Regular readers of this thread might want to sit down, lots of pictures (for me) coming up.
I had noticed that the clutch master I replaced a while back was showing dark fluid.
I flushed it once and it came back, suggesting to me that it was leaking by internally. The past few times I drove it I felt like there was some difficulty changing gears so I decided to finally overhaul the original master and swap them out.
I bought an overhaul kit that last time I was gone from RockAuto:
Tools you need:
It helps to have a vise to use, as there is a circlip holding the master internals in place. I used a Phillip's head screwdriver to put tension on the spring (pushing down) and then removed the circlip using my pliers.
Releasing the tension on the spring should allow you to remove the piston. Mine was a little stuck so I used some needle nose pliers to grab inside the clutch rod recess and pull it out. To get the other pieces out I turned the master upside down and tapped on the side until they came out.
I cleaned out the bore with brake cleaner and then inspected it to make sure there were no grooves etc inside.
Mine was clean so I proceeded. Here's a look at both the old and new internals:
Here's the old and new pistons side by side, you can see how the seal on the old one was flattened:
Assembly is the reverse of disassembly. Use brake fluid to lubricate the seals before putting the internals into the bore. You can't see it in the pictures but there is a brass/copper washer in the new kit, that is to be used as the spacer (I put that into the bore first so the spring wouldn't dig into the bottom which as it turned out was wrong. The washer wouldn't come out when I figured out my mistake so it's still in there. I reused the old nylon washer). You can bench bleed the master if you want (this puts brake fluid inside the bore), I didthe second time around after correcting my mistake. If you don't this will just mean a little longer time to bleed.
Once it's all back together remove the old master. Note if you have cruise then first remove the cruise vacuum actuator, it makes life much easier. You need a flare nut wrench (10mm) to safely remove the hydraulic hard line going to the slave cylinder. I loosened the two 12mm nuts first, then the flare nut. Remember that brake fluid will remove paint so put some protection underneath the hard line (I use a couple of paper towels wadded up). I then removed the nuts completely and finally the hard line. Take care removing the master as there is a gasket underneath its mounting flange. It seems to be thin paper but I didn't have a replacement so I didn't want to bung it up.
Once that is off check inside the hole in the firewall. There is a double wall in that area and a rubber grommet should be in place in the innermost wall. Mine wasn't for some reason, so I pulled it out and sprayed around it with silicone to lubricate it, then put it in place. A little bit of fiddling and you should be able to get it in place.
After that install the overhauled master the reverse of the removal of the old one. Add some brake fluid, bleed the system and you will be good to go. My designated leg was on a school trip so I had to wait for him to get back in order to bleed the system. My wife doesn't buy it when I tell her it's a free workout.