Bleeding master cylinder
The fluid geyser I have is on the 1st downwards stroke of the pedal not the return release stroke which is what led me to "air in the master cyl", the pedal does feel good and I have adusted the brakes further than I normally would. Maybe its normal and I just need to find a good quality lid and seal! It might just be me but I don't think "modern" rubber repop seals seem to be as good as the older oe type rubber ones. Any thought on where to buy a decent one?
thanks for your reply
On the down stroke is also normal
That is how the compensating port works. Whenever the pedal parks, it allows the piston in there to return to it's parked position. Fluid pressure in the line relaxes. the cylinder remains full of fluid. When yo press down on the pedal, some of the fluid is forced back out into the reservoir, before the piston passes by the hole and closes the port. In this way that little hole adjusts the fluid volume in the system in "compensation" for the pads and shoes wearing. And it also ensures that in a good working system there is no pressure in the lines when the pedal parks, and thus the brakes cannot remain on.
However,
There may be more here than meets the eye. The geyser on the downstroke, in your case seems excessive. I might suspect that the hole is too large. It does not need to be any larger than 1/32 or .030. If the hole is too small it can rust shut over time.It doesn't hurt to be larger, but larger creates the issue you have, in as much as the geyser is constantly flooding the diaphragm. Also, if the pushrod that depresses the piston is too short, then this also aggravates the situation, as it then has a pretty good speed when it hits the piston, and Wham! the fluid is blasted up out thru the port.
So,IMO, the hole may be too large or the pushrod adjustment is too short, or the pedal is parking too high.
If the mechanicals are 100% ok, then,The most simple solution is to install a deflector over the hole. I have used any old piece of thick plastic that cannot be sucked tight to the hole;problem solved.
