Brakes
    critical urgency
    truck
    trailer

    Why Are My Truck Air Brakes Leaking?

    Typical repair cost: $50–$1,500

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    Common Symptoms

    Air pressure drops below 60 PSI
    Compressor runs constantly
    Audible hiss
    Spring brakes apply on their own
    Slow pressure build

    Most Likely Causes

    1

    Worn glad-hand seals

    Cheap and quick fix; check first.

    2

    Cracked air line

    Common at chafe points behind the cab.

    3

    Failed brake chamber diaphragm

    Leak on top of the chamber when service brake applied.

    4

    Failed governor or compressor

    Pressure never builds or governor cycles incorrectly.

    5

    Air dryer purge valve

    Constant hiss from the dryer when system is fully charged.

    How a Shop Diagnoses It

    1. 1.Build full pressure, shut off, time leak rate (DOT spec: ≤2 PSI/min single, ≤3 PSI/min combo).
    2. 2.Soap test all fittings, glad hands, chambers, lines.
    3. 3.Inspect air dryer cycle and purge.

    When to see a professional

    A failing air brake system is an out-of-service violation. Do not move the truck until repaired.

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    Related Brakes problems

    Squealing brakes
    $150–$800 typical repair
    Trailer brake failure
    $50–$1200 typical repair
    Grinding brakes
    $200–$1200 typical repair

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