Your picture is of a distribution valve, not a proportioning valve. The proportioning valve is an adjustable valve that you plumb into the rear brake line to adjust the pressure going to the rear brakes. If you now have no pressure there, then the shuttle valve has been tripped and moved to close off the rear brakes. There is a procedure to re-center the shuttle, but I can't remember what it is. I do remember when I installed Granada disc brakes on my 68 (disc/drum) I had a similar issue. I tried the re-centering procedure and it didn't work.  I ended up removing the dist. valve and heating it up in an oven to 200 deg. and then slamming it onto a block of wood, I was able to get the stuck shuttle/piston out and clean it up so that I could re-install it, and it moved easily. I re-installed it and was able to dial in the rear brakes pressure and operation. I later replaced it with one out of a 95 once I went to all disc brakes.
*** I looked at your link, and it clarified something for me. My valve in my 68 was like the one in the small photos showing the piston and cut away. The final valve I installed when I did my all disc mod looks like the one in your picture. Sorry if I got it confused - it was done maybe 20 years ago - brain fart.....

Last edited by Ron68 (2/28/2025 2:21 PM)

ACTUALLY…
Your picture is of a combination valve that contains a proportioning valve as well as a differential pressure valve.
The offset of the rear lines IN and OUT tells you it is a disc brake proportioning valve. If the IN and OUT were straight across, it would be for drum brakes and then would only be a differential pressure valve. 

To recenter it, you need to make the end that has the most pressure spring a leak.  Just open a bleed screw on that end, usually a front caliper.  Then go in there snd STOMP on the brake pedal a few times. That will usually move the center spool to the opposite sode or back to center.

MS wrote:

ACTUALLY…
Your picture is of a combination valve that contains a proportioning valve as well as a differential pressure valve.
The offset of the rear lines IN and OUT tells you it is a disc brake proportioning valve. If the IN and OUT were straight across, it would be for drum brakes and then would only be a differential pressure valve.

To recenter it, you need to make the end that has the most pressure spring a leak. Just open a bleed screw on that end, usually a front caliper. Then go in there snd STOMP on the brake pedal a few times. That will usually move the center spool to the opposite sode or back to center.

Thanks for the ACTUALLY MS.
 

The latest on the brake situation:
I installed the new brake pressure distribution valve today but still no pressure (fluid) to the rear brakes. When the brake pedal is depressed, with the rear brake line disconnected at the M/C, there is little fluid squirting from the M/C port. Is it possible that the rod is too short? This is hard to believe because the pedal will go to the floor with the front caliper bleeder valve open. It seems that I may be chasing my tail. 
Any suggestions, gentlemen?

Thanks. This will be the second new M/C that I have put in the car over the last 3 months. It may be the cylinder. Update in a few days.
TM

After all the trials and errors I have experienced on my Falcon's restoration, I still have my self-esteem.
I set the m/c in a vice and proved that it works as it should, i.e. fluid shot from the rear brake port. The rod length is most likely too short. I have ordered the adjustable rod for 1964-1973 Fords.
I just need to set the proper length of the rod to solve this ridiculous issue.
I will report the results over the w/e.

okay. There is no booster involved, btw. The gauges available seem to refer to booster applications. The gap used was .020".

Gentlemen, I am stumped!
Thinking that the problem was due to a M/C pushrod that was too short, I purchased an adjustable rod. It required shortening to fit. Backtracking a bit, I tested the M/C on a vise and fluid from the rear brake bowl shot out as expected. When the M/C is tested in the car, barely a drop dribbles from the rear bowl port.
I installed the new rod and still no fluid comes out of the rear bowl port. The front brakes bleed properly, but I am unable to bleed the rears, since no fluid makes it out of the M/C when it is in the car.
Is it possible to have the rod too long? I have removed the rod from the car in case shortening is recommended.
What might the problem be? Since I checked the operation of the M/C on the bench vise, I thought the problem would be solved with a longer rod or at least with one of the proper length. These are manual brakes, no booster.
The new rod makes contact with the M/C piston, since there is no problem bleeding the front calipers.

 

Yes, if the rod is too long, the piston will not retract and the bowl will not flow fluid into the master cylinder piston bore.
The bowl closest to the firewall feeds front brakes. Bowl closest to radiator is rear brakes.

This may sound a little odd, but did you bleed the front brakes first?  The reason I ask is that I had an issue years ago where I did that on a completely new system (no fluid in the lines to speak of), and it did exactly what you are describing.  It was as if the front system was preventing a decent stroke to move fluid through the rear bowl.  IIRC I fixed it by putting clear vinyl tube on all the bleeders and putting the ends into jars with a little brake fluid in the bottom (to prevent sucking air back through).  I then pumped the pedal like 10 times with all the bleeders open, refilled the fluid, and repeated that another 2 or 3 times.  Then I was able to close all but the farthest bleeder (right rear), and follow a proper bleeding rotation (right rear, left rear, right front, left front) after which everything worked just fine. 

Have you verified the combi valve is centered? It will block flow to the rear if it shifted due to unequal pressure