i used a vacuum gauge to measure my 89 7.3 n/a pump. Turns out it topped (bottomed) out at 22" of vacuum. Is this sufficient for this unit? The reason I ask is because I can get 2 good stops on my brakes before it starts to get difficult to depress the brake pedal again. New master cylinder/brake booster , or is this normal? I have everything to do a rear brake job in the future including springs..... let me know your thoughts....... su amigo: mexicanjoe!