Leaking Brake Fluid!

I just rebuilt the master cylinder on a 75 Z1b. I put the whole brake system together and bled it. Works great except for one problem. The brake fluid is now leaking through the cap! It has stripped the paint of my triple clamp and now the bike is grounded till I can fix the problem. Is the rubber diaphragm the seal for the cap or is it something else? If it is the rubber diaphragm, where can I get a new one? Would I be able to use one from a auto parts store for a car master cylinder or not?

I would think your local Kawasaki dealer could order one if not in stock. I recently rebuilt my master cylinder. My rubber diapgram seems in good shape and is not leaking at this point. My 77 KZ650 B1 has the round screw top fluid reservoir. There is one more part in there besides the rubber diaphram. It is a white delrin type ring. I believe it acts a a washer and bearing surface so the rubber diaphpram does not get chewed up when tightening down the cap. Post up what you find out.

The diaphram and plate are still available through any dealer. $18 for the diaphram, $5 for the plate at bikebandit.com. If it's leaking, these will fix it unless the master cylinder is broken. There's been some confusion in the past as to how the diaphram works. Some guys think the brake fluid is even vented to the air. Wrong. If you look at the master cylinder cap you'll see a slot to let air in, but air only goes to the center of the diaphram. The diaphram is like a spring and extends and contracts along with the brake fluid level to take up space in the master cylinder as fluid level drops. Air never gets to the fluid and fluid can't leak to the air unless the diaphram is broken.

z1 enterprises

I have not been able to find the diaphragm at z1 enterprises.

About $19 for both parts at babbittsonline.com.
www.babbittsonline.com/pages/parts/viewbybrand/default.aspx

I went to my dealer and ordered the diaphragm and the plate. Thanks for the help. I hope this fixes the problem.