Air Brake Valve

Hey all, I have a 1994 Ford Areomax L9000. I My MV3 valve is leaking air. I bought a new one and once I got it installed, I push the Tractor brake valve in, then when I push the trailer brake valve in the tractor brake valve pops out. I have it connected the same as the old valve. any help would be greatly appreciated.

 

No It did not do it with the old valve. the secondary air supply port had a plug in it on the old valve and so I did the same thing to the new valve. I ended up putting the old valve back in so I could use the truck. This happened when i did not have the trailer connected. I keep caps on both glad hands when i dont have the trailer hooked up.

 

Well I believe the way the air lines are plumbed the trailer line supplies a valve near the back of the truck and it supplies air to the rear axle also. yes when i push the yellow in it releases the tractor brakes, however on the new valve once i push the red button in the tractor valve pops out. that is why i put the old valve back in