Hello! I've been having some issues with my 1997 Ford F-150 XL. It's a 4-Wheel Drive with 4-Wheel ABS, drums in the rear. When i press the brakes, I get no pressure. But after a couple presses, it gains pressure and holds for a few seconds before sinking again. Not to mention, when the brake is pressed and after all outlets are sealed, inside the master cylinder it looks like there is air still going into it when there's no air present. I've been reading forums on the internet and watching videos and it seems it could be my brake pump. However, I want to check with someone has more a little more knowledge than I do. Many thanks!
If the brake lines aren't leaking, then it sounds like a failed master cylinder.
I don't think a failed vacuum booster would cause sinking pedal
