Weeping Master Cylinder Plug

[JonR]

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

It looks pretty decent - see first pic. I usually keep it 1/4" from top per Service Manual. The last three pics are (1) cover & gasket as taken off, (2) cover and gasket separate as removed, and (3) cover and gasket with gasket flipped over. The gasket is a rather substantial looking fiber material and does not seem to have any cracks around the edge. And, yes, I'm not spending $50 for an NOS gasket though I do appreciate the link!

 

[JonR]

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.

I might eventually just replace the whole MC but really this one does not look that bad as you can see from the cover off pic below. Heck I could just rebuild it if I find that the bore is good.

 

[1 Wild R/T]

That top gasket surface is never gonna seal.... Those pits act like a channel allowing fluid to wick past...

 

[moparx]

you could always try some JB weld "gas tank" sealer, but you might have a hard time getting the lid off for the next fluid inspection........

 

[dadsbee]

Drain the fluid.. suction pump.. syringe or siphon. Pack the reservoir with shop towel. Wrap a piece of 120 sandpaper around a wood block and make the rim flawless. Clean the seal with brake kleenex till it's spotless. Refill and reassemble with fluid 1/2" below edge.

 

[moparwacko]

^^^^^^ this.
And......I also replaced the MC on my 64 D100 just to get it on the road. I had to remove that lower plug 3 times and reseal with a new plug to get it to stop seeping.
And, the top still leaked, but gave up and went to my stash of O rings and voila, no more leak. DO NOT OVERTIGHTEN THE LID.
All this is great, but will be doing a front disc conversion over the winter to end it all.

 

[JonR]

Drain the fluid.. suction pump.. syringe or siphon. Pack the reservoir with shop towel. Wrap a piece of 120 sandpaper around a wood block and make the rim flawless. Clean the seal with brake kleenex till it's spotless. Refill and reassemble with fluid 1/2" below edge.

That's an excellent idea. The top surface is "not bad" but certainly not spotless. I did clean as much as I could, flattened the gasket and flipped it over. Then I tightened the cover more than I usually do. Still seeping from top edge but much slower than before. Until I'm ready to take your approach maybe I'll just clean it with Brakleen every so often.

 

[JonR]

^^^^^^ this.
And......I also replaced the MC on my 64 D100 just to get it on the road. I had to remove that lower plug 3 times and reseal with a new plug to get it to stop seeping.
And, the top still leaked, but gave up and went to my stash of O rings and voila, no more leak. DO NOT OVERTIGHTEN THE LID.
All this is great, but will be doing a front disc conversion over the winter to end it all.

Now, at least I think the bottom plug is OK. It's coming from the cover. I'll look for a proper sized o-ring! I did tighten it more than I'm comfortable with so I will back that off a bit. Thanks.

 

[moparx]

I'm just throwing this out there as something to ponder.........
Does your local hardware or home improvement place have a selection of O-rings for hydraulic/farm/implement uses ? that may be a place to check.
I'm guessing you would need something with a cross section width of about 3/16 or 1/4" that fit your cap snugly at the bottom to seal.
Or a "flat" style ring [around here, we call then "tetra-seal" rings] that fits the cover and overhangs the bowl a little, around 1/8, 5/32, or 3/16" thick.
If going this route, don't forget to use a sealing washer or o-ring on the retainer bolt of the cover. [if so equipped]

 

[JonR]

I'm just throwing this out there as something to ponder.........
Does your local hardware or home improvement place have a selection of O-rings for hydraulic/farm/implement uses ? that may be a place to check.
I'm guessing you would need something with a cross section width of about 3/16 or 1/4" that fit your cap snugly at the bottom to seal.
Or a "flat" style ring [around here, we call then "tetra-seal" rings] that fits the cover and overhangs the bowl a little, around 1/8, 5/32, or 3/16" thick.
If going this route, don't forget to use a sealing washer or o-ring on the retainer bolt of the cover. [if so equipped]

Thanks for the advice. I will try to find a suitable o-ring. Tractor Supply has some odd farm hardware.

 

[moparx]

please let us know how you make out.

 

[JonR]

please let us know how you make out.

I will. So far I have cut down the seeping quite a bit by lightly cleaning the MC surface, cleaning and reversing the gasket, and tightening the cap a bit more than I had. Still some seeping.

 

[retractable]

This is the master without the bottom plug
Just received from NAPA.

 

[JonR]

This is the master without the bottom plug
Just received from NAPA.

View attachment 1490980

View attachment 1490981

Thanks very much for posting. I will take note of that and may pick one up to have on hand. How much was it?

 

[matthon]

If keeping the old, or even putting a new mc on, put sandpaper on a flat surface, I've used a piece of metal on a workbench or even glass in the past, flip the mc over onto the sandpaper and sand it until it is smooth, then sand it some more.
Clean the cap and mc inside and out.
Get a roll of gasket material and cut out a new gasket, put it over the old one.

I have never had a cap leak after doing this, new or old mc, cause new ones right out of the box can leak too.

 

[JonR]

If keeping the old, or even putting a new mc on, put sandpaper on a flat surface, I've used a piece of metal on a workbench or even glass in the past, flip the mc over onto the sandpaper and sand it until it is smooth, then sand it some more.
Clean the cap and mc inside and out.
Get a roll of gasket material and cut out a new gasket, put it over the old one.

I have never had a cap leak after doing this, new or old mc, cause new ones right out of the box can leak too.

Make sense. I had asked earlier in the thread if the gasket needs to be of a particular material. So regular fiber type gasket material should work. I may try the O-ring option too just to see. Thank you.

 

[retractable]

New NAPA Master cyl. $154.00
They had rebuilt also.
Power brakes ones are cheaper but they don't have brake rod. The brake rod can be switched if you have the rubber part that keeps the rod in the plunger part


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