Brand New Master Cylinder Leaking?

[65Vart]

I just replaced a master cylinder that was leaking at the lid. I needed to be replaced rather than just replace the gasket and at 125.00 no big deal. Took the car out and I’m still seeing brake fluid along the bottom of the new master. This is a 340 power brake car. Very frustrating. Any ideas? Cant find a leak source.

 

[67Dart273]

I hate to depress you but I've said this many times. I have about 14 years, in a previous life, in auto parts, and BEFORE the current nonsense of all china, all the time.

"New" does not mean good, or functioning, or high quality.

I come from the days of Raybestos, Wagner, and Bendix. But even back then, rebuilts could be suspect, and even new, once in awhile, had problems.

 

[65Vart]

I hate to depress you but I've said this many times. I have about 14 years, in a previous life, in auto parts, and BEFORE the current nonsense of all china, all the time.

"New" does not mean good, or functioning, or high quality.

I come from the days of Raybestos, Wagner, and Bendix. But even back then, rebuilts could be suspect, and even new, once in awhile, had problems.

Thanks, I thought the same thing.

 

[65Vart]

Anybody else? Any ideas

 

[340sFastback]

I have had master cylinders where the cast iron body where the lid seals is rough and porous like. Those leaked no matter what I did. I ordered a couple off rock auto for '73 power disc brake Duster 15/16 and was able to get New not rebuilt. On ones I got the sealing surface is smooth allowing lid to seal to body of master cylinder. I run with brake fluid level around 1/4 inch down from the top too.

 

[volaredon]

Preaching to the choir

 

[matthon]

Take it off, flip it over on some sandpaper on a flat surface, metal or even glass works.
Sand it until it's smooth, then sand some more. Once done, sand some more, then repeat.

 

[67Dart273]

Or if you know someone with a mill or mill drill you can run it through there and mill it flat. Clean it up/ out really well.

I would also examine the gasket and lid closely for roughness and the lid for warped. Small straightedge inside

 

[67Dart273]

The thing is with this day and age of import junk, you might have a whole run of them with the same casting defect

 

[Cal Tonsley]

I had a similar issue with a new master cylinder, kept on finding fluid on the base while I was restoring the vehicle, I tried a lot of things to solve the problem, mainly lines and flares thinking that I must have messed up when I made the lines. In desperation one day I pushed my iPhone under the cylinder and took some photos (attached) Turned out that there was a fine casting flaw / crack in the base. Unfortunately new doesn’t necessarily mean perfect or fit for purpose!
Hopefully my story might help you solve your mystery!