okay I have a 2004 Buick Rainier which I tried changing the brake pads well I had to change the master cylinder and as that happened as bleed I can after completion of bleeding I end up having a little bit of brakes but then pressure goes away and then it comes back when you let it sit for a while I don't see any leaks or not leaking any fluid but the brakes only work when it sits for a while and builds up loses pressure . however when you do activate the brake it is nice and firm and it feels like it'* on stiff brake but there'* no brake pads in the rotors the rotors are kinda shot

You needed brake pads/rotors,,,,so why did you replace the MC?

Did you bench bleed the MC?

What they said above plus:

How did you bleed the braking system after changing the master cylinder?

Vacuum or pressure bleed?

Order all wheel lines were bled?

Pedal to the floor every time or halfway or . . . ?

There are no brake pads in the rotors??

What'* wrong with them?