Opinions please Loosing brake Pressure
 

1994 F-250

So I was driving today and Heard a loud bang, while using the brakes, and then lost constant brake pressure.

I can pump the brakes and they get hard but if i hold the pedal it goes down

I looked at the calipers/drums and found 1 drum that was leaking so I replaced the wheel cylinder and shoes but after bleeding I still have the same symptoms.

I was hoping maybe someone may have had a similar issue, Im leaning towards the brake booster but not sure if theres a way to check it before I buy a new one.

So I just spent the day and replaced the brake booster and Master cylinder and still have the same problem

park the truck over some clean concrete,a nd pump the brakes. sounds like a leaky line possibly.

thanks none of the lines are leaking I did find that the front rotor broke in half

That might do it.