I just went back and looked at your first post. If you installed a Haldex 103081X modulating valve, you probably don't have the system to support it. The purpose of this particular valve is to divert air from the service chambers and apply the spring brakes if the service brakes fail. I'm sure you don't have a system that sophisticated on a 50 something year old truck. All you need is an R12 relay valve and a quick release for your spring brakes. How did you wind up with a Haldex modulating valve anyway?

If you have a valve with a port on top and a port on each side and an exhaust at the bottom mounted on the back cross member, it is probably a quick release valve.

http://www.finditparts.com/products...564&gclid=CJWTpMKp8sQCFQioaQodY0IAdg

They come in plastic or pot metal. Trying to match them up by looks can be deceiving. Manufacturers are always changing the looks of the valves. You need to by them by what they need to do.

If you have a valve with a small line going to the treadle valve, a big line going to an air tank and a line to the air chambers at the port closest to the slack adjuster that is leaking, you need an R12 Valve. They come in all shapes and sizes, but the function is the same. On this particular one, the small port on top would go to your treadle valve, the larger port on the side to an air tank and two on the bottom to your chambers and two would be plugged.

http://www.amazon.com/Bendix-Style-Vertical-Delivery-102626/dp/B005458HWE

Most of them come with 4 service ports for a tandem rear. With a single axle, you simply plug two of the ports.