my brakes grabs but then get soft.. master cylinder or brake booster?

please help me i need to get this fixed asap!

master cylinder. mine did same thing when it went bad. make sure you get either a OEM one or go to advanced auto parts. trust me, do not go to auto zone for brake stuff. they suck!

AIM: AugieD Z88

try bleeding your brakes before you do this… you never know, it might just be a little air in your brake lines. that happenned to me