How?

dont like the easy bleed -just seems complicated.

I can see both sides of this.

Pro :- When I first got the Saab, I changed the brake fluid, which also does the clutch. In the process, I killed the clutch master, because it started to go into parts of the bore it'd not been to for years and buggered the seals.

Con :- The master in Hetty has done maybe a thousand miles tops from new. However, it's been sat around for years with DOT brake fluid in, so there MAY be corrosion. If there is, it's just as likely to be in parts of the bore that the piston may well come into contact with in normal use, killing it quickly anyway. The Saab's clutch master was FOOKED internally - the internal return spring had rusted through and was in about five bits, so it really wasn't any great less to mankind.

Never came for an argument, just to state facts!

still cant see how adding fresh fluid to the reservoir and pumping it through with the pedal will be more detrimental than forcing fluid past the seal using compressed air from the spare.

there was a spate of "dodgy master cylinder" posts on the t'internet forum without pictures a good few years ago

If you simply put fluid in the reservoir of an empty master and try to bleed it through the wheels it can be quite a task to get a good pedal-hence "it must be broken..."advice. I found that by purging the master by disconnecting the unions at the master until fluid flows out it gives a better start to the whole procedure. Somehow air in the pipe and air in the master don't work.

I know it makes no sense - it shouldn't make any difference but I've brought a few masters "back to life" that way.

With respect, that is nonsense. The master cylinder on a properly bled braking system never gets to the bottom of its stroke, or anywhere near it. By pressure bleeding the system you prevent the master cylinder seals from going further down the bore than they normally would.

There are other advantages, small master cylinders don't move enough fluid in one stroke to purge a long brake line and slave cylinder. Pressure bleeding is quicker and makes it easier to completely change the fluid.

How does pressure bleeding "force fluid past the seal"? The seal sits at the beginning of the bore. The brake fluid reservoir, which you pressurise, allows fluid to enter the bore. As you press the pedal the seal moves past the intake hole and the secondary seal on the piston stops the remaining fluid in the reservoir from leaking out of the back of the master.

When you pressure bleed the master cylinder the front seal just sits idly, nothing gets forced past it; if it does the master is well and truly cream crackered.

True.....

Bought a non return valve yesterday and some clear pipe. Instructions say to attache it to the nipple and then pump the brake pedal.

I'll use a bit of wood to stop the pedal going all the way down

Well I can see that Roy removed his very correct statment. When a master cylinder is buggered, it means it is buggered. NEVER save money on brakes, if the MC fails and the pedal finds the floor, you are dead meat. It cost bugger all, stick a new on and relaxe. If it can't handle being bleed and will fail due to corosion don't hesitate one second.

I would certainly replace the master cylinder if it showed any signs at all of not being up to muster.

I bleed the farthest cylinder first yes?