Hi guys: I finally drove my 69 Hemi bird for the first time in this decade, and,apart for the general driving experience, one thing became very clear, that as soon I touch the brake pedal, the brake lock very quickly, to the point that they scare me to death! I have power disc brakes, now I wander if there is a way to make them less sensitive to my right foot. I really appreciate any advice on this matter! Thank you.

It may be that you just have to get used to the brake pedal pressure you apply.

Douse it have disc brakes on all 4 or drum in back?

cap the vacuum line to the booster and see if it still does it.
it will be harder to brake in general, but if they are grabby because of the booster, it will stop.

there is an internal valve inside, that is supposed to be gradual, but if it is sticky you get what feels like you are slamming on the brakes once it breaks loose inside.

without the assist it would be gradual once you bleed off all the stored vacuum pumping the pedal a few times.

What Andrewh said, this will isolate the problem

Guys: thank you for your answers. Now, I have front discs, drums in the back. Another thought: the little valve that goes into the booster has an additional port, in line with the normal one, that is capped by a rubber plug. What if I remove the plug and so have less assist in. the system? Might be worth a try.

I might suggest you pull the master cylinder off the booster, and add one flat washer per stud, then replace the master and tighten the bolts. Test drive the car someplace very open, very slowly, and check the brakes to see if they are better. You will need to push the pedal farther down then before, and the brakes won't grab as quickly, so be prepared. If the brakes function better, then remove the master cylinder, and remove the washers. You will need to adjust the length of the rod between the master and the booster.

The little rod between the booster and the master cylinder is suppose to have an adjustment on it. That adjustment is to adjust for slightly different depths of the master cylinder piston. If the brakes grab too fast, the rod length is probably too long. If the pedal seems to travel a long way before the brakes begin to apply, the rod length is probably too short. The threads on the end are fine thread, and a very little movement makes a huge difference. A full revolution to shorten the length of that end could result in no brake application at all!

The rod has a small threaded end with a lock nut on it. Loosen the lock nut, and turn the end in one 1/4 turn, then tighten the lock nut. Do not go more than a 1/4 turn at a time (you don't have to turn the end a 1/4 turn, but its a good starting point). A 1/4 turn makes a pretty big difference. Turning the end in gives you more pedal movement before the brakes are applied, if you turn the end out, it applies the brakes quicker.

Once the adjustment has been made, reinstall the master (without the extra washers) and test the brakes. If farther adjustments are required, its only a matter of removing the nuts that hold the master to the booster and adjusting the rod length as needed, then reinstall the master. If you want to play with the adjustment a bit, you can get the brakes to apply when you want them to. Gene

if you unplug that plugged port all you will do is give yourself a vacuum leak.
it won't affect the booster, because overall vacuum would be the same.

the spacing issue, would be more of always partiallly engaged or you feel dragging, and hot brakes, not sudden stopping.

Not a B body guy, but it almost sounds like a manual pedal assembly on a power setup. Not even sure if that is possible on a B.

I'm guessing it is your rear brakes that lock up first. That's normal for a factory Mopar brake system. If it is your front discs, you have something else going on at he booster/master cylinder as mentioned above. A larger bore master cylinder will reduce the rate or slope of the initial brake pressure, a smaller bore will steepen the rate of pressure increase.

As mentioned above, the master cylinder rod adjustment is critical. Its a bit of a pain to take it out and adjust it, but the time doing so is well spent. This era of Mopars tend to lock up the rear brakes way to early, especially on a panic stop. Drum brakes are "self-energizing" by design when applied. The brake shoes on them essentially wedge towards the brake drum once they start touching it and that wedging effect increases the total force of the braking at a given wheel.. Adjusting them does help significantly, but there are other "tricks" to reduce the overall braking power the provide once applied such as changing the wheel cylinder bore size, removing a portion of the brake pad(not too much though) and using either a proportioning valve or pressure surge flattening device.

On the surface, It sounds to me like you need a larger bore master cylinder. You can contact Dr Diff to find out which one you can swap out to reduce the rate of braking for a given pedal pressure.
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I replaced a power brake booster in an 87 Ram. The new one had a symptom you are describing. Try to tickle the stop pedal as lightly as possible and all 4 wheels LOCK like someone threw a stick through the spokes. No members, this is not touchy brakes because I'm not used to it.

I brought the booster to a local brake rebuilder. He installed what he called a reaction valve inside the booster. It worked perfectly after this.