Ok all you knowledgeable people out there, this is the story.  Riding along minding my own business  [moto] apply rear brake in traffic and pedal is all soft like nothing is happening.  Assumption correct, there is nothing happening.  Stop, get off, look for leaks, find none, ride home, start pulling stuff to bits. 
Brake pads are worn to limits so purchase new ones and install (might as well start with the easy stuff) but still no pedal.  I think this might be the case but hope it isn't.  Attempt to bleed brakes but no fluid comes through when pushing pedal.  Remove master cylinder.
Remove piston from master cylinder with some difficulty.  It's getting stuck in the white plastic (nylon, teflon, whatever) sleeve.  More questions...
Should the piston move freely in the sleeve?  It's almost like the spring can't push the piston back far enough.
Can I change the sleeve easily?
There is some corrosion evident around the circlip.  Is it possible that corrosion has put the sleeve out of shape and caused the piston to get stuck?
Thanks in anticipation of your advice.

Cheers,
Rob

Sorry, can't help Rob.  Maybe a call to Brad?

Quote from: heatherp on November 24, 2010, 04:55:18 PM
Sorry, can't help Rob.  Maybe a call to Brad?

Yup, I'm thinkin' so.

you can't buy spares for the master cylinder, you buy a replacement, they're not expensive, and depending on the mounting of your rear caliper, if the nipple is facing down unbolt it and turn it over, wedge something between the pads roughly the thickness of the rotor, bleed and reattach. turning the caliper so the bleed nipple faces up makes bleeding much easier.

paul.

Thanks loony888.  I'll duck down and get one soon.  Fortunately for me the caliper is on the top and I have a bit of hose that sticks on the end so it will be easy and mess free.