To finish this off, in case anyone has the same problem, there are two screws as in the picture below. I had to grind one of them out with a dremel but they are just M5 x 9.5 with an integral washer, so not hard to replicate. The aluminium plate holds the plastic cup in.
It still wouldn't budge with the screws out so I put the cap back on and gently tapped it with a hammer until it popped out of the alloy housing. I gave the whole thing a good clean up and made sure the inside of the channel which held the seal was completely free of any scale and muck. There was fair bit of crud in there to start with.
I got a 47 ID x 3mm CS EPDM O ring as that is what I measured it to be, but it was too big and wouldn't stay in the channel. So I bought a 46ID x 3mm CS and that fitted perfectly. The plastic cup is however a very tight fit, and easing it into place dry kept pushing the O ring out, so I used some red brake grease which didn't help much until I warmed the alloy housing with the O ring already fitted and then carefully pressed it back together. You can see through the plastic, just enough to see the O ring in place, to check it hasn't popped out.
Then back together with a new piston and seal, spending far too much time working out which that pesky spring fitted and working out a way of refitting that rubber cup onto the end of it. Big end goes in first with the smaller end and it's plate fitting inside the rubber cup. I ended up luckily finding a small metal tube with the same ID as the cylinder, and pushing the cup into it, then sliding the tube into the cylinder and pushing it from one to the other with a 3/8" socket extension,
I have sealed off the outlet, filled it with D4 to check it doesn't leak, and left it for week. No leaks so will chuck a bit of black paint on it shortly and refit.
Brakes all sorted
D'oh!Somewhere, over a rainbow, weigh a pie.
1976 KZ900
