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Thread: M931a2 tractor unit air loss no air leaks

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    Default M931a2 tractor unit air loss no air leaks

    Hi all andy here from the uk
    got a 1989 m931a2 a rare truck over here in england problem i have with truck is slow loss of air pressure from secondry air tank when driveing truck down the road then the primary tank starts to lose air,no air leaks can be heard,but after stoping truck air pressure builds again with no problems and still no air leaks have checked the pipework to airtanks and its fitted correcty as per the tm

    has anyone got any idea what problem could be

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    4 Star General snowtrac nome's Avatar
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    do a google search for a dot air brake test im betting you have a leak in the parking brake release circut

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    I'm going to assume the air compressor is build back up then dropping as you drive? Or is dropping all the way down? If compressor is build back up driving but you only show a loss driving. But not parked with the brake on , check your spring brake pots for a leak. They have pressure when moving but not parked.
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    Quote Originally Posted by jasonjc View Post
    I'm going to assume the air compressor is build back up then dropping as you drive? Or is dropping all the way down? If compressor is build back up driving but you only show a loss driving. But not parked with the brake on , check your spring brake pots for a leak. They have pressure when moving but not parked.
    truck running, air compressor working ok, air pressure dropping all the way down starting to lock up brakes takes about 8 mins or so, then stop truck air then builds up as normal with air leaks detected

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    i 've seen that in civvy tractors. try " jabbing " the truddle valve," foot brake" a few times real quick and see if that fixes it ????
    Beastmaster

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    That sounds to me like a spring brake can leaking to I would also check to see all airbrake lines are closed off I don't think the 5 tons have a trailer brake knob to supply trailer brakes with air. If you preform the dot air brake test you should find the leak in short order.

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    Quote Originally Posted by snowtrac nome View Post
    do a google search for a dot air brake test im betting you have a leak in the parking brake release circut
    This could be a leaking maxi can diaphragm. With parking brake engaged start engine and built to full air. Chock the tires. Then turn off engine. Release the parking brake and then check for air leaks.

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    Default M931a2 tractor unit air loss

    think I have found the problem with the air loss problem I have
    with truck up to temp and full air tanks and the hand brake on,Engine not running I could hear a very faint air leak coming from the air intake stack,Secondry air tank showing air loss. When footbrake was applied very slightly the air leak could not be heard suspect treadle valve to at fault
    anyone else had this problem

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    I'm the dude, man. Steel Soldiers Vendor simp5782's Avatar
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    Quote Originally Posted by camoandy View Post
    think I have found the problem with the air loss problem I have
    with truck up to temp and full air tanks and the hand brake on,Engine not running I could hear a very faint air leak coming from the air intake stack,Secondry air tank showing air loss. When footbrake was applied very slightly the air leak could not be heard suspect treadle valve to at fault
    anyone else had this problem
    Let the parking brake off. the inversion valve on the parking brake bypasses air thru the stack if the o ring is bad and this leaks air out of the stack. Removing the white line off of the bottom side under the cab or whatever line it is in the cab on those small.small lines will tell you if it's that or not
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