Mushy brakes feel after very hard stop

To clarify, the master cylinder can leak internally without leaking externally. It’s a closed cylinder with a piston in it. If fluid leaks past the piston, it still sits in the cylinder- just on the wrong side of the piston. It won’t leak out of the cylinder itself.

True. Thanks for the information.

I’m going to try that pressing hard on the brake test tonight when I get home from work. I take the bus to work now. But will drive more starting Wednesday when I begin a new job.

The brakes smoked and squealed very hard.
I have never had that happen with brakes, It is possible the dealer only checked the outer pads, and there is no guarantee the inner and outer pads wear at the same rate. This is not a dealer only repair find a trusted brake mechanic, and get an estimate! 4mm is getting very low. There are a number of possibilities so I think it is worth a second analysis.

The last time that this happened to any of my cars, it was back in the '70s, with undersized drum brakes. If this happened to a modern car with disc brakes, I would be VERY concerned.
I think that the recommendation to look at–and test–the master cylinder is a very good idea.

I have a mechanic I trust. I can ask him to examine it more closely.

It happened when I had to go from 55mph to zero in a few seconds to avoid an accident

While it’s definitely possible to make modern brakes smoke, generally one hard stop isn’t going to do it. You have to be doing some pretty extended, and illegal, things on the street, or running it pretty hard on the race track to do it.

I’m wondering how cheaply-made your pads are, and if maybe there isn’t a dragging caliper or two that was pre-heating them before your emergency stop.

Yup. I’m not sure about the pads if they are cheaply made or not.

I’m a 52 year old guy who uses my old Corolla for commuting only and errands on weekend. No racing or stuff like that lol

Not sure about a dragging caliper either. Would need to ask a mechanic about that. Thanks!

Several things could cause this symptom, hydraulics, glazed pads, rotors, rotor run-out, etc. The good thing about car brakes is that pretty much every part involved is easily replaced. If all else fails, replacing the master cylinder, pads, rotors, and installing fresh brake fluid will very likely get you back to a car w/ showroom condition braking system. At that point you’ll probably have no brake problem for years. On 12 year old car, that would be a good proactive move given this situation imo. Ask you shop how much that would cost. You might be surprised. The only other problem you might have is the brake booster. So to be complete ask your shop to test its ability to hold vacuum.

Lol. It’s also slightly possible that the brakes aren’t as mushy as I think they are. I had a traumatic feeling when they were smoking and squealed. But it’s important for me to do that brake test and have my trusted mechanic look at it too. Thanks for the reminder that everything in the brake system is replaceable

The smoking and noise is generally from the tires.
If the master cylinder were failing you would likely feel the brake pedal gently drop down while stopped at a traffic light.

Yeah, he’ll be surprised alright, because it’ll be north of 600 bucks.

I’m not generally a fan of prophylactic replacement of parts that aren’t specified in the maintenance schedule. If it’s just his MC that’s bad, and the rotors/pads are fine, there’s no sense paying the extra to replace them.

Yeah because of my tight budget I can only afford to fix what’s necessary. I tried that brake test but couldn’t really tell for sure if there was a difference between hard and fast braking and regular braking as far as mushy.

I noticed maybe some vibration when braking maybe?

Probably the hard stop caused the brake fluid to boil. Releasing air bubbles in the fluid in the wheel calipers.
Have the brakes pressure bled at a qualified shop.

Didn’t know brake fluid could boil! Thanks. Will have it checked.