strange braking issue

[Warwick5s]

For the last few months my brakes have been acting strangely. It seems like one day, they'll be fine - very firm, easy to modulate, and powerful. And then the next day, they're mushy beyond belief, and the pedal will go almost all the way to the floor before i get any brakes - and then when i do get brakes they lock up, kinda like how abs feels when your wheels lock and the pedal dives to the floor. sometimes when they're mushy if i pump the brake pedal a few times my brakes will get better, but sometimes they don't.


if it was that mushy all the time i'd suspect master cylinder, but since it's so freaking random i'm kind of at a loss. it's a stock 90 S13 without ABS. i have bled the brakes and changed brake fluid within the past 6 months.


anyone have any ideas? brake booster maybe? i've checked all the vacuum lines and they are all intact.

[onboost]

does it happen more when the weather is hot outside??

try stop the car, push the brake padel all the way down to the floor, and hold it there very firmly. see if the padel slowly sinks down.

[Rennen]

How is your brake fluid level now?

I had a leak in one of my rear calipers and had similar symptoms. What would happen is that when I would let the car sit, brake fluid would drain out of line, leaving a bunch of air in there, then when I would drive around it would sort of self bleed because I was pushing the brakes, and that would run fluid down the line and push the air out. This way the pedal was semi-firm when I had driven it recently, but super mushy when I let it sit for a while. The easiest way to tell is to check your MC fluid level often, rather than crawl around under the car looking for leaks. Oh, and make sure all of your bleeder valves are closed tightly if you just bled them recently. Anyway, I replaced both my rear calipers, switched to SS brake lines, bled the system, and now its all good.

-Matt