Clutch master cylinder piston

[frearther]

Actually, because I still couldn't get a perfect seal at the reservoir, the effective pressure on the cylinder wasn't 140 at all - and I worked my way up to that point. The piston popped out and traveled only about four inches - away from anything - or anyone - vulnerable. Not as daft as one might think.

Art

[M100]

Not as daft as one might think.

Judgement reserved

[simonriley11]

I've had this problem on several occasion in the past both with brake and clutch master cylinders. What has always worked for me, although I would mention that the piston has always moved a little bit i.e. never been siezed, is to hold the master cylinder in a vice and liberally squirt WD40 into the bore. Then push the blade of a large screwdriver into the end of the piston and push the piston in and out with the screwdriver, the piston should return as it has a spring behind it. The piston will gradually move towards the end of the bore (you might want to add some more WD40 as required) and eventually pop out. You have to be careful not to let the screwdriver come out of the end of the piston as you go and potentially score the bore. Assuming the bore isn't scored then it's just a matter of thoroughly cleaning everything and fitting a new seal kit.