Hello! I recently got this 1976 Chevy Scottsdale and the brakes were really spongy.
I replaced the brake booster and master cylinder and then bled the brakes but when I was done the brakes were still spongy.
The vacuum hose going to the booster has good suction so I don't think that's the issue.
Any suggestions would be greatly appreciated!
Most of problems got mentioned, but one. Possibility you have collapsed brake lines. meaning old n brittle but not leaking , YET. if any are showing signs of old age, and you didn't replace them also, after one more try at bleeding, starting with bench bleed, going slowly n positive lines stay in reservoir forcing air bubbles out, moving to furthest away, typically right rear, then left rear,front right, front left, proportioning valve lines, finally master cyl. must keep eye on reservoir not let it get to low, or must start all over, so slowly, peddle must stay down with pressure each stroke, if not, air is entering system somewhere, if you hold peddle hard enough and rubber brake lines are old good chance weak one will blow and give itself up, or watch it expand n contract like a balloon, giving away spongyness, also check wheel cylinders for dampness as this is give away for air bubbles getting sucked back into line. I've always use dbl line bottle on vacuum pump to bleed system. one for fluid other for vacuum pressure so fluid wont get into vac pump, only requires one person thus eliminating pedal movement b4 line is sealed. I'm sure theres many tubers who have videos on procedures . i'd ck lines for age, all of rubber lines, then wheel cylinders n calipers, spray brakekleen to dry up wetness, and just let it sit for day, dampness will showup if there is a minuscule leak, all it takes is tiniest of pin hole , air compresses, brake fluid does not, weak rubber lines expand under hard pressure , good lines do not, flex yes. expand no. good luck and pass on tidbit info if it solves your issue
