Brake goes to floor....

[96pathfinder]

Hello all. I'm having problem with 92 Sentra E.

Just the other day, brake light came on when I was driving. Sure enough, brake fluid level was below minimum. At the same time, I realized brake was VERY soft and it went to floor. However, brake worked fine. Just pedal was very soft.

Upon my inspection, I found brake fluid leak at the rear drum (wheel cylinder) So I replaced both wheel cylinders. However, brake pedal is still soft!

I'll try and bleed the brake tomorrow but....Pedal is soft whenever engine is on and if I keep on pumping the pedal, it'll get harder. But if I leave it for few seconds and press the pedal again, it goes to floor again.

I always thought when pedal goes to floor, its a sign of bad master cylinder or booster. What's the sure way to find out either MC or booster is bad?

Any help is appreciated.Thanks!

[RED_DET]

Well after you replaced the rear brakes, you need to bleed the system, you have added air into the system along with the air that was added when it was leaking. That should solve your problem. Start with the wheel farthers away from the master cylinder and work in that order until the last wheel is the closest one.

[96pathfinder]

Thank you for your reply. Yes, it was air in the system that was causing this problem.After I bled the system, everything works fine now.Thanks!