Squealing noise coming from my brake pedal

After replacing my brake pads and shoes I am hearing a squealing noise coming from the area near my brake pedal. This noise sometimes becomes high pitched if I depress the brake too hard. I am also losing a little bit of brake fluid if I depress the pedal hard several times. The brakes themselves function fine and have no problem stopping. When I bled the brakes today some of the fluid was black. I figured it might be air in the system but after bleeding them it is still happening. I also replaced the bleeder screws.

1997 Pontiac Sunfire 2.4L uses DOT 3 brake fluid.

Oh oh, your car has developed a brake whoopee cushion! I think you may have a leaky seal in the brake master cylinder. When you press on the brake pedal, it squeezes the fluid out, and that could indeed make a squealing noise. Like when you blow up a balloon, then flatten the inlet tube, and let the air out.

Sometimes the seals will get stressed when doing other work on the hydraulic system. The MC seals get put in places they normally don’t ever see, during bleeding for example, and that can tear them if there’s small burr. But squealing? It’s not supposed to do that.

To confirm, look under the dash, at that rod the brake pedal pushes on. Move the carpet away. Do you see any brake fluid accumulating there? There may be a rubber seal you can lift up. Look under that too if you can.

That’s it? Common problem, relatively inexpensive to fix. You’ll need a replacement master cylinder installed for you.

The rod that leads into the brake booster correct? I uploaded a picture of it. Anyhow, theres no brake fluid anywhere near this rod or under the carpet.

Yes, that looks like the rod. No fluid there? Hmm … well my idea is no good. Have to look elsewhere. I suppose it could still be that part that is doing squeaking. Maybe have a friend press on the pedal while you maneuver your ears in that area, might be able to identify what part is doing the squeaking. If so, maybe just a squirt of wd 40 is all that is needed.

It’s more of a squealing sound. When you let air out of a balloon and make it whistle. Except it’s a little more tame than a whistle. it’s definitely not a sound like insufficient lubrication.

hmmm … well, it might be the neoprene diaphragm in the brake booster has sprung a leak. On the other side of the firewall from your photo, inside the engine compartment, look to see if there’s a big flat, roundish thing that sort of looks like a round cake, only turned sideways. If so, that’s the brake booster. It will have a vacuum hose connected it. It harnesses the force of the engine vacuum to make it easier for the driver to push on the brake pedal and stop. Inside that thing is a neoprene diaphragm that isn’t supposed to leak any air from one side to the other. If it did, and the hole was small, it could possibly make a buzzing sound or a whistling sound. And that sound could possibly transfer through the master cylinder to inside the car.

It’s often very difficult to identify where a sound is coming from, b/c of all the other sounds the car is making when the engine is running. Maybe as your mechanic to use an engine stethoscope and use it to probe where the sound is coming from. Sometime I can get good results identifying the source of sounds in my cars just using a length of garden hose.

Be aware that if the brake booster is leaking, it allows unmetered air into the engine. If enough air gets past the leak, it can cause a lean operating condition, which might make the engine tend to overheat, or idle poorly.

I was leaning towards it being the brake booster as well, but just wanted a more educated opinion. I’ll look around and maybe replace the brake booster, and post my results. thanks!