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85 K20 Suburban with AC

Discussion in 'Tech Discussion' started by Brother Bill, Jan 15, 2021.

  1. Brother Bill

    Brother Bill Junior Member

    Posts:
    3
    Likes Received:
    0
    Joined:
    Jan 9, 2021
    Location:
    NM
    First Name:
    Bill
    Truck Year:
    85
    Truck Model:
    K20 Suburban
    Engine Size:
    350
    I'm struggling. I just bought the above suburban and I'm sorting through issues one at a time.

    There is a wiring harness (with a vacuum hose) that passes through the firewall below the fuse box. It routes up into the dash and disappears.

    In the engine bay the hose is not connected. It is bent like it was originally tied to the vacuum port on the manifold, so I thought I'd reconnect.

    Afterword when i pressed the brake it sounded like a vacuum or air leak someplace down by the brake pedal. So I disconnected again. I can't trace it down under the dash without really tearing the dash apart.

    Anyone help me?

    tks
     
  2. Slow build jim

    Slow build jim Member

    Posts:
    45
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    34
    Joined:
    Jun 22, 2017
    Location:
    Doylestown ohio
    First Name:
    Jimmy
    Truck Year:
    85
    Truck Model:
    K10 Silverado
    Engine Size:
    454
    Sounds like your cruise control.
     
    bucket likes this.
  3. PrairieDrifter

    PrairieDrifter Full Access Member

    Posts:
    1,806
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    1,016
    Joined:
    Dec 28, 2014
    Location:
    North Dakota
    First Name:
    Mason
    Truck Year:
    84,79,77,70,48
    Truck Model:
    Suburban k10, bonanza k10, c30 C&C, c10, gmc 1/2ton
    Engine Size:
    350, 350, 350, 350, 350
    ^ x2

    The sound you hear is pretty normal on older vehicles with vacuum brakes. That's just the booster doing it's thing.
     
  4. 75gmck25

    75gmck25 Full Access Member

    Posts:
    1,099
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    713
    Joined:
    Oct 13, 2016
    Location:
    Northern Virginia
    First Name:
    Bruce
    Truck Year:
    1975
    Truck Model:
    K25 Camper Special TH350 NP203
    Engine Size:
    5.7
    The cruise control has a vacuum break/switch on the brake pedal. Positive mechanical cutoff for the cruise control servo if you step on the brakes, since it cuts off vacuum to the servo.

    Bruce
     

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