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Was it Winston Churchill who said....... 'Never in the field of human conquest have good braking systems been replaced with no so good braking systems....

Check out the friction coefficient of the brake pads. If you have 'race' type pads, they might not bite until they get really hot. Not good for street use.

There is no real braking action [ enough pressure applied to start retardation ] until all four shoes/disc pads come up against resistance. It is not just the rear brake shoes.

Prod length is not going to have any appreciable effect on braking force. You need to check a couple of things: - M/c bore is correct for that disc/drum combo - the p/rod is in the correct position on the pedal. For power brakes it will be the lower hole if it has two holes. If above is...

Just for typing.........

Your 50+ yr brake lines may well have rusted internally or built up sediment that is compromising the brakes.

JYH, You could be right but here in OZ around 1974, Chrys started using a short, stubby alum m/c with the booster....but kept the brace. It was also a single diaphragm booster, so not much sticking out....

JY Hero, The m/c is a sol lump of metal, & a manual m/c bolts direct onto the pedal assy. It is as rigid as it can be. The m/c for power brakes bolts onto a balloon/round structure made of sheet metal. That has some flex in it, not rigid.

It is NOT the extra weight of a cast iron m/cl that the brace is reqd. The difference in weight between a CI & an alum m/c would be lucky to be 4 lbs...... That is nothing compared to the force of you number 12s on the brake pedal..... That is what the brace is for.....

Could those be Imperial drums?

I would install the brace. It reduces flexing when the brakes are applied. Without the braces, the pedal will not have as solid a feel as it would with the braces. A nice, solid brake pedal is always re-assuring......especially when that semi looms up ahead......

If you had return springs missing & other bits in the rear brakes, it could allow the brake shoes to rub on the drums. That would heat the shoes up veeeery quickly & make them 'grabby'.....

I do not see any mention of braking co-efficient. The friction co-efficient of the pads & shoes. They are available in different materials that changes the brake feel...& the amount of force to generate braking.

Soooooooooo, the Val & Cuda are about the same weight....so you would find the m/c size that was used on the 68 Val.....& get one that size. When discs are used with drums, a proportioning valve is need to reduce pressure to the drums.....because discs require about 50% more line pressure than...

Any update?

Summit sent you a bad booster...or check valve is defective.

My comments assume the brake booster is correct for the application. The OP states that the pedal travel is normal 1" or so [ post #3 ] & pedal is 'rock hard '. That tells you: no air in the system. So how can it be lack of travel??? Using that 'logic', you would not be able to bleed the brakes...

Don't know how many times I have to say it: brake booster [ BB]. Based on the symptoms described in post #1. Booster operation is quite complicated. Modern boosters are vacuum suspended, ie at rest both sides of the diaphragm inside are balanced by engine vacuum. When the pedal is moved...

^^^^ This. It boils down to: if some pressure [ light pedal ] is good......then more pressure [ harder on the pedal ] should be better. Except in your case it is not......

Dartman, Read post #14. Given the accurate & detailed description of the problem you outlined, I am simply amazed at some of the illogical suggestions [ such as p'rod adjustment when you clearly stated that the brakes start applying with 1" of pedal movement ]. Other than a defective booster...

This sounds like a booster problem. The booster has internal valving to modulate the line/output pressure, which I suspect is faulty. Low pressure on pedal=low output pressure; higher pedal pressure= higher pressure.

Donate it to your favourite junk pile.

Is the inner seal binding?

There is no problem connecting the booster hose to an individual runner. I have owned Chrys cars that used that system.

Take the car for a drive until the brakes pull. stop & put your hand on each front drum. The 'pull' side [ the right ] will probably be hotter. That means the shoes are rubbing building up heat & changing the friction co-efficient. Could be adjustment, soft return springs, out of round drum...

The shoes maybe for oversize drums, & your drums still standard size [ not machined? ]. The shoe material near the yw spring does look quite thick, but only a pic.

The attachment point for the m/c rod is very close to the pedal pivot. On purpose. Because it gives the necessary leverage with manual [ non-power] brakes. It also means the m/c rod travels less distance. I suspect the distance off the floor might be correct to allow enough travel of the rod...

One of the problems with bleeding brakes in old cars is this. Detroit used their wonder metal, cast iron, for a lot of m/cyls. They rust from moisture absorbed, build up a rust pile in the mcl. When you bleed the brakes, bottoming the pistons in the mcl, seals get ripped when they pass over the...

The bore size of the dual m/c needs to be the same size as the single m/c. So that can be measured or obtained from a service manual. According to my Motors Manual 1960-64 Ply Val used a 1" bore m/c. No proportioning valve needed. With drum brakes, 'proportioning' is done with the wheel cyl...

^^^^^This. Hoses can block up with sediment over the years.