I have a 94 Honda civic and whenever I stop at a red light, the brake pedal slowly sinks down and eventually gets to the floor after a couple minutes. Its stiff other than that, and its definitely not leaking any brake fluid. Any ideas?

 

Replace the master cylinder, it has an internal leak.

 

Replace the master cylinder, it has an internal leak.

It's a pretty easy job too. And when you try to pry the master cylinder off of the booster, make sure you pump the brake a few times with the car off to relieve the pressure.

 

Thanks, I'll try that then. It's the master cylinder even though the fluid level in the reservoir never changes?

 

Yes this is very typical of a worn-out master cylinder. The piston inside has fluid on both sides. One side is at high pressure driving the calipers, and the other side is low pressure basically connected to the reservoir. So as fluid leaks past the piston the pressure decreases, causing the pedal to move down. No fluid is lost to outside though.

This situation will get worse and worse until ultimately it can't build any pressure at all and you won't be able to stop.