ebay ypvs front brake master cylinder window leaks

[JonW]

As has been said a few times on here in other threads, there has been leakage with the ebay master cylinder windows.

To be honest I didnt think any of mine had leaked, until I pulled out my F1 to work on the other day and saw this:



I'm not 100% sure where the leak originates, when you look at how these fit I thought the 'glass' (mineral of some sort?) sat against the O ring which then made a seal. That would mean that the steel ring around the glass and the edges of hole in the master cylinder itself were not expected to seal.

My seal is quite compressed and I would think doing its job. This means that either:

1, the o ring as supplied is not brake fluid safe and breaking down
2, the o ring isnt the issue here and the fluid is escaping through:
2a, the glass itself
2b, there is an part of the hole the window sits in that is allowing fluid through to where the outside of the steel ring sits

Has anyone found a more trusted o ring and fitted it?

Has anyone found there is a point where the fluid can find its way out that isnt covered by the O ring?

[stirling11]

UPDATED

Just read your post on Legends lines, so you know about the DOT3 issue, so updated to check on the type of rubber used in the o-ring, I'd hazard a guess that will be your issue, I'll keep the info below for other peoples benefit

The first question I'd ask is what DOT rating of brake fluid are you using, DOT3 is generally the one that's recommended on the cover of the master cylinder in bikes (and cars) of this vintage

If you are using anything other than DOT3 then you may have a compatibility issue with the type of O-ring used, you've probably already guessed that

The original Japanese chemical regulations from many years ago (circa 1990's) banned anything other than DOT3 due to an ingredient in the make up that was illegal in Japan, most people that weren't in Japan, mechanics included, just used to top up or replace old brake fluid with DOT4 as that was the new standard, when DOT4 was used the rubber brake lines were not compatible with DOT4 and when pressure was put on the brake pedal the rubber parts of the lines would swell out because the rubber was denatured by the DOT4 and the brakes wouldn't work, I actually saw the issue on a 75 series ute that couldn't get the brake pedal to harden up

That's not to say you won't have the same issue with DOT3 depending on the type of rubber supplied with the glass and the material of your brake lines, if you've gone to genuine Yamaha then you may have the same issue with anything other than DOT3 unless Yamaha has changed the composition of the rubber in the lines

Have a look at this link and scroll down to Brake Fluid DOT3, it will show which O-ring materials are suited to DOT3 and other fluids

www.marcorubber.com/o-ring-chemical-compatibility-chart.htm#chemId=304

Newer vehicles don't seem to have this issue


HTH