Dual air system help!

the trailer air is supplied by a double check valve, so that it can work from either system. If you have known air pressure in all tanks, figure out which tank feed the system in question and start cracking lines until you find a blockage. is it cold enough where you are to be frozen due to moisture in the lines, if so try adding airbrake anti freeze right after the air dryer (do not run it through the air dryer).

 

Check the pressure at the foot valve, simply take off your suply line on the secondary side of the valve and you should have constant pressure. If not then back trace the line and check at the other end. If you do then take off the delivery line on the other side of the valve and see if anything is coming out when you make a brake application. If you have pressure and nothing is coming out then you need to change the foot valve. If pressure is coming out then go to your quick release valve and do that same thing. Check to see if you have pressure or not.
Your dash gauge will be a seperate issue, most likely a kinked hose bewteen its supply source and the gauge.

 

Trace back the preasure guage hose, and see if there is preasure there, and it is not a bad guage. Check the lines out of the foot valve to the Quick release. then back to the tank, you may have a rivot in the line blocking the air.
In all my years and at one time we use to rebuild our own foot valves I have never seen one work for the rears and not the front, they leak air past not block air.

 

Pull the line going to the brake valve for the front axle. See if somebody put a dime or small flat washer it to block off the air to the brakes. So people did that because they did not like brakes on the steer axle