I've recently switched master cylinders three times on my '68 with power discs. Each time the MC has leaked from the top despite having new rubber inside the cap. Otherwise the actual stopping power of the system is excellent. Is there such a thing as too much brake pressure? There are no restrictions on down the line and most brake lines and all hoses are new, as are calipers and wheel cylinders.

Also, a couple of my line connections (at proportioning valve & with hoses) are a little damp from slight leaks. I have tightened the nuts as tight as possible without breaking something. Is there any tricks to sealing these junctions?

Always something!

 

I dont know what to tell you about your master cylinder, but for your connections, you could prbably use some teflon (pipe tape) but be careful not to get it over the hole as to keep it out of your lines. My master cylinder leaks also I and have just put on new rubber. Thats all I can tell yah. ~Mike

 

Teflon tape wont help a leaking flare fitting when you did those line did you do a double flare or a single flare it is suppose to be a double flare with 45 degrees of taper, Good luck to ya, if you let the cap leak will it leak till its empty ? I have seen quite a few that just leak a little "OFF THE TOP" and then their fine and there should be any great amount of pressure inside the resivior anyway the rubber just keeps it out of the elemnets

 

Sorry otto I wasnt thinking straight, I forgot all about the flare, i was just jumped straight to the threads. I think he means that alot leaks, mine does it when I get alot of bouncin, and its not just a little off the top, often times my cylinder gets pretty close to empty if I dont check it more than regularly and im totally positive its coming from the cap, not from any of my brake components because theyre brand new and have been looked at many time. Thanks,
Mike

 

 

Hey Otto, all of the lines are off the shelf from the auto parts store. They are double flared so I don't understand why they are not sealing properly...tis frustrating.

The MC erupted like a volcano while merely bleeding the brakes and pumping up the pressure. I could see a little leaking out on a rough trail or even in the urban jungle, but to have it blow out the top while just sitting is quite perplexing, especially considering this is the third MC. Thanks for the thoughts.

 

Buzzard, If your MC erupts when you are bleeding the brakes, it means something is being expanded to accept a lot of fluid, then when you let off the Pedal, the Expanded part contracts enough to force a lot of fluid back up in the MC.

It just means the Rear Shoes (most likely) are not adjusted as close as they could be. Lots of travel out there somewhere.

However if you have fluid forcing its way past the MC Cover gasket while your driving, it means you still have Air out there somewhere.
You are lucky the excess fluid is leaking out the Top. In the older trucks with the MC's Screw down tops, the Hot air would expand the Shoes and bring you to a Halt.