[Scarebird]

Originally Posted by chuckies76ta

With this new Booster have you checked your vacuum. I'd be curious to know what the engine vacuum is at idle? Sounds to me like you don't have enough vacuum to run this booster which is your first problem.

Originally Posted by VCho455

With single digit manifold vacuum it's time for a new plan.
Electric vacuum pump with your existing master cylinder or,
Manual brake master cylinder or
A Hydro-boost system.

I am of the opinion that you have more than one problem contributing to your lack luster brakes.

The 77 booster is not up to single digit vacuum. The later dual 9" will go down to 9" easily - maybe lower. A vacuumpump may solve the issue - I ran a manual master on mine and it worked excellent.