Weeping Master Cylinder Plug

[JonR]

The previous post about the weeping MC cover prompted me to ask about my weeping MC plug. I have a 1966 Coronet Slant Six with the original one pot MC and 10" drum brakes all around. Now that I have rebuilt all 4 drum brakes and replaced all 4 wheel cylinders I still notice a very slow drop in the level of my master cylinder. I also have new front brake hoses and cannot find any leaks in the brake lines or connectors.

However, I did notice a very slow seepage from a plug in the bottom of the MC body. I have attached pictures. The main brake line connection going out the front of the MC is always clean and dry but the plug in the bottom is usually damp or wet. I tried to tighten the plug. It was already tight but I got just a little more on it without pulling too much. It still seeps. Is it "simply" a matter of removing the plug (and fluid) and resealing it? What is the proper way to reseal such a plug? Thank you.

Jon

 

[1 Wild R/T]

Looks to me like the fluid is coming from the top and dripping at the bottom... The whole M/C is wet... And fluid doesn't weep up, gravity makes it mostly flow in one direction...

 

[R413]

Yes above. Clean it with brake cleaner to get it dry and watch it close To see where the fluid is originating. Pump the pedal without moving the car so no sloshing in the reservoir, and see if any fittings are leaking.

 

[JonR]

Hmmm. Sorry I had not considered that. It could be the cover and gasket as with that other weeping post. Thank you for the suggestion. I will clean it and investigate further. If it's the cover, is it possible to replace the gasket with something compatible with brake fluid? I'm usually careful not tightening the cap bolt much to avoid cap distortion.

 

[pnora]

A leak always drips from the bottom never the top.

 

[1 Wild R/T]

A leak always drips from the bottom never the top.

Are Ya Sure? Maybe we need to consider people on the other side of the world.... @kiwigtx

 

[pnora]

Are Ya Sure? Maybe we need to consider people on the other side of the world.... @kiwigtx

Are those the guys with the reverse swirl toilets.

 

[1 Wild R/T]

I don't know how you'd keep fluid of any kind in a car like this....

 

[pnora]

I don't know how you'd keep fluid of any kind in a car like this....

View attachment 1485903

I would be more worried about the driver pooping his pants. At least here you can shake it down your leg.

 

[retractable]

I have had the same problem with that style of master cyl
My 66 Barracuda uses that too. I have a couple that I returned because the leak could.t be stopped. I started using a 64 fury master that does not have that plug. The original style of cap is much stronger then what you show in your picture and can be tightened more. I would try and find one.

 

[kiwigtx]

I don't know how you'd keep fluid of any kind in a car like this....

View attachment 1485903

Easy....have you never spotted the bung in the middle of the roof?

 

[JonR]

I have had the same problem with that style of master cyl
My 66 Barracuda uses that too. I have a couple that I returned because the leak could.t be stopped. I started using a 64 fury master that does not have that plug. The original style of cap is much stronger then what you show in your picture and can be tightened more. I would try and find one.

View attachment 1485921

Thanks! I sprayed it down real good with Brake Cleaner today so it is completely dry all over. I went in and pumped the brakes many times sitting here in the garage. It looks like there may be a little seepage now coming around the lid. I would like to find an original style cap - the one I have doesn't look good and it is weak. I could post in the parts wanted area. Is there any way to replace the gasket too - what material? Thanks. By the way, what is the purpose of the bottom plug?

 

[1 Wild R/T]

By the way, what is the purpose of the bottom plug?

Earlier vehicles used a pressure switch to activate the brake lights.. That was changed to a mechanical switch but the port is still there for applications that require it...

 

[Don Frelier]

I always suggest converting to a 67 and up dual chamber master cylinder.
It's cheap and easy to do.

 

[JonR]

At the moment, I'm fine with my single pot and the system is operating normally. Thanks. If I need to get in deeper I may change to the 67 dual chamber.

See the latest pics from today..............car has not been touched for 2 days since I cleaned the exterior of the master cylinder and pumped the brakes a few times. The brake fluid continues to wick down the sides a little more each day. The bottom plug is dry as you guys suspected. So, it's coming from the cover and gasket. I will try to find a better/stock cover but what about replacing the gasket? I could make one easily (a simple circle with a hole in the center for the hold down bolt) but from what material?

 

[Don Frelier]

Ok but a parking brake (which everyone calls an emergency brake) doesn't work very well to stop.
Try it at 40 mph and let us know.

 

[pnora]

At the moment, I'm fine with my single pot and the system is operating normally. Thanks. If I need to get in deeper I may change to the 67 dual chamber.

See the latest pics from today..............car has not been touched for 2 days since I cleaned the exterior of the master cylinder and pumped the brakes a few times. The brake fluid continues to wick down the sides a little more each day. The bottom plug is dry as you guys suspected. So, it's coming from the cover and gasket. I will try to find a better/stock cover but what about replacing the gasket? I could make one easily (a simple circle with a hole in the center for the hold down bolt) but from what material?

View attachment 1486609

View attachment 1486610

What does the top lip of the master look like? If its rust and pits no gasket will seal. Post a pic with the cover off. Also how full are you keeping it? To full is not good either. Also look that gasket over for age cracks. It could seal but if fluid is passing through it it will still wick out.

 

[MIKESPOLARA]

At the moment, I'm fine with my single pot and the system is operating normally. Thanks. If I need to get in deeper I may change to the 67 dual chamber.

See the latest pics from today..............car has not been touched for 2 days since I cleaned the exterior of the master cylinder and pumped the brakes a few times. The brake fluid continues to wick down the sides a little more each day. The bottom plug is dry as you guys suspected. So, it's coming from the cover and gasket. I will try to find a better/stock cover but what about replacing the gasket? I could make one easily (a simple circle with a hole in the center for the hold down bolt) but from what material?

View attachment 1486609

View attachment 1486610

I don't see where you can buy a new cover or gasket. From the looks of your master I would buy a new one so everything is new. Interesting enough, Rock Auto lists a Centric master for drum brakes that does not have that lower plug. Hopefully the one that get's sent out is the same as the picture.

 

[pnora]

NOS MOPAR 2401152 Master Cylinder Cover Gasket Fits 57-66 Models | eBay

 

[MIKESPOLARA]

NOS MOPAR 2401152 Master Cylinder Cover Gasket Fits 57-66 Models | eBay

$50 for a gasket. You can buy the brand new complete master