Mack will only build air when pumped down to nearly 5psi

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by bust7015, Sep 16, 2021.

  1. bust7015

    bust7015 Bobtail Member

    2
    0
    Sep 16, 2021
    0
    :dontknow: Hello all. Scratching my head on this one. I have a 1986 Mack Superliner triaxle that will not build air unless the system is pumped down to nearly empty. It builds to 125psi as it should. The compressor has less than 30k. The unloader valve is clean and I have replaced the governor twice. It also has a brand new air dryer. The lines appear to be clear and yet this keeps happening. Any thoughts are appreciated.
     
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. Magoo1968

    Magoo1968 Medium Load Member

    391
    924
    Mar 18, 2021
    St Malo mb
    0
    Faulty governors or plugged signal line to governor seems like the most logical. I’d disconnect the signal line and see if compressor starts pumping. If it doesn’t it must be governor or it’s adjustment.
     
    beastr123 Thanks this.
  4. bust7015

    bust7015 Bobtail Member

    2
    0
    Sep 16, 2021
    0
    I disconnected the signal line. The compressor pumps just fine. I tried a third governor and the same problem occurred. All the lines blow clear.
    I did just find something out… I was away while the truck went out for a new frame. Turns out the builder replaced some airlines between the tanks. Maybe he hooked up some lines incorrectly? Even so, the lines going to the governor are in the correct location.
     
  5. BoxCarKidd

    BoxCarKidd Road Train Member

    3,499
    4,849
    Aug 26, 2014
    0
    I thank the line to the control port should go to the wet tank. That line goes off the center port opposite the vent or exhaust port. Center ports go to the compressor and air dryer to unload.
     
    spsauerland Thanks this.
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  • Draft saved Draft deleted