Brake Master Cylinder leaking problem.

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70DartMike

70DartMike

Too many projects
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Ok, a few months ago I installed front discs from a 75 Dart. I bought a new master cylinder for front discs. The problem I'm having is the seal under the lid of the master leaks like crazy. It drips down onto my inner fender, and as a result I've had to sand all the paint, and primer it to stop it from rusting. So I bought a new seal, cleaned the edges on the master really nice, cleaned the lid, put the new seal in, test drove it today and BAM it leaks even more now!! What do I do to stop the leaking? It is clearly running out of the lid, down the master cylinder, and dripping on my inner fenders and headers (well, onto my power steering hose, then on to headers). Please give suggestions. Am I supposed to get the edge of the seal wet with brake fluid before installing? Did I miss something? This is frustrating.
 
The lid looks to be fine. I'll go out and take some pictures of it. What I'm concerned about is the master cylinder itself. It appears to have some grooves in it from the factory? I bought it new so I'm confused.
 
Here are some pictures. I checked out the lid closely and it appears to be a tiny bit warped. Can I buy a new lid?

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Definitely your problem, the rebuilders get them in and just clean the lids up after being banged around in big bins.

The local parts stores usually only have the lids for the Chebby's. Check with your local junk yard, that style cover was used up into the late 80's on pickups and cars at least to the mid years. I don't have any spares right now or I'd send you one. A last resort the dealer should have or be able to get you one. Check the dealer clunker stock piles on the back lot for a PU or Ramcharger, you can probably talk them out of one.
 
Awesome, thank you very much for your help. I guess I'll be taking a trip to Joe's tomorrow. I would probably be better off anyways trying to find a used one from a car because at least I know it worked on that car. I might get another warped one if I buy it new.
 
As far as the grooves, looks more like dings and dents from getting tossed around. Imagine what what rebuilt stuff will look like in another 20 years with these go thru another cycle.

I save old originals and rebuild them myself, a little more work but they end up looking like new when done that way.
 
Do you think the grooves could be part of the problem? I hope not, I really don't have the time lately to change the master. I would have used the original from the disc donor car, but it was rusted beyond repair.
 
The gasket is there to compensate for those kind of flaws. Gasket and surfaces should be dry when you put it all back together too.
 
I am experiencing the same problem as well as many others. I have filed the top of the master cylinder and got it perfectly straight with no grooves or edges and I got a new cap and even went to the extent of using silicone around the top edge to seal it. I know I shouldn't do that but I wanted to see if I could stop the leak and it still runs down the side of the master. I think an upgrade to the aluminum master may fix it, I can't see why or how it could leak after being sealed. Good Luck and if you fix it let us know!!
 
Well, I fixed it, I found a straight lid from a 75 Cordoba or something in Joes field, but it was pretty rusty, as well was the rubber seal, but I cleaned the seal up because it is real rubber compared to the poly whatever that they sell now, and Joe figured it would seal better. The lid is straight, so I used it as well, and since then no leaking.
 
Thanks for the tip! I have the chrome master cylinder cover and rubber gasket that came with it. That may be the problem since most everyone on this forum thinks the chrome covers are junk.
 
I've got the same issue, after a good romp thru some twisties, no rear brakes. I also filed the top of the MC body and still leaks, even bent the "wire" snap a little to hold more pressure on the lid..still leaks, better but still leaks..never even thought it would be soooo simple (walks outside to check). Maybe I shouldn't park nose down the driveway anymore either.
 
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