brake cannister diaphram or a bad line.The tractor and or trailer should go to the shop,which I hope you do.Until then try this for the air leak.Park the tractor.Chock the wheels.Release the brakes after the air tanks are fully charged.Take a spray bottle,soap and water,and spray each air line component with this.You will see air bubbles at the site where the leak is.Repeat the process,you might have more than one.Again,the tractor and or trailer need to be put out of service.If the boss says no,pull in to an inspection station,state the problems.They will be more than happy to put you out of service and I am sure your boss will make the needed repairs.If you are the boss and you think the cost is to much,think about the liabilty to your business.
     
  8. Lurchgs

    Lurchgs Road Train Member

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    Feb 13, 2008
    Denver, CO
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    Absolutely what GearJammer and the others have said.

    ABS is something that needs to be fixed - next time it's in the shop.

    Low air pressure and mushy brakes is something that calls for a trip to the shop NOW.

    As for normal cut-in for compressors... I can't say from experience. I know the pre-trip inspection in Colorado requires that you check the fill rate - which must be 85 psi to 100 psi in less than 45 seconds. Cut-in on all the school's trucks was below 80. Cut-out also varied - between 115 and 130.

    Of course, it would help if the dad-blasted gauges had more markings than 0-25-50-75-100-125. A hash every 5 psi would be wonderful. Measuring 3 psi (or 4, if the truck is on but not running) change is a matter of pure guesswork, no matter your experience, when the hashes are 25 or 50 PSI apart.
     
  9. broncrider

    broncrider Road Train Member

    i would start the low air pressure search by throwing a $20 part at it....get an air governor from your local napa, a few air lines and two bolts are all that need to be removed and replaced....that should at least fix the cut out back to 120-125 psi...if you can read/follow printed instructions...you CAN do it

    i would then manually adjust all brakes...this is not something to do every week with auto's as it will destroy them..re check after some miles...if back out, replace the slack

    as far as the ABS...take it to a shop and have them do it, but i'll bet its just a case of bad input (i.e. dirty ring or sencor, ground fualt or something else you wont know unless yer plugged in)
     
  10. D16

    D16 Light Load Member

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    Jul 11, 2007
    Vancouver
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    In my Volvo ABS light appears only when I hook trailer with failed ABS.:yes2557:
     
  11. GasHauler

    GasHauler Master FMCSA Interpreter

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    Vegas/Jersey
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    Better get it fixed since the air loss is an out of service item. You could charge the trailer brakes set the tractor brakes then pull down on the trolly bar or brake hand valve get out and try to hear where the leak is. Then if you don't hear anything I'd set the trailer brakes, charge the tractor brakes then shut it off apply some brakes then listen. If you haven't found a simple fix then time for the shop.
     
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