I would like to put my 2nd hand master cylinder but i wouldnt know whether it is going to leak or not so my first question is once i disconnect the brake lines at the cylinder and reconnect them to the new cylinder do i HAVE to bleed the brakes or wont that much air affect it? Because i was thinking that i could take out the old one, put the new one in the reconnect the lines and fill the cylinder and then drive to see if it leaks or not ! (or if its unsafe i can just test in the carport)

Also with the bleeder nipples do i need a certain spanner or will a shifter or a socket do fine?

Oh and is there any difference in flushing brake fluid and bleeding brakes ?

the whole system will need to be bled..
you will find if you just put it on and fill it you will have no or next to no brakes untill all the air is bled out...

Hi go to K Mart or Super Cheap and buy a self bleeder Hose, fill a clean jar half way with brake fluid put the hose in the jar and loosen the nipple till its just open and then put the other end of the bleeder hose on, Open the nipple a little more and whilst the engine is running very gentlly and slowly pump the brake pedal and just repeat this process to all the nipples till their is no more air coming out and you have a firm pedal again. Keep checking the Jar to make sure it doesent overflow.

Its a simple process anyone can do on their own.

And by the time you get round to all the brake lines you would have flushed out most of the old fluid. And no special tool is required to loosen the nipple.

Ive never ran the engine while bleeding brakes?

Never pump the pedal to the floor.
Pump no further than 2/3 to the floor.

Why dont you pump it all the way to the floor? I may need a quick response as i might tackle this in about 30 mins !

You can damage the seals.

The reason you don't let the brake pedal traval all the way to the floor is because, as Madmatt mentioned above, you can damage the seals in the master cylinder. Because the brake pedal doesnt normally use its full travel, the surface of the master cylinder bore is not all used. The area where the seals/piston/cups regularly run is always kept clean and smooth, but the area the piston will run in when the pedal goes to the floor is usually dirty, and may even be pitted/rusted/corroded. The rubber seals will get ripped, and will then leak. You will then need to replace/reco your master cylinder.
The way I always bleed the brakes in a falcon, is to firstly jack the rear of the car as high as possible, to assist the air to get out. Start at the LHR brake, and work your way from LHR, to RHR, then LHF and finally RHF. Have someone in the car to hold pressure on the brake pedal, but have them put there spare foot under the brake pedal. Once the pedal feels firm-ish, have them hold pressure down while you release the LHR bleed nipple. Once the pedal is down, close the nipple and repeat the process until all the air is gone. The move on the the next wheel. Check the master cylinder reservoir between wheels, to make sure it doesnt run dry. If it runs dry, you will have to start all over.
You dont need the engine running to do any of this, the engine is only to supply vacuum to the booster, to make the pedal easier to push.
Make sure and use jack stands, and be careful not to get brake fluid in your eyes, as it can come out with a lot of force. Good luck, and hope this helps.

Gave up today because the hose that came with a kit that i bought from Sprints would not fit over the bleeder nipple ! So i need to find some hose that will actually fit over it !

take the hose that come with the kit to bunnings or local hardware store etc and find a bit of clear hose that tightly slides over the top of the hose from the kit. will probably cost u $1 for a couple of inches

Ah now thats an idea ! Also i was having an issue with my wheel nut removal and i was just wondering if i bleed to brakes with the mags still on and i wash any fluid that spills on it away will it cause any damage to my mags ?

Have a squirty bottle ready with a bit of car wash & water in it.....as soon as it spills, hit it with that.

Mate
If you get some master cylinder pipes from the wreckers and bend them into the reserviors u can bleed the master cylinder before installing. pump the master cylinder piston until there is no bubbles in the reservior. u have bleed the master cylinder. remove the old master cylinder fit the new mastercylinder remove the slave brake pipes loose fit the original brake pipes pump the pedal 6 times and tighten the pipes check pedal. most of the time u will not have to rebleed.

gassa