Topic: cb550 leaky master cylinder

[paulages]

i'm leaking out of the circlip end of the piston. there was a small score in the wall of the cylinder when i inspected it upon disassembly, but it seemed that it would be beyond the position of the secondary cup and therefore irrelevant. was that a mistake, or was there likely something stupid i did upon reassembly? though it was very hard to do, i put the secondary cup exactly where it was on the old piston (and on ever other one i've disassembled), butted up against the inner lip on the piston. it is a slow leak, but is allowing air into the system.

[Chris Liston]

Best thing you can do is just get a modern remote resevoir master.  All the work you just did you deserve good brakes.  The stock unit is not that good.

[TwoTired]

Brake fluid crystalizes with age and coats the cylinder bore.  I rebuilt one with new rubber bits that leaked, and found a smooth crystalized coating in the cylinder bore.  Nice shiny and smooth.

I used a wooden dowel with a slot in the end. Put alum oxide paper in the slot (320)  and wrapped enough for a friction fit.  Chucked the tool in a variable speed drill and spun it in the bore 'till the glaze was gone, giving it a cross hatch pattern.  Reassembled with the exact same parts as before, and it hasn't leaked since.

A bore light from the gun shop is quite handy for master cylinder bore inspection, I might add.

Just a question.  Are you sure you put the center piston cup in the right direction? The cup edge should face the out bound hydraulic hole.  just checking...

cheers,

[paulages]

no, i'm not absolutely sure i put the center piston cup in the correct position, but i know that i put it exactly how and where it was on the old piston. it seemed correct. this would have to be the leak point though, wouldn't you think?

[TwoTired]

Yes.  That's the last line of containment.  You're going to have to take it apart again to see if you nicked it during installation. Check the inner and outer sealing edges for irregularity.

Or, it's a scratched bore... maybe.  The dust boot is not a seal.

Cheers,

[paulages]

yeah, i realize the dust boot is not a seal. i tend to understand things, but think that i don't, hence my asking for assurance that the center piston cup would be my problem.