Front master cylinder 82 GS650G Model Z tricks?

[Michael]

Due to my schedule I am only now managing to remove the piston. Turns out the application of heat and gentle use of a mallet was key, obviously the inner sleeve had corroded to the cylinder locking the piston in place.

Thanks for all the suggestions! I can't wait to take it out tomorrow, after I bleed the lines of course.

[Gorminrider]

well, I'd be thinking you need a new master cylinder, really. otherwise you can try to hone the cylinder, given your description, but seeing as you aren't going into mechanics too deeply without a shop for a bunch of eclectic tools, a new one is best.
But, out there in the parking lot, I can imagine myself with a collection of wet+dry sandpapers and a dowel-to-fit too.. just be aware the piston cups need to fit tight and round. you don't want to take too much off the surface to get rid of pits or you'll be living life on the riskier side when you give those brakes a hard squeeze down the road...

[Michael]

I can imagine myself with a collection of wet+dry sandpapers and a dowel-to-fit too.. just be aware the piston cups need to fit tight and round.

That's exactly what I did once the piston was free, 400 grit to remove the "varnish" from the old fluid. The piston rides nice and smooth now!

[Gorminrider]

..... and it's just an aside but I remember in the olden-times something about oversized piston cups when I honed a car's wheel cylinder. Modern method is just to get a new assembly for all the work,danger and nuisance that too much fiddling will make clear- so if yours turns out to be beyond hope....

but it sounds like you "are getting away with it" ride on! (but gently at first)