Air brake/leak question at tractor protection valve on a 1990 379

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by 260REM, Jul 29, 2026.

  1. Jul 29, 2026 #1
    260REM

    260REM Bobtail Member

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    Aug 9, 2023
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    I have been tracking down air leaks on a 1990 379. While replacing air actuators on hvac system I hit the trailer brake release valve. The glad hands were connected to each other at the time and I now have a big leak at the tractor protection valve under the cab and my brake application gauge is showing 60 lbs.
    Did I back feed through lines and damage TPV ? Or could I have damaged something else like the brake/treadle valve?
    Also have an mv-2 valve, can I convert to a mv-3 valve? If so is it a direct swap or is there more to it?
    Thanks.
     
    Last edited: Jul 29, 2026
    260REM, Jul 29, 2026
    260REM, Jul 29, 2026
    #1
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  3. Jul 30, 2026 #2
    Raffito

    Raffito Light Load Member

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    Aug 25, 2019
    Ingram, TX
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    Make sure you didn't push the valve in. If it's not, you may have damage an o'ring. Air is just back feed from red hose to the blue hose and through the TPV exhaust port.
    MV-3 should be a direct swap, make sure to mark all the hose before taking them off.
     
    Raffito, Jul 30, 2026
    Raffito, Jul 30, 2026
    #2
    260REM Thanks this.
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