hey guys i just recently replaced all components on my brake system as it was all falling apart. rebuilt calipers, new lines, new master, and new brake booster, etc. Of course there r gonna b a couple leaks for the first time bleeding, but i found 1 between the master and brake booster. i looked it up and they say the master is bad.
what seems strange is that when i bench bled the master there were no leaks. just took it off and no leaks again.
Any ideas why it would only leak when attached to the brake booster?

 

had the same problem with a 4th gen master, either the housing is cracked, or the end seal is bad. Not sure if its serviceable. It wont usually leak until there is pressure in the system, and its a slow leak at that.

if it "only" leaks when on the car, maybe the pressure form the bolts to the booster cause enough distortion to start the leak?

 

yes the leak is only when installed. tried it again after i wrote the original post. though the same thing maybe the case has a flaw somewhere that the torque only further worsens.
thank you for the help
guess ill b runnin back out to advanced again tomorrow.

 

thats the problem right there. most reman stuff from advance, autobone, ect is total crap from china. I usually use delco parts from Nationals, never had a problem