So I usually just drive my 89’ Corvette around town but today I decided to drive it to a town an hour away. My brakes are usually pretty stiff but all of a sudden while driving they got spongy. I had to practically hold the pedal to the floor to brake (brake fluid is full, no leaks) . Then I hit rush hour traffic after driving for 45 minutes. When I came to a stop the car died and the brakes locked up, I couldn’t press the pedal down at all. I put it in park, and it turned back on (I had to press the pedal down to get the engine going again) I drove further down the expressway with no problem. But once I got off and hit that first stop light, brakes locked up/died. It turned on again same as last time. I got to a neighborhood, and came to complete stops at the stop signs, no problem... it stayed running. What the heck is going on???

I did several brake booster tests, and it passed all of them. One mechanic told me it could be bad seals on the master cylinder. Whenever I drive short distances and the brake fluid is still cold it’s thicker so it’s able to block up the bad seal, but once it gets up to operating temp the brake fluid is hotter/thinner it is more easily able to get passed the bad seals causing that spongy Brake feeling. Then once the car cools down the brakes feel normal again. And there is also a wet spot, I’m guessing brake fluid dripping down on a part of the car right below the master cylinder. Brake fluid isn’t low, but I also only had that spongy brake feeling for about 10 minutes.

What would cause it to only happen during long distance drives though? It’s the second time the car has stalled going long distance. But around town it’s fine. And it passed all the brake booster tests.

Turned off the car, pumped the brake pedal until it couldn’t be pumped anymore, kept pressure on the brake pedal, then turned the car on, and the pedal dropped about half an inch or so. The brakes haven’t felt so hard lately. They feel just about right.