I have a 2007 Honda accord 4cyl. My wife was driving it when the brakes went all the way to the floor. I topped off the reservoir, pumped up the brakes, and the brakes worked fine. A couple of months later it did it again. The fluid was a little low, but not below the min line. This time I can't seem to get the air out of the system. I bled the system per Hondas recommendations but I can't get the system to build pressure. I got decent pressure at the passenger rear, but barely seeping on the other bleeders. I eve cracked the line on master cylinder and tried to bleed it. At a loss here...please help me out. Thanks!

 

Sounds like a problem with the master cylinder.

Was any work done on the car right before the pedal started dropping to the floor?

 

That's a negative. I thought MC too, but that's just a shuttle valve right? My cousin (novice mechanic) thinks it's airlock end in MC or ABS modular.

 

The first time the brakes failed, the resevior was pretty low. Could that have caused the air lock or damage to the MC. Also I can't get the system to build any pressure.

 

Do you have ABS on the car? If so then there is likely air now trapped in the ABS system. The other thing is if the master went dry and air gets trapped in there you will need to bleed the master indipendently first and then bleed the entire system. Bleeding the ABS pump is not something the average driveway mechanic can do without the proper tool.

 

How low was the brake fluid?

If air got into the abs system (not sure if that is possible), that still would not cause your issue.

If the cup seals in the master cylinder are allowing fluid to bypass and not pushing fluid to the brake calipers, then you will have no pressure and the brake pedal will go to the floor.

Your description sounds exactly like a bad master cylinder.

 

If bad master cylinder bad, does it required to be replaced?

 

If a master cylinder is bad, it must be either rebuilt or replaced.