1985 Big Cam Cummins

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Notiller12, Jun 6, 2026.

  1. Jun 6, 2026 #1
    Notiller12

    Notiller12 Bobtail Member

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    I have a 1985 Freightliner Flc120 and it has a 340 big cam with Jacob’s engine brake. Once in a while the Jake brake will start sputtering and going on and off. Other times it don’t bother. I’m looking for a diagram of what to trace. Thanks
     
    Notiller12, Jun 6, 2026
    Notiller12, Jun 6, 2026
    #1
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  3. Jun 6, 2026 #2
    062

    062 Road Train Member

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    062, Jun 6, 2026
    062, Jun 6, 2026
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    OLDSKOOLERnWV Thanks this.
  4. Jun 6, 2026 #3
    OLDSKOOLERnWV

    OLDSKOOLERnWV Captain Redbeard

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    Does this happen while you’re driving?
     
    OLDSKOOLERnWV, Jun 6, 2026
    OLDSKOOLERnWV, Jun 6, 2026
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    062 Thanks this.
  5. Jun 6, 2026 #4
    Notiller12

    Notiller12 Bobtail Member

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    Yes when I’m using the engine brake to slow down with a loaded trailer.
     
    Notiller12, Jun 6, 2026
    Notiller12, Jun 6, 2026
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    OLDSKOOLERnWV Thanks this.
  7. Jun 6, 2026 #5
    OLDSKOOLERnWV

    OLDSKOOLERnWV Captain Redbeard

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    Oh ok. Look at the little things first.

    You should have 2 micro switches, 1 on the pump operated by the throttle, and 1 on the clutch pedal.

    Check to make sure they are adjusted properly, and insuring the clutch pedal return spring is has not broke or gotten weak.

    Had a similar issue some years ago and had to add spring to the clutch pedal….
     
    OLDSKOOLERnWV, Jun 6, 2026
    OLDSKOOLERnWV, Jun 6, 2026
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    Big Road Skateboard and 062 Thank this.
  8. Jun 6, 2026 #6
    OLDSKOOLERnWV

    OLDSKOOLERnWV Captain Redbeard

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    Also look at your wire connections out on the Jake’s, be on right / passenger side…..
     
    OLDSKOOLERnWV, Jun 6, 2026
    OLDSKOOLERnWV, Jun 6, 2026
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    062 Thanks this.
  9. Jun 7, 2026 #7
    Notiller12

    Notiller12 Bobtail Member

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    Ok thanks I will look into it. I already checked the head connections and they were good, but now I’ll be looking at the clutch and fuel pump. Thanks
     
    Notiller12, Jun 7, 2026
    Notiller12, Jun 7, 2026
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    Bean Jr. Thanks this.
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