Front Master Cylinder Rebuild on Rear?

Thank you stonehill

Honestly, the ONLY reason I could fathom anyone wanting to even consider it would be to get a straight shot at the relief holes to clean them if they were really gummed up. But even then you'd have to deal with re-sealing the opening, because I'm fairly certain there's no way of getting the original plastic plug out without destroying it.

That's exactly my thoughts. I don't have any extensive experience with them, have rebuilt just three of these rear master cylinders, and so far there was no need to take a look at these holes and removing the plug. I almost did with the first one but it looked like this plastic plug would most likely get destroyed in the process so I gave up, and very glad I did. I see now how it is kept in there - there is no way to smoothly depress those clips. Those plugs are not listed in the parts list, but perhaps they are more universal than we might think, as they were manufactured separate from the body itself. Maybe they fit others as well and are available from master cylinder manufacturers? A long shot for sure. Having a lathe would make making one easy, but even on a bench one could be made from brass, and pressed in tightly with some jb-weld or red locktite to ensure staying in place.

Next time around I'd also do what kawboy suggested - switching to D0T 5 fluid. I had D0T 5.1 which I'm using on all other bikes, so for simplicity I just decided to stay with it. From the perspective now, since all the brake system components were completely rebuilt on my bike so everything was spanking clean and dry, I wish I had filled it up with D0T 5. I was really careful and luckily non of the black paint came off when bleeding the calipers.

stonehill wrote: Yes it is removable.

Hm. Good to know.

(You don't happen to have any extras lying around, by any chance? )

stonehill wrote: Yes it is removable.

Well, now we know. the second pic shows the plug less the o-ring I suspect. I see the groove and the only way that plug would seal is if it had an o-ring.

Like I suggested: A thin, well fitting disc of thin plastic (simply a backing) and fill with epoxy (JB Weld- metal filled)

My 1980 KZ1300 started leaking from the rear master cylinder recently, I took it all apart and as it was probably original it was very rusty and mucky. I cleaned it all up and re assembled it but as soon as I applied px it leaked, badly. Apart it came a second time, both rubber seals are in decent shape so I put a ring of .025 aviation stainless lock wire under both to lift them up and apply more px on the seal. I must admit I wasn't sure it would work but now several weeks on and multiple brake applications there are no leaks. This bike is a keeper so I will buy new rubbers but just thought I'd pass this on in case you need to do a temporary fix to get you home or whatever.

No comments on this? As the seals move on the shaft a bit and if you raise them a bit they will have more pressure on the sealing surface, I was going to use .032 lock wire but had none at home so .025 was used , so far so good.