The master cylinder on my '75 Scamp leaks.

The front resevior will pump itself dry, you can see the fluid has run out from under the lid and gasket. The rear doesn't leak a drop.

The car is equipped with front disc brakes.

Any ideas on what could be causing this?

gravity generally pulls things down, not up, so i dont think fluid is running out of the top of your master cylinder. is the bail holding the cap tight against the body? if not, the master may start collecting dust and getting damp, but if it is pumping itself dry it is leaking out elsewhere. throw some cardboard under your car and hold your foot on the brake a good long while, the leak will present itself.

check the inner sidewalls of your tires for streaking. pull wheels and drums and check for dampness at all four corners. your calipers, backing plates and the insides of your wheel cylinder boots should all be dry.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

There is no apparent leakage around the rear wheels or lines. I have not taken the drums off yet...was going to do that tomorrow if I get the chance...

You can see the fluid all over the front of the master cylinder and where it drips down onto the steering column...it is leaking out of the lid...Its like it is getting pumped out of the master cylinder through the lid...

The lid is tight, but it still manages to squeeze out of between the gasket...

The front brake system doesn't lose any fluid.

Check the inside of the firewall under the dash. My bet is it’s leaking out the back, running down the firewall till it hits the column, then runs into the engine compartment to drip off.

Danny

Could he have a Blocked rear line???
Just a thought.
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

How about a hardened rubber gasket?

If it is definitely coming from around the lid, then either the gasket is hardened, crusted with rust, or perhaps even the lid is bent. Does the wire holding the lid snap firmly in place? If you set the lid onto a flat surface, does it sit perfectly flat?

I think I would start with a new lid gasket, and go from there.

If you had a blocked rear line I would think the pedal would be hard to depress and have very limited travel.

-Mac

The gasket is still supple on the lid..the lid itself doesn't appear bent and the wire snaps pretty tight...

The master cylinder also has rust lines down the front from fluid running down it for so long...

I need to replace the rubber lines since they are a bit dry rotted...so I'll check the rear brakes to see if I can see anything else suspicious...

The strange thing is that I had this same problem though not as bad with my '57 Plymouth that I upgraded to front discs...but one day it mysteriously stopped and now works perfectly...and doesn't leak a drop.

Both cars have the exact same master cylinder too.

What does the sealing surface on the top of the MC look like? Any pitting? Maybe a crack in the reservoir?

Just some ideas,

Nat

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

Surface has some minor roughness...nothin major.

I bent the clamp a bit tighter..I'll see if that makes any difference..

I checked the rear wheel cylinders and there was some brake dust collected around it but no major leakage at all.

No leakage behind the master on the interior either..

Many years ago I had an MC start to slowly pump from the rear to the front reservoir - the front one would overflow, while the back lost a little, but other than that was fine... some kind of internal MC leak. A a temp fix, I put a paperclip to hold up the gasket and allow the front excess to refill the back, and that worked until I replaced the MC.

i got the same exact problem on my 73 scamp. Its a remanufactured master cylinder that i put on about 2 months ago. everything clips on tight, but it doesn't seem to seal. I tried bending the clip, sealing the gasket, everything. It's probably something in the master cylinder itself. Mine is a reman. I actually jb welded the edges of the gasket, and that seems to have stopped the leak. I'm pretty sure it fixed the wrong problem in my car, but with limited funds, its the best i can come up with. Have you rotated the lid 180 degrees? if its the gasket, itl'l then leak out the other resevoir. and btw, this is a quick fix. it stopped the leak, but probably not the problem.

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