MC Reservoir leak: home-made gasket?

The Master cylinder on my wife's CX500 leaks occasionally. I replaced the
o-ring on the reservoir, with no real effect. The leak appears to be from
the top of the reservoir/cover area. When the bars are turned at various
angles, the reservoir is no longer level, of course, and the brake fluid
reaches the top of the reservoir.

There is no diaphragm or gasket there to ensure a tight fit on those
surfaces. Any reason I couldn't cut a gasket from a piece of bicycle inner
tube?

 

I suspect there should be a diaphragm. All of my Hondas (including an
'83 CX650 Turbo) have had them. Check the parts diagram at your dealer.

Before resorting to bicycle tube material, soak a sample in brake fluid
for a couple of weeks to make sure it's compatible.

 

I don't think it will stand up to brake fluid. Brake fluid is nasty stuff
and you will need some type polymer that is made to resist deterioration.

Dave

 

If there's any place on the whole bike that doesn't seem like a good
place for experiments, I think this is it.

On my bike, (not a CX500), there's a rubber bellows thingie
that sits at the top of the cylinder. Why not beg your dealer
for a peek at the parts fiche and then replace the suspect parts
with stock new ones.

 

DEFINITELY!

Not being able to go cannot kill you.

Not being able to stop CAN!

And inner tube rubber will NOT stand up to brake fluid. On any type of
fluid reservoir there will always be at least an O ring or gasket.
Someone probably removed it. A new oil ring or diaphragm will probably
cost $10-15 but even if it's $20-25 it is worth it not to mess with
the brakes.

Fred

 

OK, thanks for all the helpful comments. I kind of knew the answer before I
asked. Appreciate the re-inforcement, though.
Brent