Calling 4070B guru’s!!!

‘77 4070B, dog leg and brake release valves. Hooked the truck to my hopper bottom trailer and it won’t release just the trailer brakes. Both truck and trailer have to be released. I can’t imagine them not working independently. When I try to apply the dog leg, alot of air is released from the valve under the brake pedal. I swapped that valve with another, from my ‘78 4070B parts truck and it did the same thing. Checked another 4070, and the valve release air from the bottom also. Really got me scratching my head.

 

I rerouted the lines and they now come out under the cab, directly below the air manifold, that is accessible through the small door on the left side of the bunk. I routed the lines through the floor, then towards the front by the steering box, then down the frame rail and up towards quick couplers at the headache rack. I did this so that the lines would never have to be released, if I lift the cab.
A few guys have told me, “that just how those old Binders are”. I’m having a hard time believing that both, truck and trailer have to be released at the same time and not independently. This is pretty crucial cause I’m wanting to use this truck on a frameless end dump trailer, where I can lock either or, while dumping.