Brakes - Master Cylinder Leaking

[dtedler]

Guys I need some advise. I had a leaky master cylinder on my '73 Challenger and I replaced the master cylinder. I drove the car to St. Louis this past weekend and notice the master cylinder was again dripping with fluid. All the fitting are tight and not leaking, however the entire bowl casting is wet. What is going on. I need your recommendations before I go tearing into stuff, again.

Thanks - Tony

[dwc43]

Is it leaking from the cap and running down? You may be over filling it and when the rotors kick the piston back it leaks, or you could have a caliper sticking causing it to heat up and boil the fluid out.

[dtedler]

It is leaking from the cap and running down - Yes. When I went throught the brakes this spring, I replaced both calipers, however, I did not replace the lines, which where replaced two years ago, when I worked on the suspension. A stuck wheel cylinder in the rear - could this cause the boiling of the fluid. I'm guessing that one of the flex hoses are collapsed inside.

[dwc43]

IT could be a bad line as well. I kinda doubt it's in the rear, but you never know.

[John Kunkel]

When the fluid was running down the casting did you remove the lid and check the fluid level in both reservoirs?

A lot of leaks at the cover are a simple case of a bent lid, faulty gasket, etc.
Even with the proper fluid level fluid will slosh past a bad lid seal.

[dtedler]

I'll check this evening - Thanks

[MoparBrew]

When I put hedders on my 73 Cuda I must have had old brake fluid in the master, the heat from the hedders made the fluid boil/flow right out of the resevoir similar to your problem. I had to rejet the carb and put in Dot 4/5 brake fluid and problem was solved.

[rrunnertexas]

I am having the same problem with my master cylinder leaking from the gasket area. It is driving me crazy! I am using a mid-70s style factory master cylinder with my disc brake conversion.

In an attempt to correct the problem I replaced the master cylinder gasket, lid and tension wire. Nothing changed, just lots of leaking.

Next, I used a file to create a flat, clean mounting surface for the gasket. A slight improvement, but still leaking!

I could use some good advice as to what to try next.

Thanks!

[ehostler]

Read this entire thread. There are several ideas in it, that you did not try.

[Steve Barracuda]

I have ran into this problem many times and the leaks are usually from the lid and usually with reman master cylinders. A new Wagner or Raybestos master should cure the leaks , if that fails then the new style plastic resovoir master will definately stop the lid leaks .

[rrunnertexas]

Steve Barracuda.....

That brings up another question... What is the difference between a new and rebuilt unit? (I know, one is new and the other is rebuilt - ha!)

Seriously, is there something different with the mating surface on the top where the gasket meets the cylinder? Do new cylinders have a smooth gasket surface vs the rebuilt units "as cast" type surface?

Also, when the lid is on and sealed and the brakes are depressed, is there a pressure or vacuum in the reservoir that would cause the fluid to be pushed out?

I have considered the newer style master cylinder... but, I like the old style iron style for it's looks. Of course, if I can't get it to stop leaking it may be in the trash bin.....

[dwc43]

There's no real diff. between new and rebuilt. You just run intop lids that have been warped or dropped and bent at times. Not something that they look at too close. All they are interested in is the internals.

[cageman]

Take the lid off and press the pedal, then let go, watch what the fluid does, and then you will see why the thing will leak if the seal is not good, it is like a little fountain in there.
Plus, what goes out, can alos get in, like condensation or water when getting a bath, and that kills brake fluid. Brake fluid will pull moisture out of the air.