Master Cylinder Leak

[dfrazz]

My '71 Chally came with power drums and I converted to power discs on all 4 wheels. I bought a basic master cylinder from NAPA that has a small reservoir in the front and large in the back.  It is leaking in the front corner engine side.  I have replaced the gasket and master cylinder itself but it still leaks.  Do I need a HP cylinder or one with equal reservoirs?

[dutch]

many of them repro MC`s leak from under the cap.  Try putting some more tension on the clip that holds it.  Some use a double gasket,  I put a couple pieces of platic tube around the clip where it pushes on the cap. It seems to be leak free now.

[burdar]

That's a good idea Dutch.  I actually put a very thin layer of RTV on the sealing surface.  It hasn't leaked at all since.  The problem is that the top of the master cylinder isn't a machined surface.  The cap is supposed to seal on a "as cast" surface. 

You could always upgrade to a new aluminum master.  They have screw on caps that won't leak.  Those masters have a two bolt flange.  You have to use an adapter bracket to use them.

[dfrazz]

That's a good idea Dutch.  I actually put a very thin layer of RTV on the sealing surface.  It hasn't leaked at all since.  The problem is that the top of the master cylinder isn't a machined surface.  The cap is supposed to seal on a "as cast" surface. 

You could always upgrade to a new aluminum master.  They have screw on caps that won't leak.  Those masters have a two bolt flange.  You have to use an adapter bracket to use them.

Thanks guys.  I've always been nervous about putting RTV inside the MC, but I guess if it is between the gasket and lid it should be ok.  I checked out some upgraded MC's (Strange Eng) and it takes a $40 adapter plate like you said.   

[Bullitt-]

Just thinking out loud.. take the seal out of the lid n see if the lid sits square on the MC... if not a little twist of the top might make em match up better. 

[burdar]

Just to be clear, I only put a very thin amount on. It basically only filled the low spots in the cast finish of the master. It wasn't thick enough to get pushed out the sides.

[dfrazz]

Just thinking out loud.. take the seal out of the lid n see if the lid sits square on the MC... if not a little twist of the top might make em match up better. 

Good idea, thanks.  Its too coincidental that both MC's leaked in the same spot.  I also am running a vacuum pump but that should not have anything to do with the MC leaking, right?