Ok, so i have a 87 305 tpi z28 no brake upgrade or anything like that. When i have the car in drive or any moving gear.(anything besides park or neutral) the car will let me push the braks a couple times then it will just die. like i can pump them 3 times and it dies almost everytime. i have drove the car and sometimes it would die while i was holding them at the stop light. How do i fix this? what do i need to check? any help is great thanx