Just posting a problem solved which may help or inspire others: I had magically disappearing brake fluid from my master cylinder, with no visible leak. not much on the ground either. finally traced it down to my slave, where the rod boot was full of fluid.

I debated rebuild vs. replace ($15 difference) but I like the sense of accomplishment of DIY. (no one owns an old car who could afford a newer out of convenience) so i disassembled and sure enough the rubber gasket on the piston had a slice in it. wonder how that could have happened? replaced that with a $7 rebuild kit, cleaned the parts with new brake fluid, and works perfectly. no reason to consume new parts! now the rusty exterior of my slave matches everything else under the hood...

 

Well done.

Slice could have been a split; the rubber does age in there.

 

Welcome - and Thanks for posting! hear lots of problems - not always happy endings/solutions...

Stu Aull
80GS
Alaska

 

glad to see you got the issue sorted out! its always nice to hear that the newer guys here have good working knowledge!

 

I just got an s4 gtu and its doing the same thing. Haven't tried to bleed the brakes yet but the fact that fluid dissapears sounds similar.