Strange leak on brake master cylinder

[William2]

Interesting one this! I have a new brake master cylinder on my car and it appears to have a small leak underneath the main reservoir. Every couple of days, if you put your hand underneath there are signs of brake fluid. There is no sign of any leakage from the brake pipe union nor from the piston/cylinder. This is whilst the car is stationary in the garage. It's as if the aluminium housing is porous or has a small hole in it's casting. Has anyone else had a problem like this? As an aside, I would like to fit a nylon cap rather than the ally cap that is standard as it does not twist on very well. Does anyone know if these are available and who stocks them?

[richardcox_lotus]

Yes I get similar, but I'm not convinced it's brake fluid. I think it may be some form of condensation, else a tiny tiny leak as my levels don't seem to dip

[nmauduit]

I had a similar leak on my tandem MC (federal) S4 : not from the pressure circuit since it did not change when applying pressure even overnight. Not a big leak, but I did not like the moist feeling in that area... It was the gasket between the top tank and the MC (the tank is a bit exposed and makes a strong lever on the junction ... and it happened that a "pro" mechanics had looked into it, a bit too brutally for elan is my guess, and had shaken the MC by the tank). After the gasket was changed the MC became dry... just a thought.

[david.g.chapman]

I get the same thing on my brake MC and clutch MC - simple types with no plastic reservoir and aluminium screwtops.

I minimise it by not filling the cylinder to less than 10mm from the top - it is probably fluid creeping past the rubber washer under the screwtop - which never seems to seal completely...

Dave Chapman

[Europatc]

Hello, I would agree with David, I suffered the same fluid loss, it was just seeping past the rubber washer. I bought one of those spanners for the master cylinder cap, gave it bit more of a nip and its now dry
all the best
Stuart