Brake Help please

[Demon1775]

Ok I have an 82 cb 750f when I got the bike the rear master cylinder was leaking so I bought the rebuild kit for it. For about a week it worked just fine then it started leaking again at the bottom around the boot. So I took it apart cleaned it really good checked all the seals they looked fine but still leaked. So I got another kit thinking maybe the one I got was faulty. Same story worked good for a few days but now when I press the brake its leaking like it has no seals in. My only guess is that the housing has something wrong with it and that seems to be next to impossible to find one. Any ideas on other things to check or where to find a diff housing. Thanks  

[Re-run]

Are you talking about the fluid reservoir or the master cylinder?
With the cup, I could see 2 things.
1: either the bottom of the cup has a crack, or the hose is bad in a spot.
2: There is a lid, plastic ring, and diaphragm. I had the plastic ring crack on my master cup and it would leak around the lid.

If it is the master itself, I could see 2 things there but both kinda tie together.

1: The parts were not dipped in brake fluid as they were assembled.
2: Without knowing what your rebuild kit contained, the oring for sealing might be the wrong shape or slightly small, or the piston has rough edges that may be ripping the oring.

The only other spot I can see being an issue is the nipple that the short brake line connects to on the master. It may not be sealing where it connects to the master.

Best I could think of from looking at the manual.

[Demon1775]

Thanks re-run and yes the master is whats leaking its coimg out down where the dust seal/boot that the rod comes out of to connect to the brake. When i apply the brake it leaks and once i let off the brake it leaks. Its like its gravity bleeding the rbuild kit is OEM reference number 43520-461-771 that a local shop got in for me. Yes i lubed it with fluid both kits and did not notice any ripping in any of the seals. I ve not seen any cracks anywhere in the housing. Ive read over my manual and im stumped Ive looked to find another housing and thats about a lost cause. Im gonna pull it apart again tomorrow clean and inspect it all once more and try again.

[Re-run]

Pay special attention to the piston that moves inside the seal. It may be that it has sharp edges that are cutting the seal after everything is assembled.

[Demon1775]

Will do I tnik i found part of the problem the grove that th snap ring fits in had some crud in it when i pulled it apart today the ring and the washer were side ways a bit. Then the seal that sits on top of the spring now has a rip in it not sure how that happened. It looks like the spring pushed up threw it on one side.

[LukeM]

As an old Navy electronics technician told me some 35 years ago:

"There's nothing in the the world like a good visual inspection."

Luke M

[Demon1775]

Well after many times pulling cleaning and trying this that and the other I found the problem! The grove the snap ring fits in worn out temp fix used my dremel and cut the grove back out some.. Best news I found that a 82-83 cb900 and a few other bikes have the same master cylinder as mine so order one on ebay for 30 bucks that came off a 900. Now need I need to cross ref the parts number on the fork tube to find a new one of those.,