There’s not enough brake boost
I have a 1946 Ford convertible that has been redone mechanically with a 350 Chevy block, 350 Turbo automatic transmission, Mustang II front end, and so on.
The problem I’m having is with the brakes. The power brake booster is located under the driver floor pan and is apparently too small to provide continual power boost.
There are times when you almost need to “stand” on the brake pedal to stop the car quickly. (I’ve never actually tried a panic stop.) Before my mechanic closed shop he had mentioned a duplicate booster, but said it probably wouldn’t help. He also removed the emergency brake system, which I discovered later, (don’t ask).
Is there any solution you have for the brakes and how difficult would it be to put back the emergency brake system?
I think there are two different considerations here.
If the booster is providing sufficient stopping force when the brake pedal is first applied but the assist quickly tapers off, or if there is enough stopping power when the brakes are applied for the first time but insufficient assist during closely spaced subsequent brake applications, then the problem is likely to be with the vacuum supply to the booster and not the booster itself.
If there is not enough volume of vacuum then the booster will not do its job during closely spaced repeated brake applications. Insufficient vacuum is normally caused by a vacuum leak somewhere or an engine that doesn’t produce enough vacuum to begin with. The latter most often results from a radical cam profile or excessive internal wear.
If the vacuum supply to the booster is good but the power assist is still inadequate then the booster is probably undersized and the fix is the installation of a larger booster.
Keep in mind, however, that the problem could possibly be elsewhere in the braking system. For example, the master cylinder could be undersized or the pedal linkage geometry could be wrong.
I can’t say for certain how difficult it will be to reinstall the emergency brake system because I have no idea what system was in your car and what parts were removed. Even in the worst case scenario, however, it is not a prohibitively large project to install an emergency brake setup.