Master cylinder bleeding

miktt100 wrote: Oh cheers justin, happy christmas mate and I'll bell you this weekend
Have a good day

I will be around Monday onwards.

I read your original description, and it doesn't appear that the master cylinder is working.

There are 2 pistons, and 2 springs. The secondary piston is sprung away from the blind end of the bore, and has a stop bolt through the side of the cylinder wall (otherwise the pistons would just come together and bno fluid could enter the primary circuit.)

With the pedal released, the spring pushes the secondary piston upto the stop, and fluid fills the bore through the pinhole at the blind end.
The primary piston is sprung away from the secondary, so there is a gap between them, and the primary piston hits the circlip at the pedal end of the bore. Fluid now runs into the space between the pistons from the primary feed, through another pinhole.

When you press the pedal, the primary piston slides down the bore, past the pinhole sealing the primary circuit. Fluid can now be pumped out of the primary ports. The spring between the pistons compresses, and the secondary piston moves down the bore, sealing its feed hole, and pushing fluid out of the secondary ports.

Provided the primary piston is pushing in all the way, fluid should pump out of both sets of ports.
In fact, on the bench, fluid should be running out of both sets of ports straight from the reservoir if it has fluid in.

facade wrote: I read your original description, and it doesn't appear that the master cylinder is working.

There are 2 pistons, and 2 springs. The secondary piston is sprung away from the blind end of the bore, and has a stop bolt through the side of the cylinder wall (otherwise the pistons would just come together and bno fluid could enter the primary circuit.)

With the pedal released, the spring pushes the secondary piston upto the stop, and fluid fills the bore through the pinhole at the blind end.
The primary piston is sprung away from the secondary, so there is a gap between them, and the primary piston hits the circlip at the pedal end of the bore. Fluid now runs into the space between the pistons from the primary feed, through another pinhole.

When you press the pedal, the primary piston slides down the bore, past the pinhole sealing the primary circuit. Fluid can now be pumped out of the primary ports. The spring between the pistons compresses, and the secondary piston moves down the bore, sealing its feed hole, and pushing fluid out of the secondary ports.

Provided the primary piston is pushing in all the way, fluid should pump out of both sets of ports.
In fact, on the bench, fluid should be running out of both sets of ports straight from the reservoir if it has fluid in.

That was my thinking when I helped Mike bleed the brakes. The very act of undoing the unions on the MC should mean fluid runs out by gravity alone. The port for the rear did, but the front ports were dry, even with fluid in both reservoir chambers.

GuardianAngel wrote: That was my thinking when I helped Mike bleed the brakes. The very act of undoing the unions on the MC should mean fluid runs out by gravity alone. The port for the rear did, but the front ports were dry, even with fluid in both reservoir chambers.

By front ports, do you mean the ones nearest the servo housing (the primary outlets)?

Only thing I can think of to cause that is primary piston not returning fully towards the open end of the bore so it doesn't clear the inlet pinhole. (or pinhole blocked, I assume it has been cleaned out at rebuild)


With the cylinder dry on the bench, you should be able to blow gently into the fluid inlet, and air will come out of the outlets, (primary inlet to outlet, secondary inlet to outlet individually), and blowing into the primary, or secondary, should not cause air to come out of the other circuit.

The front ports meant the ones furthest from servo , I've cleared all pinholes but if I understand the front piston pushes all the way in and is secured by the bleed screw half way down , because as you look in cylinder when you've screwed the bleed screw in it protrudes into cylinder .

That is a stop screw, the piston should spring back until that screw stops it. This should happen with the inlet pinhole uncovered, so fluid can just run from the reservoir port straight into the bore and then out of the outlets.