MACH I Member
Joined: Nov 2006
I sense some confusion between the distribution valve and the proportioning valve. On a car with all drum brakes a proportioning valve isn't used. This is only required on a disc brake system or a disc/drum system. It regulates the amount of hydraulic pressure that is applied to the front verses the rear. A combination valve has both valves incorporated into one unit.
On a dual braking system, there will be a small spool inside of the dist. valve that gets pushed to the side with the lesser pressure (because of a system leak) and the spool then blocks that end off. The spool at the same time pushes on a pin built into a nylon electrical switch that is screwed into the valve. When this happens it completes a ground circuit that lights a brake failure bulb in the instrument cluster.
On a car that has a front and rear drum sys. (manual or power), only a distribution valve is used or needed, as said. It is there to block off either the front or rear hydraulics if a leak is present (dual brake sys) and obviously, to provide a path for the brake fluid. It doesn't affect any pressure. The pressure differential needed between the front and rear, with drums, is controlled by the difference in the wheel cyl piston size and master cyl piston size as determined by the factory.
Any 67 and up to about 1970 and maybe later, Ford vehicle with a drum front brake should have the same separate dist. valve and not a combination valve. There is a difference in the mentioned small nylon electrical switch that mounts to the valve on a 67 (67 only). It only has one electrical prong where from 68 and up it has two prongs. All you need to do is to swap the switch over to the one that you have on your 68, so that the connector will attach. This switch activates the brake failure light on the dash, again as mentioned.
When searching for a used valve, try to find one that still has the lines attached. I have found some valves that have had the lines removed and were exposed to moisture. The moisture seized the spool in the valve block. The way that the valve is designed makes it impossible to use any tool to remove the spool for cleaning and if it can't be pushed out using compressed air, you wouldn't want to use it anyway.