Brake master weeping

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stackattack

stackattack

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So again I am kneeling before the FABO gods for aid with my Mopar. So after a cruise for about an hour, I noticed the brake getting a little more "travel" before stopping and the pedal getting a bit spongy. When I parked in the garage i noticed some smoke and low and behold the master is weeping some fluid onto the exhaust headers. The cylinder is a two bowl. I have discs on front and drums on the rear.

So, initially I thought maybe the clip on the cylinder was just old and loose so i pulled it off and did some bending on it to try to tighten it up. I noticed the smaller front bowl was low and appeared to be what was being forced out. Topped off and back out to test. Still weeping some but not as much.

In my case the small front bowl appears to be connected to the rear drums and the larger rear bowl is connected to the front. These lines have been replaced years ago by previous owner, but I thought that generally the smaller bowl went to the rear? Or is based on which has the drums vs. discs that matters?

With that in mind I am trying to ensure that the right feed lines are going to the right brakes and also then determine why it is pushing out at the cylinder lid. I have gotten under it and found no leaks in lines or running down wheels, etc. Before I put my viking hat on and begin screaming and warrior crying at the rear drums to remove them I figured I'd consult the gods...
 
Disc masters have a large bowl and a small bowl. The large bowl is for the disks. As pads wear out, the disk piston rides closer to the rotor to compensate for the wear. This makes the "hole" behind the piston bigger, and is filled with fluid. So in essence, fluid is replacing the volume of pad wearing away. That's why you need more fluid.

Check the joint between the master cyl and the booster (PB), or Firewall (MB). Sometimes fluid leaks past the master cylinder piston.
 
M/C lids are prone to leaking. Rubber gasket gets old and hard, so doesn't seal as well. Replace rubber gasket if you can find one, and draw file the top to flatten.
 
A lot of guessing here. Fill reservoir with fluid and cap. Clean around brake area including rear of master cylinder with engine gunk and let dry. Take car out for a drive and brake hard a few times and return. Now take a clean and dry paper towel and wipe all around and you should find the leak. Also check the PP valve for leaking on the exhaust, same above applies.
 
I had pretty much the same problem with my 70 Dart with the K-H disc brakes. Master cylinder was always wet and fluid low. I tried making the spring clamp tighter, replaced the gasket with an NOS one that I had, but it was always wet. I even tried lightly sanding the top of the master but no difference. I finally emailed Richard Ehrenberg of Mopar Action about this problem. His response was immediate and straightforward, the cylinder is defective and must be replaced. Once I replaced it, no more problems with leaking.
 
missing linc said:
I had pretty much the same problem with my 70 Dart with the K-H disc brakes. Master cylinder was always wet and fluid low. I tried making the spring clamp tighter, replaced the gasket with an NOS one that I had, but it was always wet. I even tried lightly sanding the top of the master but no difference. I finally emailed Richard Ehrenberg of Mopar Action about this problem. His response was immediate and straightforward, the cylinder is defective and must be replaced. Once I replaced it, no more problems with leaking.
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Funny you should mention a defective MC. I have heard of people installing the cups in backwards, which would force the fluid up and not down the lines, but I'm sure you would notice the brakes not functioning.
 
I have often found that seepage at the M/C is being caused by an excessive return of fluid to the reservoir.
Less often occuring when the rear shoes have excessive travel (pedal was mentioned) and the springs pull the shoes a LONG way back.
Most common is air in the affected system compressing like a spring, and when you release the pedal, the fluid forcefully returns to the reservoir, blasting against the rubber seal.
Easy enuff to check,.
Set the emergency brake. This moves the rear shoes into contact with drum, and when you pump the brakes, the w/ cyl will fill and push the pushrods out to the shoe.
The rear wheel cyl cannot create any reverse pressure with the emerg on.
Have someone pump the brake pedal a couple times, and hold it down.
Remove the cap, and have the pedal released, and watch the reservoir .
There should be very little disturbance in the large reservoir (disc).
There should be more disturbance in the small, - if you have a strong return or geyser/fountain into the small (rear) reservoir there is air in that system.
(Remember the rear cyls can't push back).
Getting rid of the air/spring will often resolve the weeping .
The seal is to stop sloshing, not a forceful blast of fluid.

BRAKE fluid is excellent paint remover, so protect and thoroughly rinse with water, any fluid splashed on the paint ! ! !
 
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Swinger 340 said:
Funny you should mention a defective MC. I have heard of people installing the cups in backwards, which would force the fluid up and not down the lines, but I'm sure you would notice the brakes not functioning.
Click to expand...
My brakes always worked excellent. minimal pedal travel, car stopped as it should have, the only issue was the constant leakage. The calipers were fresh, as were the rear cylinders, all of pads, shoes, the lines and hoses were new, even the master itself was a rebuilt one, installed when I did the disc conversion. It had sat on the shelf for a couple of years, but was still dry and in the box so I did not believe that should have been an issue.
 
I was just shopping for a new master cylinder for my 70 disc brake setup and a weeping master was listed as one of the signs of a failing master cylinder on their website. Oh yeah mine's been weeping for years and I also tried many of the mentioned fix's
 
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