Master Brake Cylinder seeping

1979 kz650, and I'm in the middle of nowhere, halfway across the Pacific, so no parts. My master brake cylinder in the front is seeping . . . not leaking really, but seeping or oozing brake fluid from the lower gasket. I wipe it dry in the morning, and by evening, it is wet all over again. There is not enough loss to cause drips, or to lose too much fluid, but the slow leak is certainly annoying and destroying the paint on my handlebars on that side.

So, the reason for the question: Is there a way I can fix this without new parts? I don't have access to used or new parts, and getting any sent will take months. Is it possible to put some sort of sealer around the perimeter of the gasket? The brake function is normal and I probably will have to fill the reservoir in another few weeks or something. I am really just looking to have this functional before I go buy a new master cylinder.

not sure where it is leaking? is it at the banjo bolt? is this the round(B1) or rectangular(B2,3) shaped master?
what part # in the pic is leaking?

B1



_____________________________

B2,3

b4schroer wrote: 1979 kz650...in the middle of nowhere...no parts. My master brake cylinder in the front is seeping...Is there a way I can fix this without new parts? I don't have access to used or new parts, and getting any sent will take months. Is it possible to put some sort of sealer around the perimeter of the gasket? The brake function is normal and I probably will have to fill the reservoir in another few weeks or something. I am really just looking to have this functional before I go buy a new master cylinder.

For reference ---
redlinecycle.com/Brk%20-%20Trap%20Rsrvr%20O-%20Ring.html

The o'ring gets old and hard and flattens out, which then starts leaking.

I used an o'ring from Redline with good success.

Have never tried using any type of sealant with an old o'ring in this application. But there might be some sort of sealant available that's resistant to brake fluid. Perhaps one of the Permatex products.

Another option may be converting to Dot5 silicone based fluid (the purple stuff) , which won't harm paint.
Never "mix" Dot5 with other type brake fluids.

Good Fortune!

It is leaking from the part with no number on the diagram. As I suspect, this part . . . the main body . . . probably doesn't come apart. At the bottom of the cup if you will, there is a gasket, or at least the appearance of such, that runs the perimeter of the reservoir. It is in between the plastic cup and the metal mounting part. It just sort of oozes out of there with no apparent, exact place of leakage. I don't think it is o-ring related since it isn't leaking from anywhere the o-rings are at. It is also NOT the banjo bolt. I hadn't thought about a different brake fluid, that is a great idea . . . although the thing stays moist enough to make me still want to fix it.

Thanks for the replies . . . I'd still like to hear from someone that knows it can be sealed off(or not). Otherwise, in a couple days, perhaps I'll be the first and can report outcomes. I also want to avoid paying 75?? bucks for a used one in salvageable shape. That seems excessive.

Should be able to see two small holes through the floor of the reservoir. These are the supply port and the relief port.

When looking at the two ports, may also see the heads of two screws that hold the reservoir onto the main body of the master cylinder.
Sometimes there is a plastic gismo on the floor of the reservoir that fits snugly, but may be removed in order to see the actual bottom of the reservoir with the ports and screws.

What is seen when looking inside the reservoir at the bottom of the reservoir?

Good Fortune!

.

Thanks, martin_csr!




In the following rear master cylinder diagram from 1976 KZ900-B1 LTD FSM, part #12 is located on the reservoir floor.





Note that the reservoir is cast as a permanent non-removable component of the master cylinder.

Am uncertain but guessing that the leaking master cylinder in question is either a round barrel style or the trapezoid style.

And also guessing about whether the reservoir is removable, and whether something like part #12 might be blocking visibility or access to some screws that perhaps attach a removable reservoir to the master cylinder.

Might be wrong, but doubt that a non-accessible gasket would be included in the design and manufacture of the master cylinder, between the reservoir portion and main body.

Good Fortune!

No eBay APP ID and/or Cert ID defined in Kunena configurationNo eBay APP ID and/or Cert ID defined in Kunena configurationSame issue on my '78. Have you taken the cover off recently? My guess is that the diaphragm is torn. You'll need a new diaphragm, but the problem is that they are not available (even though many sites show them as active). You may be able to seal it up with something, but without the diaphragm there I'm not sure how it will work. Your next option is to save up for a new MC. A lot of people have gotten these and liked them:

Here is a full MC with the diaphragm (assuming you have the trapezoidal MC?): For that much $$$ though I would just buy a new MC rather than another 30 y/o replacement that may tear in a year...

In the meantime you can put something absorbent around the MC to stop it from ruining your paint too bad... (Sweatband, bandana?)

b4schroer wrote: 1979 kz650....

Standard, custom, or SR?
Round or trapezoid master cylinder reservoir?
Single or dual disc front brake?
14mm or 5/8" m/c bore?

Good Fortune!

Patton wrote:

b4schroer wrote: 1979 kz650....

Standard, custom, or SR?
Round or trapezoid master cylinder reservoir?
Single or dual disc front brake?
14mm or 5/8" m/c bore?

Good Fortune!

No idea . . .
Trapezoid
Dual discs
No idea.

I found the two screws on the inside of the reservoir a long time ago, and attempts to remove them only yielded them starting to strip. They refuse to budge. The MC is not leaking from the diaphragm. On the trapezoidal MC, there is a clearly marked border where plastic meets metal. While it makes no sense that a gasket here wouldn't have a replacement . . . it is definitely seeping from that location, and it looks very much like a gasket from what little of it I can see. In particular, the reservoir is definitely NOT cast, as someone previously wrote. Certainly part of it is, but there is a whole lot of plastic going on there too. Side note: the interior of mine looked just about exactly like the picture shown . . . nice and dirty and nasty. The leak prompted me to do what should have been regular maintenance which I had been avoiding for about a decade now.

The only paint it trashed is all the paint on the cast part of the MC. It hasn't damaged the chrome handlebars and doesn't drip onto anything below. It's more of an annoyance than anything else. I may just use some cash for a NEW mc . . . I definitely agree to avoid buying a 30 year old part that will break next year.

I appreciate all the replies. At this point, my game plan is to buy some sort of sealing agent, and after drying the outside of the reservoir thoroughly, I will apply a nice bead around the entire perimeter where the plastic meets the metal, and I'm guessing that as long as the agent is resistant to brake fluid, I'll be ok. Any thoughts on good agents in addition to the mentioned one early in the thread? I'll go shopping tomorrow.

Patton wrote: ...For reference ---
redlinecycle.com/Brk%20-%20Trap%20Rsrvr%20O-%20Ring.html
The o'ring gets old and hard and flattens out, which then starts leaking.
I used an o'ring from Redline with good success....

Mine was doing the same thing.
Am reasonably certain it's the o'ring.

Good Fortune!