First I'll give you a synopsis of what's going on.

About 2 months ago the brakes turned to mush. The fluid in the reservoir vanished.

Replaced the fluid in the master cylinder and the brakes came back for about a month.

About a week ago the brakes lost all pressure again.

Now when I push the brakes they go to the floor and the brake reservoir is still holding the fluid.

There is fluid leaking between the master cylinder and brake booster. It's not a big leak.

My question is - How do I determine where the fault is? I don't want to replace unnecessary parts. Is it the brake booster or master cylinder?

I am an intermediate level experience mechanic and any feedback would greatly be appreciated.
Thanks, PJ

 

Sounds like a bad master and/or booster. Pull the master cyl back and im willing to bet the booster is full of fluid. I had fluid leaking out of the rear of my master cyl and i had a pedal that would drop while holding pressure, i replaced the master and all has been well. Id suggest starting by replacing the master cyl and trying to remove the fluid from the booster, its possible the brake fluid has ruined the diaphram in the booster by now.

 

Motst likely the master. There cheap, replace it.

 

Why would you think it is the booster?
The question above screams beginner. No worries, we all gotta start somewhere.


Replace the Master.