Peterbilt ABS Valve Modulator LEAK

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by LivingstonTruckingLLC, Apr 19, 2026 at 9:39 PM.

  1. Apr 19, 2026 at 9:39 PM #1
    LivingstonTruckingLLC

    LivingstonTruckingLLC Bobtail Member

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    I have a 2010 Pete 388 Tri axle.

    I have an air leak from the ABS Modulator, it only leaks when service brake is applied.

    Coming directly from the bolt I have circled in the yellow, Should I replace the whole ABS Modulator or could it be something else back feeding?

    New to being an Owner/Op so all tips will be appreciated.
     

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    LivingstonTruckingLLC, Apr 19, 2026 at 9:39 PM
    LivingstonTruckingLLC, Apr 19, 2026 at 9:39 PM
    #1
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  3. Apr 19, 2026 at 10:03 PM #2
    Big Road Skateboard

    Big Road Skateboard Road Train Member

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    It can't really leak around the bolt, so either that gasket has failed, or it's cracked on the modulator or valve.

    Unbolt it and see, if it needs a gasket, make one.
     
    Big Road Skateboard, Apr 19, 2026 at 10:03 PM
    Big Road Skateboard, Apr 19, 2026 at 10:03 PM
    #2
    Star Rider, LivingstonTruckingLLC, JB7 and 1 other person Thank this.
  4. Apr 19, 2026 at 10:12 PM #3
    JB7

    JB7 Road Train Member

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    A good rule to go by is if a valve is leaking when the parking brake is off and the foot or hand brake is NOT applied then the leaking valve is not bad. One example would be a relay valve leaking because of a bad brake chamber. Another would be if a foot valve is leaking because of a bad relay valve. See short video attached. Bing Videos
    If a valve is leaking with the brakes applied then that valve is very likely bad.
    I would clean off the leaking area and check for any cracks. Also try to tighten the bolts to make sure none are loose. If that does not solve the problem I would replace the valve.
     
    JB7, Apr 19, 2026 at 10:12 PM
    JB7, Apr 19, 2026 at 10:12 PM
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    Star Rider and LivingstonTruckingLLC Thank this.
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