Automotive brake system question...

Last weekend I went to the grocery and the parking lot was almost completely full. I drove past an open spot because it was between two big pickup trucks. After spotting it as I passed, I threw it in reverse and backed into the open space. As I was sitting there still in reverse my car suddenly shot backwards. I instinctively stood on the brake pedal. Hard! Actually my car hadn’t moved at all, it was the truck on my left pulling out that fooled me into thinking I was going backward. So I did my shopping, came out, started the car and the brakes are very mushy. I drove through the parking lot, assessed I could proceed with caution and drove home. The brakes were soft (but functional) all the way back. I assumed the extreme pressure on the brake pedal had popped a brake line or seal in the caliper. I get home, park in the driveway, leave the car for about an hour and sure enough there’s a small pool of brake fluid under the driver side front wheel area. I opened the brake fluid reservoir expecting to find it empty but it was nearly full. I topped it off. When I backed into the garage the brakes seemed normal again. I’ve driven it to work every day since, seems fine no more brake fluid puddles. So here’s the question:
Can very hard pressure on the brake pedal force fluid out of the system without breaking or damaging a seal or line?

My wag, the excessive pressure open up a micro crack somewhere that allowed the juice, the precious juice, to escape. But under normal pressure, the crack is mostly plugged up. I’d still see a mechanic though.

Possibly not important but year and model of car might be relevant.

I would tend to think that you have damaged a seal within the actual brake caliper. It was probably near time-of-life failure anyway and the extreme force you applied to the pedal breached the seal. As long as it continues to work and feel normal to you and as long as fluid loss is negligible,don’t sweat it. You might start saving money for a new set of calipers though.

It’s a 2000 Buick.

Perhaps a little bit of air got into the line near the semi-leak when you took your foot off the pedal. This would replace the lost fluid so the reservoir remained the same level and also cause some mushiness.

I ain’t no mechanic, and I’m confused:
The hard pressure you applied was when you stomped on the brake a couple hours earlier.
The pool of brake fluid accumulated during the hour that the car sat on your driveway, when the hydraulic line was under normal pressure(or none at all).
If a tiny leak happened in the parking lot, why would it continue to leak at home, and then stop leaking?

High pressure, fluid squirts out everywhere. Low pressure, very slow leak plus residual fluid from the squirt drips off the car onto driveway.

Think off a ketchup squirt bottle. There’s always a hole in it, but ketchup only comes out under pressure. But if you squirt it with the cap slightly over it, there’s gonna be a big mess of ketchup that drops off the cap later.

You must have had the brake pads replaced a couple of times, were the calipers replaced too?

Was it a front wheel where the puddle was? The metal brake lines are unlikely to fail but the front brakes have flexible hoses for the last couple of feet, these do fail.

I think you may have pushed some fluid out through a small flaw in either the caliper or the flexible brake lines to the calipers.

Either way you are lucky. You just got a warning. You need a full brake job, pads, calipers, and an inspection of the brake lines.

Picture yourself in a panic stop, where you are traveling fast and you need to jump on the brakes, the small leak is an indication that you could blow out whatever flaw is causing the leak and loose all your brake pressure. This is a very bad situation to contemplate.

As snfaulkner noted I assumed it was sprayed earlier and continued to drip once parked. That’s why the location of a puddle on the ground doesn’t necessarily show where the leak is. It can drip onto a frame rail or a suspension part or something, flow downhill and then drip on the ground somewhere else. The puddle on the ground was somewhere in the vicinity of the front drivers side wheel. When I say puddle I’m talking about maybe a tablespoon of oil. There is a unit with a bunch of brake lines attached which I believe is the anti-lock brake system. It is pretty close to the front wheel also. I’ve looked from the top with a light and didn’t see any problems around there. I need to jack it up to see anything from the bottom.
The car has about 150K on it, I’ve had it since early 2015. I had the brakes worked on about two years ago, don’t recall if the calipers were replaced.

Had a metal brake line pop on my Ranger last summer. They get rusty from road salt around here. When that happened the pedal went soft, stayed soft, fluid reservoir empty, had to replace the line from the junction block to the connection with the flexible hose.

It’s worth noting that modern brake systems are deliberately designed so that a single leak won’t wipe out braking at all four wheels; you’ll either lose both front brakes or both back brakes, but not all four. That said, it’s quite a bit worse to lose the front brakes than it is to lose the back brakes. OP is advised to visit a mechanic in the very near future.

Isn’t it usually split diagonally? So the nearside front shares plumbing with the offside rear and vice versa. This is to avoid the situation where you lose both front brakes.

Preparing to be corrected for the US market, brake hydraulic circuits are normally constructed in a ‘x’ design; if you lose hydraulic on one wheel, you only lose pressure on the other wheel in that circuit (passenger rear + driver front, passenger front + driver rear (or vice versa)). That way you always have one front brake operational (together with the superior force multiplication that that entails).
At any rate, a failure on one of the hydraulic circuits would result in mega pedal travel as the piston within the master cylinder will not be pressurised on the primary or secondary circuit. I’ve worked in the auto industry for 20 years including 10 in workshops repairing these kind of things so when I say ‘F driving that…’ i mean it. You would NOTICE.

In the UK market, GM master cylinders of your vintage had a tendency to ‘flip’ the seal in the master cylinder (usually from over-zealous pumping of the pedal when manual brake bleeding) and a resulting lack of pressure. However, i have also heard of them ‘flipping back’ and being operational again. Maybe this has happened (you describe a sharp braking effort, but that they’re back to normal since then)?

I’d get any leaks thoroughly investigated by a decent auto technician and I would pressure test the system to at least 2 bar pressure. As mentioned previously, flexihoses are a weak point, esp at this age. If still at a loss, isolate all the slave cylinders (calipers) using hose clamps on the flexible hose sections and pressure check on the pedal to see if you can get ‘mushy’ pedal. remove each clamp, retest for mushy pedal and refit, do the next one. If you get ‘mush’ with all calipers clamped, the master cylinder is goosed. If any air (this is what ‘mush’ is, after all) has got into the ABS hydraulic module, there should be a bleed procedure than can be run using a diagnostic computer and will operate the pump and valves to thoroughly purge the system (if my memory serves correctly, at around 2000, GM used a Bosch Teves 6.0 ABS system over here. Buick might have different fitted but all ABS works the same so are likely to have the same functionality).

Brake hydraulics are actually very simple systems so this is easily within the scope of an auto technician (or should be).

Thanks for all the input, everyone. Buick currently parked and I’m driving my truck. I’ll be waiting for a nice weekend day to jack up the Buick and crawl underneath.