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Mack Engine Brake issue

Discussion in 'Trucks' started by nedly05, Jul 14, 2009.

  1. nedly05

    nedly05 Senior Member

    Joined:
    Jan 28, 2006
    Messages:
    1,791
    Location:
    Adk. Mtns, NY
    My granite has the AMI-370 mack motor, intermittently the high stage goes out, and then the low stage only works with the switch in the high position, and low does nothing. It usually works fine for the first 25 miles or so then it starts to act up, always as I start over a big hill here in town. I will down shift on high, without trouble and as I start down the hill, the high stage quits and only low functions normally, but with the switch in the high position, almost as though a loose wire wiggles with the grade of the hill or something. Hopefully this isnt too confusing!!! Thanks!
     
  2. Muffler Bearing

    Muffler Bearing Senior Member

    Joined:
    Mar 26, 2009
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    274
    Occupation:
    Truck Mechanic
    Location:
    Colorful Colorado
    The best thing you can do is a complete visual inspect, start on the outside and work your way under the covers, check in the dash behind the switches too, you are right it, definately sounds electrical.
     
  3. nedly05

    nedly05 Senior Member

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    Location:
    Adk. Mtns, NY
    Thanks for the input, I was considering looking into it but I'm a little reluctant with all of the electronics. It would be great if it was just in the switch or something simple.
     
  4. nedly05

    nedly05 Senior Member

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    Location:
    Adk. Mtns, NY
    I was talking to another driver today who drives a granite, he says there is an oil pressure line that controls the engine brake, and there is a small valve in that line that gets gummed up. The reason for high cutting out and only low working is that the engine brake is not getting the required oil pressure to function properly. It seems plausible to me.
     
  5. Stevol

    Stevol New Member

    Joined:
    Aug 13, 2009
    Messages:
    3
    Location:
    Pittsburgh
    I have installed an update kit from mack on a couple 350 macks, it was an external oil pressure line from the oil filter housing to the jake stands, seems some of the engines dont get enough pressure and volume to the engine brakes after they are good and hot.
    Not sure if this update kit pertains to your engine model, a call to your mack dealer would tell you that.
     
  6. nedly05

    nedly05 Senior Member

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    Location:
    Adk. Mtns, NY
    Thanks! I still havent had time to get it looked at!
     
  7. nedly05

    nedly05 Senior Member

    Joined:
    Jan 28, 2006
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    1,791
    Location:
    Adk. Mtns, NY
    Took it in the other day, the problem was a bad solenoid on the front head, works like a dream now!!