Master cylinder woes. I think I'm going mental! HELP!

Not for an SV I should point out hence in bike talk.

I managed to accidently pump out a piston the other day so I've decided to take the calipers off andsort them out.

Master cylinder was run dry. Today I put the calipers back on to pump out the remaining pistons. Put brakefluid in and nothing.

Lots moremessing around and Inow have the master cylinder in the sink. I can blow up the outlet with a bit of pressure and it comes out of the reservoir. When I blow and push the piston it blocks it, as I'd expect. However if I push the piston it won't push anything, not brake fluid, not water and not air (I think).

What the **** is going on?! It was fine a couple of days ago to push one of the pistons all the way out and the other three partially. I've tried lots and lots of brake cleaner and hot water but nothing's clearing it, if it is indeed gunked up.

Help me. Please.

[yorkie_chris]

Strip it down and have a gander, maybe the seal has flipped itself over?

[Sid Squid]

I had a phone call that described what the problem was .

[yorkie_chris]

Which was?

Squid that was the problem before the current problem (I was the problem that time!). It is still a problem though. It worked days ago and now it doesn't. Looks like I'll have to buy some circlip pliers.

EDIT:
I've now got circlip pliers and have taken the MC apart.

Here's my one followed by a pic of the rebuild kit.





Mine seems to be in good condition but are the seals in the right place and do they look the right way round? I'm a bit confused why the rebuid kit has a cup without a hole in it?

Found this pic on the net which has reassured me that my one is correct.



I've refitted it together and tried using vegetabl oil. When I pump away nothing at all happens! The seal is ok and the cup seems to be sealing ok too.

[yorkie_chris]

Can you see through the transfer port with it split apart?

I don't know what that is but I can see through throught the little window inside with tiny holes in it and I can see into the bore through that. There's one little hole. It's all very clean. The MC can't be split.

After literally no sleep (not because of this!) I have had divine inspiration. Maybe it was the tiny bit of mackerel I just ate. I filled up the reservoir with water and held the MC at 45 degrees. Then I just pumped and pumped slowly. Guess what? It does work. I think I've been doing it with so much haste I hadn't seen it. There is so little fluid moving out of it but it all clicks together. The force from the lever is reduced to a little hydraulic force, otherwise the lever would be so hard to pull it'd be silly and uncontrollable. Is this right or just the ramblings of an idiot? If I am right and it all works fine I have a few questions.

I've read, and done it on another bike, that to clear any air in the brake lines you can tie the lever in for a few hours. This worked on the other bike. However when I blow in the outlet with the piston pushed in it's completely blocked. Does this work by allowing the air to travel right up to MC and then when the lever is released pulling it out (or at least not pushing it down again)?

Can I blow in the outlet of the MC and get bubbles in the reservoir with the piston in it's resting position because if not the hydraulics would constantly be pressurised and the pistons wouldn't release the brake disc?

Am I an insomniac genius?

Finally what sort of internal bore are brake lines?

[Sid Squid]

Originally Posted by teriyakimonkey

Can I blow in the outlet of the MC and get bubbles in the reservoir with the piston in it's resting position because if not the hydraulics would constantly be pressurised and the pistons wouldn't release the brake disc?

Yes. When the piston is retracted, (in the rest position), the hole in the bore closest to the banjo is open, this allows fluid to return to the reservoir, (or hose thereto), such that the brake can retract.

Originally Posted by teriyakimonkey

Am I an insomniac genius?

Unquestionably. Without a shadow of a doubt.

Originally Posted by teriyakimonkey

Finally what sort of internal bore are brake lines?

varies a bit but small, ~2mm.

Don't pump the lever quickly, the brake fluid is a thin liquid but has a certain viscosity, the ports in the cylinder are small and the liquid doesn't flow through them quickly.