Unless you see fluid leaking at one of the wheel cyls or at a brake line, the M/C must be at fault.
Scored bore or piston seals that don't seal properly will allow fluid to "leak" past the seals internally as pressure is applied.
Speedy Jim
How much ware in the master cylinder will cause the pedal to slowly disappear ?
I have replaced all wheel C's, I stripped the MC, there was a bit of scoring but not much .
I filled the system today with dot 4 and bled 4 lines.
I had poor results. I can get a reasonable pedal but it 'disappears if you hold it down for a few seconds. I suspect the MC, as all else is new. Is 'any' wear unacceptable or should I be checking some where else 1st ?
I have never rebuilt a complete system..
Rich
Not sure if your car would have it or not.... But have you checked the balancing valve? It's entirely possible that this could be at fault. Had one go on one of my old VW's and it was a SOB to figure out.
My dad's '66 beetle once had a similar problem, it was a leaking brake line (not sure this is the name), the long metallic tube that takes brake fluid from the front of the car to the back.
Joseph Mpora
Thank you all. A fresh look today and I solved it.
It urned out to be a tiny leak at the T junction at the back. Tweaked it a little tighter and now all is well :-)
I had replaced all the brake lines and didnt want to 'over' tighten them. I am still amazed at how little fluid is needed to leak to cause the loss of pedal. - I was looking for a much bigger problem, so I missed the little leak !
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