Brake Master cylinder.

Reservoir is integral to master cylinder so no.

This is the old one that has been binned and replaced with a recon unit but it shows what I mean anyway.

Spent all day today trying to get this working and baffled 4 experienced mechanics.

Basicly with it off the car if you press the plunger with a finger over the outlet you pressure as you would expect but as soon as you release the plunger you get a strong vaccum against your finger and it will not pull from the reservior.

I've had this and the old one apart and really cant see anything obviously wrong. All the seals look good and the bore is spotless. Although I did do an experiment awhich did make it work but wouldn't want to fit it to the car like it.

Basicly I removed the front seal leaving the rear main seal in place and pressed it then. That gave a reasonable squirt of fluid. But of course if there had been any pressure against it would have just gone back into the reservior. What this did do was confirm that the front seal is not letting go to allow fluid in from the reservior. So a new experiment was done. A small washer (a wrap round of welding wire) .6mm in width was fitted to effectively shorten the actuating rod. This caused the master to work as it should. But I really don't like this as a long term solution in case it came undone and tore a seal or jammed the piston. This also slipped out of place after a few uses causing it to fail again.

Basicly it seems that the rod is slightly to long and thus is always holding the seal against the inlet.

Making a diagram now to try and make what I'm saying a bit clearer.

Success!!!

It works again