New to me '72 FLH. When I apply the front brake, fluid comes out of the vent hole on the top of the master cylinder. My parts book shows part number 45012-72 for the gasket. This shows a gasket that covers the whole top of the mc. Another diagram shows a gasket that just goes around the perimeter of the top of the mc which is on the bike now. Does anyone know which is correct? It would seem to me that the one that covers the whole mc should be the correct one as it has a part number ending in 72. However, I don't want to cover up the vent hole if it is necessary for operation.
Thanks in advance.

 

The one you want has a paper rim with what looks like a latex center, it allows the MC to breath without fluild getting out.

 

Thanks Twisted. Obviously, the latex center has deteriorated and is no longer there. Would it be detrimental to run a solid gasket?

 

you missed the breath part of twists answer

 

I got that John. I guess a better way of putting it is what happens if it is a solid gasket and why does the parts book show one?

 

At the risk of being a PITA, is that part number good and that the parts book just isn't detailed enough or are there actually two different gaskets? Thanks again.

 

The 45012-72 is the one I put on my grandfather's bike. If fits fine of course. I haven't ridden it since then because I had the carb off waiting on a rebuild kit. It functioned fine rolling it around the garage. Sorry I can't be more help....

 

I found a picture of the gasket on Bob Luland's site and ordered 2 this morning. Parts book illustration just doesn't detail the gasket very well. It appears to be a solid gasket.
Thanks for the replies.

 

if the incorrect one is used the master if its not leaking out the top as its sealed, and it would develop a vacuum internally making the lever hit the bars at some point - the fluid would be pulled away from the master and not flow to apply the brakes -- as the brake pads wear down the space would become available to do that -- seen it happen

 

Thanks John for the explanation. New gaskets on their way. Still working through issues on newest acquisition. Never had hydraulic brakes on the front before. Thanks for the help.