SRX Master cylinder

[Mart]

Any one else have problems with the neoprene diaphragm seal under the lid of the SRX front brake master cylinder. The ones I have used seem to swell when in contact with the brake fluid.making them unusable. The latest one to suffer this is only a couple of months old. @ £6.15 a throw this seems an unecessary expense. Someone has suggested using silicone based fluid in which case I could just use a home made seal around the lip of the lid and dispense with the diaphragm as I assume this is only to keep moisture away from the dot3/4 fluid in current use. Any advice would be appreciated. Cheers Mart

[Steve H]

The seal is made like a bellows so that when the fluid drops the seal follows the fluid and avoids a vacuum in the reservour, (which would pull the brakes off)
I would stick with the recommended fluid as you risk knackering the other, more critical, seals.
Not the same but I've found that, if dried and left out overnight, CV carb diaphragms will go back to their normal size. Might be worth cleaning the m/cyl diaphragm and seeing what happens.

[Mart]

Thanks Steve, That's about what I thought. Also you have to strip the entire system and remove any trace of d0t3/4. Apparently any cross contamination causes problems. I think I will try and make sure the bellows are not in constant contact with the fluid by keeping the fluid levels low[ish]

[Steve H]

To my way of thinking, the seals are designed to work with a specific type of fluid, threfore I would stick to the recommended fluid.
I know you said the diaphragm was expanding, but why is this causing a problem ?. I can see it being a problem if you are taking the cover off all the time, but I would have expected this to be a once a year thing, when the pistons seize.

[Steve Lake]

I agree with SteveH (well, you have to don't you!) I would completely purge your system....'cos its possible contamination is causing the problem....then clean the seal thoroughly.....before refilling and bleeding....use NEW fluid...do it in the garage.....in as dry an atmosphere as possible.

my resevior is mounted on clipons....and i have to lean the bike over to get the master cylinder level, then when it's all bled (a tedious, long whinded process on these bikes) i top it up and close it all up, when the bike is upright over half the seal is immersed in fluid.....and i have never had a leak, or had a problem with the seal swelling or deteriorating