I'm kinda stuck with it for the time being. I bought it last year, so there's no returns on this one!
The only real instructions were on bleeding the master cylinder.
I'll get the proprortining valve sorted out as soon as I can get the skinny on the pedal travel. It's not going anywhere yet. (garage queen)
Looks like I have some internet searching on adjusting power brakes to do! Thanks for the help!

Here is one of the biggest issues with that booster and master cylinder.  My supplier sells those, so I bought one to look it over and would never sell one for sure.  The booster output shaft is designed for a master cylinder having a 1/2" deep engagement depth.  The master cylinder (most, but maybe not all) have a 1" depth.  That said, your pedal has to move the rod 1/2"  before it even engages the master cylinder.  Since the pedal has a ratio of about 6:1, that means the foot contact plate will move 6 times that 1/2", or about 3" before anything even begins to act like brake application.

So, the very first thing to check is the mc engagement depth and the booster output shaft length.  Maybe you will be lucky and the two match up.  Just about all Ford masters ever used on Mustangs have 1" depth, measured from the mounting surface to the bottom of the hole in the master cylinder piston.
Adjusting the rod...  Once you have the booster/master cylinder interface matched up properly, you need to mate the pedal to the rod and to the booster. Simply adjust the rod so the pedal is sitting at its original height.  If it was a properly designed power brake system with a revised pedal ratio, you could set the pedal lower so the car is more comfortable to drive.  With that one, using a manual brake pedal, the travel of the pedal is the same as with manual brakes.  With a revised ratio, the pedal does not need to move as far and can be set lower to the floor, as the final stop will be about the same point.  A revised pedal ratio also gives a much firmer pedal feel.  One of the main reasons why people wind up removing that particular booster is because of a very mushy pedal feel, due to the manual brake pedal directly connected to a power booster.

Check out www.mustangsteve.com/brakes for more info.

The valve that you removed was most likely a combination valve and not solely a metering valve.

Not all disc/drum combination valves have a metering valve but, if the valve included in the kit is the same one I see in many aftermarket kits, it's probably based on a GM combination brake valve. If so, that combination valve would contain 3 functions; metering, pressure differential sensing and proportioning.

The metering valve function would control the front disc brake circuit (it would also be known as a "hold off" valve). Disc brakes react instantly to the input of the brake pedal. Drums do not. The metering valve gives a slight delay to applying the front brakes to allow the rear drum wheel cylinders some time to overcome the tension of the retracting springs and begin moving the brake shoes towards contact of the inner surface of the drums.

The pressure differential valve is warning device. As long as the pressure coming out of the primary and secondary ports of the MC are equal, the pressure differential valve will remain centered. If there's a hydraulic failure in the brake circuit (the rear brakes for example), the pressure on the primary side of the pressure differential valve will be higher than on the secondary side of it. The higher hydraulic force will push the PDV over. This will close the contact of the switch in the combination valve, it will ground the switch circuit and then turn on the brake warning light on the dash (if you have a warning light).

The proportioning valve has a coil spring with a predetermined amount force on the proportional valve to hold it open so normal fluid flow and pressure is directed to the rear brakes. Under normal braking circumstances the proportional valve remains fully open. In the event of a panic stop, brake circuit pressures are very high. This above normal pressure surge overcomes the tension of the spring to compress it. This moves the proportioning valve over to partially block off the combination valve port to the rear brakes, to help reduce the chances of the rear brakes from locking up, or at least help keep them from locking up before the front brakes.

Unless you have a set of brake pressure gauges, turning the knob on a manually adjustable proportioning valve will only be a guess in what it has been set to.

Ford did not use the metering valve.

My 66 had the same feel and i finally fixed it by replacing the long brake line to the rear hose.  There was a very minor leak that did not show up when bled or left sitting. I noticed a little wetness at the fitting. Tightening did not fix it but replacing the brake line did it. The hose was new the long brake line looked ok but was not.  Just a thought.

R5CYA wrote:

MustangSteve wrote:

Ford did not use the metering valve.

Well I certainly would never argue with them!  Thanks!
I have another question. I tried to order the pedal pin relocating kit from Steve and was told that it wouldn't work with the setup I have, as my booster adjustment shaft is not curved to hook up to the relocated pin. at this point I'm looking at two things to try, before either going back to a manual setup or trying to find a used working booster with the correct shaft at the wreckers.

One, I might possibly see about bending the shaft I have. I think this sounds much easier than it is, though. I think it would only work if I can remove the shaft from the booster first. I have no idea if it's doable though.

Two, I might try and make a limiter for the upward movement of the brake pedal, so it's lower and closer to where the brakes start to be applied. No idea if this will work either. I'll need to get someone to get someone to slowly apply the brakes for me while i feel for rod movement on the engine side of the booster. (it's still off from checking if its linkage was adjusted properly last night) I assume that it will probably move as soon as pedal pressure is applied crushing that idea.

any thoughts?
 

These are just my thoughts but, you may be better off just removing the booster you have, sell it and buy the Fox booster/pedal pin setup from MustangSteve.

You would have to disassemble the current booster in order to remove its input rod, as it's affixed to the center of the booster diaphragm inside. If you don't get it reassembled correctly, the booster will likely leak (vacuum).

Bending the input rod of the current booster would drop the eyelet down but, at the same time, doing that is going to make the overall input rod length shorter. This is going to pull the brake pedal even closer to the floor, when connected to the brake pedal pin.