Pulsating air leak when service brake applied

Discussion in 'Freightliner Forum' started by ghalvie, Apr 30, 2020.

  1. ghalvie

    ghalvie Bobtail Member

    9
    2
    Feb 3, 2015
    0
    93 FLD 120. Non abs. Auto slacks (yes that was an option back then). I have an intermittent air leak when I apply the service brakes on the tractor. Occasionally when I apply the brakes, there will be a pulsating whoosh....like I'm repetitively applying and releasing the brakes. I replaced one air can that had a small leak, problem the same.

    Would this be the relay valve not seating correctly? Could it be the proportioning valve? Or could a bad pancake from one of the other cans causing the problem?
    I had a similar issue on an ABS Western Star a few years ago that ended up being the relay valve.

    Any input would be appreciated
     
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  3. x1Heavy

    x1Heavy Road Train Member

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    42,135
    Mar 5, 2016
    White County, Arkansas
    0
    Get a eyeball on your service brake pedal first before anything else. On that floor under your steering wheel.

    IF the service brake pedal valve is whacky then the rest of the truck will literally try to play simon says and the result is probably what you are feeling.
     
    Rideandrepair Thanks this.
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