Will 'brake' For Beer.

The combination valve on Fords with drum brakes does 2 things. It's a distribution block to send fluid to the front and rear separately, and it's a brake failure warning switch. That's all. If the "shuttle" DOES happen to move and trip the switch that's ALL it does. It doesn't shut off or redirect fluid flow like a GM switch will, so you can eliminate that.

The first thing to suspect is that there is a power brake pedal installed. Yes, there were 2 different pedals, one for power brakes and one for manual brakes. The attachment point is in a different place and if you use a power brake pedal in a manual brake application the pedal effort will be, well, like a power brake without any vacuum.

The next thing to suspect is incorrectly installed shoes. There is a primary shoe and a secondary shoe. You want the primary shoe facing toward the front of the car and the secondary shoe facing the rear. The primary show is the one with the shorter lining.

The next thing is brake shoes with crappy friction (lining) material. Some overseas stuff doesn't generate enough friction to stop a shopping cart. You need shoes with "bite".

The last thing I can think of on the list are brake drums that are close to or past their "discard". Drums that are worn out will provide a small contact area for the shoes, near the center of the lining instead of evenly, all the way around. You can measure the drums with a drum micrometer or gauge.

EDIT: Yep, just looked at your photo's and they look to me like you have the shoes on backwards...longer shoe should be facing the REAR.

In a factory installation, the only Fords that will have a proportioning valve would be one that has discs front/drums rear. Proportioning is only one function of the combination valve. The other function of the combination valve is pressure differential sensing.

These two functions of the disc/drum valve weren't combined into one valve body until 1970. Prior to this (1967-1969), the proportioning valve was external to the pressure differential valve body.

In a 4 wheel drum equipped Mustang, from '67-up, there will only be a pressure differential valve. There is no proportioning valve function in this valve.

Under normal braking situations (disc/drum brake system), the proportioning valve doesn't function. It's only in a panic stop situation, where brake pressure forces are high and there's a dramatic shift in weight of the vehicle from the rear to the front, that the proportioning valve functions to limit the pressure rise to the rear drums, in proportion to the amount of pressure being applied to the front discs.

You can test the brake warning switch of a drum/drum pressure differential valve or a disc/drum combination valve, without removing the plastic switch from the valve body, to determine if the pressure differential valve spool has shifted off center. You can do this by taking a multi-meter and set it for Ohms --even better if you have an audible function on the meter. Touch one lead to the metal prong inside the switch (where the wiring pigtail would plug into the switch). Touch the other meter lead to the outside of the valve body. If you have an audible setting and the meter doesn't 'beep,' then the spool is centered (that's good). If the meter does beep, that's bad because it means the pressure differential valve spool has shifted off-center and the spool will have to be re-centered.

A valve lock tool will only work on a pressure differential valve spool that's centered to begin with --you install it just prior to bleeding the brakes out. It will not re-center a valve spool that previously shifted off-center.

If the flexible brake hoses are old, replace them. The inner lining of them will slough off/collapse over time. This can either make it difficult to get fluid/pressure to the wheel cylinders/caliper pistons or, it can act like a check valve where fluid/pressure builds in the wheel cylinders/caliper pistons but, is slow to release the brakes, once you get off the brake pedal.

The MC bore size can also make a vehicle hard to stop or, make the brakes too sensitive to even lightest brake applications. The smaller the MC bore the higher the output pressure to the brakes but, the less volume of fluid moved. Smaller MC bores will also increase brake pedal travel.

A larger bore MC will have less output pressure but move more fluid. The brake pedal is usually much harder and has less travel. A MC bore that's too large for the brake system will make it difficult to stop the vehicle.

Shoe placement of a drum brake system is important. The shorter shoe goes toward the front. The longer shoe goes toward the rear. If these are swapped, it will make it difficult to stop the car going forward but, it'll stop really well when backing up.

Any oil or grease on the drum linings/disc pads will render them useless and they'll have to be replaced with new components and the friction surfaces of the drums/rotors will have to be thoroughly cleaned before putting the new linings on.

Never take new brakes and immediately start making hard stops with them. This will glaze the linings/pads and friction surfaces of the drums/discs. New brake components have to be bedded in before putting them into regular service or, it will be difficult to get the vehicle to stop. There's plenty of information on the net on how to properly bed in new brakes.

Had the same problem with my 69. Both rear rubber brake lines were blocked. Replaced both and now I have solid brakes.