Master cylinder cap leaking

[charles messler]

hi guys,
My 71 furys master cylinder cap I see leaking to the point where there is almost no fluid in the front compartment. I replaced the master cylinder about three years ago after one I put on failed after a couple of months in use. I've tried bending the bailing wire and filing the edge of the master cylinder which stops it for a while. Then it starts up again out of the blue.

 

[Yatzee]

hi guys,
My 71 furys master cylinder cap I see leaking to the point where there is almost no fluid in the front compartment. I replaced the master cylinder about three years ago after one I put on failed after a couple of months in use. I've tried bending the bailing wire and filing the edge of the master cylinder which stops it for a while. Then it starts up again out of the blue.

This is a rather rare situation unless you are over filling the unit. Fluid generally goes down as the pads and shoes wear and the rubber bellows on the underside of the cap is pulled down due to an internal vacuum in the bowls. A poorly functioning ball check in the bottom of the master will shoot fluid upwards as the master piston returns or if an internal seal is damaged but you said you replaced the master with the same result. If it does squirt up, excess fluid on the rubber seal can seep out. I suspect there is pressure being created inside the bowls or the cap seal is of poor quality. Try lowering the fill volume and see what happens.

 

[70NEWYORKER]

I had the same issue. Master was always sweating fluid out after a drive. The leaking master was a replacement I put on in the mid 90's. Original never did this. I chalked it up to the Hipo manifolds cooking it after several hours on the freeway. Tried different lids and tightening up the hold down..no luck. I had the hold down so tight I needed a tire iron to move it! That master started leaking internally a few years ago so it got replaced. No more leaking/sweating fluid!! I figure the casting was porous and would "open" up when hot.

 

[Pete Kaczmarski]

I would also check the casting of the master cylinder near the cap area to see if it is even and flat.

 

[71Newp]

I had the same problem. I finally bought a new master. Before going through the hassle of replacing the whole thing I tried the hold down from the new one on the old one and it fixed the problem!