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JANECZFJ
JANECZFJ, District Service Manager
Category: Heavy Equipment
Satisfied Customers: 241
Experience:  Recently retired District Service Manager for major supplier of HD drivetrain & brakes.
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I have a 1985 Volvo White Truck with air leaking from the Trailer

Customer Question

I have a 1985 Volvo White Truck with air leaking from the Trailer parking brake air supply valve (RED one) on the dash. It leaks whenever both the tractor and trailer parking brake valves are not both relased (pushed in). If just the trailer parking brake valve is pushed in(disengaged) and the tractor parking brake valve is engaged(pulled out) air is rushing out of the trailer parking brake valve. If the trailer parking brake valve is pulled out (engaged) and the tractor parking brake valve is disengaged (pushed in) air is also rushing out of the trailer parking brake valve. The only time air stops rushing is whenever both valves are pushed in. I have replaced both valves at the dash and the one large "relay?" vavle that feeds the gladhands. What could be the cause of this?
Submitted: 5 years ago.
Category: Heavy Equipment
Expert:  JANECZFJ replied 5 years ago.

JANECZFJ :

Hello my name is Frank and I am here to assist you. The air is coming out of the exhaust port. When the valves are pulled out no air goes to the trailer supply line and no air goes to the park brake on the tractor. In this state the exhaust ports are open on both valves and any air feeding back from some where else will leak out the exhaust. To trouble shoot with the valves in the applied position ( buttons out) pull the delivery lines from each valve one at a time. There should be no air coming back . If it does it could be a bad two way check valve that controls primary and secondary air that supplies the valve or a bad tractor protection feeding back. Start with these checks and reply back to me if you need more assistance.

JACUSTOMER-jvc4kpux- :

Thanks for your reply. So with both of the buttons out and system pressurized just pick one of the valves and remove the line attached to the delivery port of the valve? And if the first one I pick does not have any air coming out of the disconnected line then reconnect and check the next one to isolate the feed back? Am I checking for air coming from the line or the port where I removed the line from the valve?

Expert:  JANECZFJ replied 5 years ago.
You are checking for air coming back from the line.