Rightio, thought i'd go through how i rebuilt my master cyl to try and give back some info to this awes forum.
This is my first 'how to' type write-up so please go easy and if anyone has anything to add feel free.
Also, with all these things you follow a 'how to' at your own risk! I won't take responsibilty for anything you do as a result of trying to follow what i have done, after all im no mechanic and could very easily be wrong!!
As a note,
Make sure you have the right kit to suit your cylinder before pulling it apart.
If you are going to grease the new seals only use a specified brake seal silicon grease. My service manual doesnt mention this it just says to coat them with brake fluid before re-assembly, i'll leave that decision to you
I recommend wearing gloves when dealing with brake fluid.
Always take note of how stuff came apart and if needed take pic's.
If using a vice to secure the cylinder always use something to prevent the jaws from damaging the body! The cylinder body is soft and easily damaged.
ONLY USE BRAKE FLUID TO WASH/CLEAN BRAKING COMPONENTS!!
If you feel like this is beyond you many places (repco for one) are able to send a cylinder away to be rebuilt.
So here goes. Set up some room on a bench with a rag down to soak up any excess brake fluid and put your cylinder on it like so
Then undo the fittings holding the reservoir in place (shown by red arrows) and remove the reservoir, take note of any gaskets/washers for when it comes time to re-assemble (there may be crap in there from old fluid so clean all this too)
Now you can undo the fittings where the brake lines connect. This was done because this cylinder is for drums all round and the little black pieces of rubber behind the cones are replaced as part of the kit (i think they're some sort of pressure valve)
Now to get the pistons out you need to push down on the pushrod until it is all the way down, while your doing this you will have to undo the little positioning screw on the underside of the cylinder (may need to crack it first before trying to wrestle with it while you push on the pushrod)
Once thats done pull the rubber cover toward the back of the pushrod exposing the locking washer/circlip. Be careful when removing as the springs in the cylinder will be applying pressure to this clip.
Now the first piston and spring should slide out. You then might have to turn the cylinder up and give it a couple of light taps on the bench to get the second piston and spring to slide down. Once they're out place them alongside the body so you know which one went where.
Once these are out you can inspect the bore of the cylinder. I haven't got any pics of mine as my camera wouldnt let me, but it should look and feel smooth. There should be no gouges or scrape marks up the bore. If there is your probably gonna have to source a new cylinder. Thankfully this one appears to be fine.
Now you have to replace the rubber seals with the ones in your kit. Take note of which way they face before you remove them so they can be replaced the same way as they came out.
I did the first piston first (one on the right) If you turn the piston and spring up and look down the cup on the end of the spring you will see a philips head. This is a long piece of rod with some thread on the end that goes into the piston body. You will need to undo this to get to one of the seals. I compressed the spring with my hand while undoing it so i could feel how much pressure was on it. When it comes time to re-assemble this rod make sure you compress the spring so you can feel that the thread is in properly before you try to tighten it, you can't start this by hand so this is important. You will risk stripping the thread if it is not put back in properly!
The spring, its base, the seal and a thin shim will all now simply pull away. Take note of the seal position/direction and swap it with a new one.
For the other side of the piston i used a small precision screwdriver to lift the old seal and then used my thumb to push it the rest of the way off. Be careful if you use a screwdriver so that you dont score the body of the piston. As with the the other seal make sure you take note of its direction. You should then be able to push the new seal on with your thumb
Now for the second piston.
The spring on this piston is only pressed on to a raised section on the inner shaft. It can be easily pryed off with a small screwdriver as shown. Once thats off you can get to the seal underneath it like the first piston
Then use the same procedure for the remaining two seal as you did for the first piston and that should be it.
Oh and if you do need to soak components or you have to leave them for a while, submerse them in brake fluid to prevent rust
Re-assembly is the opposite of disassembly