Leaky MC Cap

[Staffords]

I have the apparently common leak around the edges of the cap from my 68 Barracuda master cylinder. The master cylinder is for disk front and drum rear, with the 2 different size reservoirs for front/rear. It weeps around the cap/gasket surface, enough for to cause the OEM style cast master cylinder to have surface rust and a few drops have damaged the paint on my detailed engine bay

I keep the fluid level about 3/8" below the edge of the reservoir. The master cylinder sealing surface is flat by straight edge with no visible defects. The gasket appears to be intact.

I'd like to try replacing the cap/gasket before i go through the trouble and cost of replacing the entire master cylinder. Does anyone have a part# or link for the correct cap and gasket?

Any other suggestions for sealing this type of master cylinder other than just replacing it with one that uses a screw on cap for the reservoir? I hoped there might be some kind of gasket sealant that could be applied to the edge of the sealing surface, but I think brake fluid destroys everything.

 

[RedFish]

Unless you are a purest, there are alternative units that dont have the same flaws. I think from a Neon was a popular choice. Just a suggestion. Sure aftermarket could make a Gasket that doesn't leak but,,, they don't. Tightening and retightening a bolt in center would be about as effective as more bend in the bailing wire.

 

[Professor Fate]

Okay, which master cylinder do you have?
Stock '68 disc master

or the newer '73 and up disc master?

Factory original on left, current parts store replacement on right.

 

[Staffords]

Unless you are a purest, there are alternative units that dont have the same flaws. I think from a Neon was a popular choice. Just a suggestion

I know, DrDiff sells one. If a new cap/gasket doesn't solve the issue I will probably replace the master cylinder, but a new cap/gasket is much cheaper/easier.

 

[Staffords]

Okay, which master cylinder do you have?
Stock '68 disc master
View attachment 1716459705
or the newer '73 and up disc master?
View attachment 1716459706
Factory original on left, current parts store replacement on right.

Mine looks like the current parts store replacement on the right.

 

[Lift&Move]

You can bend the hold down clip to make it tighter, and try that

 

[Professor Fate]

Yeah, try bending the wire bail (front and rear) so it clamps a little tighter and see if that helps.

 

[Murray]

I would still want to file the gasket surface to flatten and smooth. Then a new and softer gasket. I run an NOS M/C with no leaks.

 

[Staffords]

I would still want to file the gasket surface to flatten and smooth. Then a new and softer gasket. I run an NOS M/C with no leaks.

Yessir I'm looking for the new, softer gasket. Anybody know the part number?

 

[Kendog 170]

If you have this style you could bend the hold down clip to give a little more tension. I remember doing it to a 74 Vaillant I had once.

 

[QWKSLVR]

I had the same issue with my m/cyl also. Clean top surface of master cylinder, inside of cap where gasket sits AND the gasket as well. Cleaning the gasket along with lowering the fluid level fixed my problem.