Power disc brake conversion kit troubles.

Moparmadness408 said

Ok I put a return spring on it, and it appears that the pedal still doesn’t always return like it’s supposed to. The thing is, this engine doesn’t really make enough vacuum for the power brakes to work that well, and for the most part, the car stops very poorly, to the point to where it’s not really safe to drive. And every once in a while the power brakes seem to kind of work, and that’s when I notice the brake pedal not returning properly and the brakes not releasing all the way until I pull up on the pedal.

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Remove the return spring. You don’t need one if the brakes are working properly. So if you think you need one, what you actually need is to fix your brakes still.

It sounds like you may have multiple serious issues. The pushrod for the booster must be the right length, otherwise the brakes will not work properly, can drag, etc. If you have leaks, you need to fix those. And if you don’t make enough vacuum to power the booster, you either need a vacuum reservoir, a vacuum pump, or to remove the booster entirely because you don’t have enough vacuum to run it. With a properly sized master cylinder these cars will stop just fine with manual brakes.