mackr1989 Posted January 30, 2015 Share Posted January 30, 2015 88 r model leaks air through the gladhands when I hit the brake pedal in the cab. it does this when our trailer is not connected and the trailer brake knob is locked. Quote Link to comment https://www.bigmacktrucks.com/topic/38667-air-leak-from-gladhands/ Share on other sites More sharing options...
gearhead204 Posted January 30, 2015 Share Posted January 30, 2015 sound as if the tractor protection valve is stuck. Buy a new one ! 2 Quote Link to comment https://www.bigmacktrucks.com/topic/38667-air-leak-from-gladhands/#findComment-276643 Share on other sites More sharing options...
Paytonsforit91109 Posted February 6, 2015 Share Posted February 6, 2015 I have the exact same issue on my '74 r795 Quote Link to comment https://www.bigmacktrucks.com/topic/38667-air-leak-from-gladhands/#findComment-277734 Share on other sites More sharing options...
b61mack Posted February 6, 2015 Share Posted February 6, 2015 My 72 R 685 does the same thing, I wonder if it could be a maxi brake leaking back thru. Quote Link to comment https://www.bigmacktrucks.com/topic/38667-air-leak-from-gladhands/#findComment-277754 Share on other sites More sharing options...
gearhead204 Posted February 7, 2015 Share Posted February 7, 2015 a bad maxi should leak as soon as the brakes are released. if it only leaks when the tractor or trailer brakes are applied with out the red knob energized its a faulty tractor protection valve. to test charge trailer and pop the supply glad hand off it should exhaust air until the air tank pressure reaches 60 psi the red knob should pop out, and stop the flow of air. if the knob pops out then step on the treadle valve no air should come out of the glad hand if it does replace the tractor protection valve. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/38667-air-leak-from-gladhands/#findComment-277830 Share on other sites More sharing options...
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