When I lightly brake to slow down, the brake pedal will get lower and lower until my brake failure light came on, but when I release the brake after I stopped and push the pedal hard, it feels fine and the light goes off. I took it to a mechanic and he said it was bad fluid and he flushed the system. It worked fine for a couple of days, but now the problem is worse. Now when I lightly brake, the pedal goes all the way to the floor and the light doesn't come on, but when I brake harder it feels ok. What could cause this?

 

Year and model would help immensely. Still, generally what you describe is a failing brake master cylinder. Should you have an 89+ car w/ ABS, it could be issues there...generally the m/c.

 

It's a '89 240DL without ABS

 

OK...sounds very much like the master cylinder has failed. Not sure how comfortable you are w/ your mechanic....but bad brake fluid does not cause what you're describing in normal city driving. Contaminated fluid is most evident under hard, protracted braking.

 

Thanks. It was the master cylinder. This was not my usual mechanic that flushed my system and I will never recommend this guy to anyone. My husband replaced the master cylinder and when he bled the system, the fluid was BLACK!!! How can a flushed system have black fluid?

 

It can't...you were ripped off!