I just replaced the front brakes on my 06 F4i and also flushed the fluid. Now it leaks fluid (slow 1/4 inch line of fluid) from the master cylinder on the outside end of the cap that has the two screws to hold it in. I have checked for anything that would cause it to leak (dirt, stuff, etc) but nothing there.

A question though, when I removed the rubber diaphragm, it was pulled out like a accordion. When I went to put it back in, it fold into it's self. Do I need to pull it back out before putting it back in and do these need to be replaced once in awhile because they get old and leak? It seems it doubles as a gasket and could get ruined.

Also it seems like if the diaphragm is expanded, it will reduce the amount of brake fluid it will take to fill it. How much should it take, how far up the side should it be?

Thanks for the help! Read all the time, post very little but this is one I could not figure out.

Matt

 

I have an extra cap that I'm not using with the plastic and rubber insert inside, it's off an 2002 f4i so I'm unsure if it will work on an 06 but if you're interested you can have it if you just pay shipping.

 

Thanks Bow for the offer but I won't need it. I took it off again, cleaned it, and put it back together. It seems to be fine now. I also read that the diaphragm should be flat so I put it back that way. Looks like I solved it!

 

It's supposed to expand to minimize the amount of air ullage over the reservoir. That's normal.

You should fill the master so that the fluid is about half way up the sight glass on the side. There's no advantage to having more and the disadvantage of not being able to see the fluid line when you look.

As for the leak, could be the diaphragm is damaged.

 

Thanks for the explanation Berto. I think it's good now.

 

Not a problem matt, glad you figured things out.