waste of brake shoes

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by opertom, Dec 13, 2019.

  1. opertom

    opertom Bobtail Member

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    ...business advice, that's it. I'm also in the business of keeping small problems from becoming big ones, and right now the trailer brakes won't fully release until the red air button is pulled and re-pushed with a full tank of tractor air.

    Obviously this can't be done in transit.

    The drag is very slight. It's only one tractor in the overworked fleet manager's inventory. The distance is only about a mile per trailer and many trailers are brought in by drivers who ride the trailer brake anyway so obviously this can't be a high-priority issue.

    Nevertheless waste is occurring with every unnecessary brake shoe replacement and unnecessary release of stink into the atmosphere. Can anyone explain this?
     
  2. BoxCarKidd

    BoxCarKidd Road Train Member

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    So multiple trailers have this problem?
     
  3. GypsyWanderlust

    GypsyWanderlust Medium Load Member

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    If I understand correctly and this is an issue with a specific tractor then check the emergency air pressure at the glad hand and make sure it is getting the correct pressure. If I remember correctly, anything less than 60 psi will let the spring bakes start to drag. You can probably spin off the glad hand and put a gauge right on the line.

    If the pressure is low, check for leaks. If there is a pressure regulator check that as well.
     
    Last edited: Dec 13, 2019
  4. opertom

    opertom Bobtail Member

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    Apr 26, 2013
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    Yes, one tractor in question. The issue's has come up from time to time but it's been at least a year since I've dealt with it.

    Might scout around for a screw-on gauge, good. The idea being to check pressure and recovery time before and after stepping on brake? The issue isn't really an issue when the trailer is initially charged.
     
  5. xsetra

    xsetra Road Train Member

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    My truck was causing the trailer to drag the brakes.
    I replaced the air valve the brake pedal is attached to.(treadle valve)
    I also cleaned the Piston/rod that the pedal pushes in to that valve.

    It didn't always stick. Sometimes just enough for the brake lights to stay on. Sometimes I could feel the drag from the brakes applied.

    Most of the time normal operation.

    Good luck
     
    baha Thanks this.
  6. Working2party

    Working2party Medium Load Member

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    I’m guessing it’s one of the little valves in the back of the park brake control button assembly. They do a few jobs, but one of them is to pop out the button in the event of a massive air leak on the tractor (to save the air in the tractor) This assists the tractor protection valve on the back of the cab. There’s a chance, if your on a paper thin parts budget, you could take the park brake valve assembly completely apart, clean it and re-grease the O-rings and fix it. Probably wouldn’t hurt to do tractor protection valve also. But those should be the only valves that could cause this issue.
     
  7. spsauerland

    spsauerland Road Train Member

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    Is the trailer valved with spring brake priority or service brake priority?
     
    pushbroom Thanks this.
  8. SmallPackage

    SmallPackage Light Load Member

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    Could be a dirt dauber plugged or partially plugged the end of the exhaust hose for the trailer hand brake valve just enough to hold pressure to trailer brakes only. If the tractor has an application gauge on dash it may show a slight constant psi when park brakes are not set and you are not pressing the foot valve or pulling on the hand valve.
     
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