My car is suffering from a hard brake pedal - but only sometimes! Here's the deal, about 3 months ago I took the car out on a short drive and I ended up sitting still for a while with the car running, in gear with the brake pedal pressed. After about 10 minutes of doing this I was ready to move but the car really hesitated and it felt like I had a flat tire. I was in a area that I couldn't stop for about a mile, and then I got out of the car and looked at the front tires, they were fine but the front right brake was smoking. I pretty much figured out the caliber must be sticking, but I was close to home and figured I could baby it the rest of the way instead of trying to tow it. So I let the car cool for about 20 mins and then I turned the car back on and suddenly everything worked fine - my pedal was back everything was normal. I was going to take it to the shop to have it worked on, but I was leaving on vacation the next day so I couldn't. When I got back I was busy, etc and needless to say I didn't get it looked at.

Anyways, 3 months later and the car has been working fine - no repeats of the problem. However today I was out driving, far away from home and a similar problem happened. All of the sudden, my nice soft, responsive brakes when hard! I still have braking power and I could still accelerate with no problems, but I had a very slight trembling feeling.

Now if I let the brakes cool down, I get my soft brake pedal back. However unlike last time I wasn't close to my home and after driving it about 5 miles the hard brake pedal would come back so I would have to stop and let it cool down - then I could drive another 5 miles or so. I let it cool down each time between 10-30 minutes. The longer I waited, the better the results.

Now with all that said, I searched the forums looking for similar problems but I couldn't find anything. The closet I saw was a bunch of C4's having brake booster problems, but it doesn't happen enough to make me think that's it.

Any ideas would be great. I'm parking it until I take it into the shop next week, but I would like to go in armed with some knowledge.

Thank you,
Chris

 

I forgot to include this, it's a '98 Vette.

 

Were you able to determine what the problem was?
You described the issue I'm currently dealing with, with exact detail.

Any help or reccomendations would be GREATLY appreciated!
Thanks!

 

aside from the master cylinder, there could be a vacuum leak at the booster where it connects to the vacuum hose. You can replace that 90 degree elbow, its a cheap part.

also, the master cylinder over time will kill itself (the seals will leak), thats what I would replace next.

 

There is another thing that can cause a brake to stick and it happened on my tow vehicle truck years ago (a 3500 Chevrolet). An older flexible/rubber brake line can swell internally and act like a check valve. This is the line going from the steel brake line to the caliper which allows the wheel to turn. Depressing the brake will force high pressure fluid into the brake line, increase the internal line size, activate the caliper and cause the brake to work. However once you release the brake petal pressure there is not enough reverse flow/pressure to quickly let the fluid back past this choke point. It will after some time but the brakes will be dragging in the interim. I finally determined this was the only explanation when I raised the offending wheel off the ground and did some testing. Replaces the line and the problem went away. Later did some internet research and found out while not a common issue, it has happened to others.