I recently had a low brake pedal and when I went to check the reservoir hydraulic fluid was low so I filled it and noticed that there was some oxidized brake fluid in the to of the reservoir. I cleaned it up and noticed a crack in the cap. I ordered a new cap and gasket and thought that was that. But... the new cap and gasket seem to be allowing brake fluid to still back up (slowly) onto the top of the reservoir. Seems like there is some kind of back pressure. I have a 19mm master cylinder. I've looked everywhere and not leaks, peddle board off ete. etc. Any ideas???

Thanks, Tom

You are prolly using standard 17mm brake fluid with the 19mm MC. Try the special blue high performance 19mm fluid and it won't argue with you by trying to escape all the time.

I was experiencing the same issue. I put one of these in the cap and it solved the problem

http://www.928motorsports.com/parts/master...der_bellows.php

Thanks, I'll give the bellows a try.

You've lost me. My knowledge of brake fluid is numerical ie: #3,#4,#5. With #5 you don't have to worry about the paint but I'm using #4 and have never had this problem before. I'll try the bellows before bleeding my brakes.

Really ?, new to me.
A 17mm master requires different brake fluid ?
Do you mean synthetic vs. conventional ?
What is used in each and where can I find an explanation ?

My first reaction is quite different.
I thought the issue was likely a mal- adjusted (too long) pedal push rod,
not allowing needed fluid to enter the MC.

I'd like to see your source for that (mis)information.

The blue, in ATE Super blue, is just a dye. It has a boiling point in the same range as many many other types and brands of DOT4 brake fluid. The blue is only to help when doing brake fluid flushes, so you know when all the clear style is through the system. Or, when changing the next time, know when all the blue is through the system.

To the original poster, when is the last time you've flushed your brake fluid? I'd also hypothesize that it's maladjustment of the brake pedal.

It should be common knowledge but in the event that some reader didn't know, brake fluid absorbs water. The added water in the fluid changes many parameters about the fluid. This is why brake fluid should be changed on a time interval regardless of how many miles driven with the fluid.

I love it. And they explain WHY you need it.

Looks like something I could snatch off of just about any junk yard car on my next trip. I bet lots of res tops are the same size. seem logical.

Dude, I'm pretty sure he was joking.

Had you guys going there for a minute huh...

I was biting my lip Jeff, cause I knew you know better.

19mm fluid was so good, the 17mm Fluid Lobby got involved and got the DOT to actually ban it. True story.

There's still some 19mm fluid out there, but it goes for big bucks out on the black market. Every time it shows up on eBay they pull the listings...

Whew, you just restored my estimation of your sanity......best laugh I've had all day!

I thought it would be fun to lighten things up around here, hope you all had a good laugh. There may be more shenanigans in the future...jump in and help me out here if you are so inclined...

You can use 23/32 standard brake fluid in a 19mm MC in a pinch.

Seriously though - if your BF reservoir is blowing fluid out, you might be cooking your brakes.
Do you have a 'long' or soft pedal after driving for a while?

If so get out after a long drive and feel all 4 wheels.
If one is hotter than the rest, the caliper might be stuck/sticking and overheating.
This boils the water out of the BF and pushes it back up the system creating a air (steam) pocket.
If you really overheat them, the BF will begin to boil as well.

I believe that it is a Federal offense to use blue colored brake fluid. (The reason Super Blue is no longer sold).

Here is my GUESS. You may be over-filling your reservoir and when the brake pads retract pushing fluid back into the reservoir, some will emerge from the vent.

Correct you are: "It seems that the federal government has taken 15 years to figure out that Super Blue fluid is, in fact, blue in color."

"Apparently the Super Blue fluid has run afoul of the Federal Motor Vehicle Safety Standard after nearly 15 years on the market for being blue."

Thanks for the info.

I was told that you can get a dye to make it blue at home. No - really. Reminds me of my parents story about margarine, which could not be sold yellow. Also true. Or the story about the white salmon label in which the cheaper white salmon was "guaranteed not to turn pink in the can". Withdrawn after lawsuit.

BTW, I get more of what I would call a seepage at the top of the reservoir.