Brake system
 

Need help!!! 94 Mazda B4000le, 2 wheel drive. I just redid my whole brake system front to rear; front has new rotors, calipers, and brake pads. Rear has all new springs, wheel cylinders, and brake shoes. Replaced booster, master cylinder, and new check valve on booster. Within the last couple weeks the brake pedal started getting hard to push down and stop vehicle. I bled the brakes again but still have same problem; I did the booster check according to my Haynes Manual and it passed the check no problem. I live in the mountains in Tennessee so I really need good brakes. When I leave my home and go down the mountain I am damn near standing on brake pedal just to help me slow down but it just keeps rolling. The pedal feels like I don't have the vacuum line hooked up and the pedal tries to push back up against my foot. Please help!

Power brakes use outside air pressure to assist driver in pressing down on the brake pedal

The booster has diaphragm inside, front 1/2 has say -5psi created by engine vacuum, other side is 0psi, when you press down on brake pedal the atmosphere valve opens(inside cab) and 15psi outside pressure rushes in to assist driver in pushing down on the master piston with 20psi pressure

Vacuum is STORED in the booster in case engine should stall, usually you will get 2 or 3 full pedal presses with assist with engine off
So give that a try
Start engine, booster will get -5psi within 10 seconds or less, see if it feels like you have assist
Shut off engine, press brake pedal a few times it should start to get harder after 2nd or 3rd pedal press

If there is no change even with engine running then either new booster is bad or your booster push rod is adjusted wrong

Remove boosters hose from the Engine end, suck on the hose it should HOLD vacuum, so you can't keep sucking on the hose it will build up vacuum, if it doesn't then booster is bad, you are getting no vacuum assist

Remove master from booster(leave brake lines attached), there is an adjustable nut/shaft, press down on brake pedal to make sure it moves freely, if not then there is a problem in the booster
Adjust the nut/shaft so its in all the way, reinstall Master temporarily
See how brake pedal feels, engine off, if there a loose feel at top then you feel it hit master the adjustment was OK, remove master again and reset adjustment
With master off open one bleeder on the front and on bleeder on the rear(you will need to rebleed these
With one bleeder at the front open and one bleeder at the rear open you should be able to push in the Master's piston in fairly easy just has a spring inside, if not then Master is bad