So I was driving in my '79 b3l0 the other day and I was just about to pull into my driveway, when I heard a loud pop from the rear of the car, almost like it backfired. After that happened, the brakes in my car got progressivly worse over the course of about two days. At the time, my alternator was also starting to go out, so I figured it had something to do with that. Well, i changed the alternator (after a friend told me the breaking problem had nothing to do with the alternator) and, of course, the brakes were still bad. I filled up the master cylinder with brake fluid (it was pretty low)and it didnt change anything.
Here are some symptoms: One: I have to practically stand on the brake to get the car to stop. Two: The engine seems to struggle when I press the brake down. I dont know much about brakes so i'm not sure what the solution is here. Do I have a leak in the break line? Does anyone have ideas?

1. could be low brake pads

2. air in the line if u were running the cylinder low

3. ur going to fast for drums to pull up haha

4. brakes glazed


there my opiinions.. i dnt no much either on brakes

When the pop happened, did the brake pedal change / shudder / jump?

Are there any signs of fluid leaking from any of the wheels?

Do you have a vacuum booster fitted to the master cylinder?

Is the pedal firm or soft?

Sounds like the booster is dead.

To check, plug the hose to the manifold. This should stop the engine from stalling.

Options?

New booster or diaphram for the booster.

You could always go for a smaller master cylinder and delete the booster. . .

booster or check valve.

Why use a smaller MC or remove booster?

Nothing really happened when I heard the pop. The brakes were still fine until the next day. they only started to get really bad by the second day. I havent seen any fluid leaking except a small amount under the diff but that could be something else. I do have a "master vac" hooked up to the master cylinder. I'm not sure if that's the same thing. The pedal is very firm.

Also, i was only going about 20 mph when this happened.

Your master cylinder leak will be internal ie. straight into the booster. Just get another master cyl and booster or yours reconditioned although the boosters are quite expensive to replace so recondtioning would be the best way.

One more thing, if it is the booster/master vac, can it be fixed? If so how do I do that? I know they have them at NAPA for $130 but i'm broke. I have a friend who is a mechanic that can help me if the booster is the culprit.

Master cyl is easy, thats just a seal kit that costs about $20AU. As for the booster I wouldnt have a clue as 1200's here dont have them and I never bothered fitting one (built calf muscles from hell with my new brakes).