A few weeks ago I got in my car after it was parked at the train station and noticed the brake pedal went almost all the way to the floor and the brakes were really weak. This wasn't happening when I drove the car TO the station, only when I started it again which I found strange. The fault light comes on (the exclamation symbol under the park brake symbol) and I limped it to my trusty mechanic who informed me it was the master cylinder. He changed it, and 300 bucks later the prob was gone. At least so I thought, because today I was driving down to Sydney, no probs at all, stopped to fill up, got back in the car and hey presto, the problem's back! it seems really strange that it doesn't come on gradually or even while I'm driving, only when the car has been stopped! are the brakes connected to the computer system at all? and does anyone know how the fault light is triggered? or where the sensor is?

Thanks in advance

Is it losing brake fluid???.....how are the brake hoses????......is the ABS playing up????

the resevoir is almost completely full, and there is no sign of fluid around the discs/wheels. Was hoping to get some ideas before I fork out another $300 for another master cylinder change out

Have you done a vacuum leak test? The booster may not be getting enough vacuum, check the big hose thats going to booster.

Did you take the lid off to check level, or just look at it from outside????.....the rubber seal off the lid will go down with the fluid level, making it look full.
I recommend replacing the brake hoses....they last 10yrs...after that, the performance goes down.....and they detiorate inside too.

Yeah took the cap off and the resevoir is full which would suggest there is no leaks. is replacing the hoses a big job?

Hey guys.
Mabey do a flush & bleed. Mabey when he fitted the mater he didn't bench bleed it properly.
Might have air in the system, also check all the pipe fittings for tightness.
Hope this helps
Cheers Stu

Yup, bleed the lines. And give the mechanic a mouthful of abuse , should have been done properly to start with. Especially when it's to do with brakes. Could be the bleed valves weren't tightened up enough, but that's no comfort to you when you crash into some poor bugger cos your brakes failed.

Also keep checking around your wheels for leaks, I replaced the master cyl on my car a while back and the increase in pressure blew out the wheel (slave) cylinders.

The sensor is situated on the mater cyl and lights up when not in contact with fluid, for example low fluid level or an air bubble in the circuit. Hence why the master cyl is the highest point in the brake circuit.