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Brake lines are dry but no puddle underneath

Hello All,

A few months back I went to hop in my beloved '66 Mustang to run off down the road. When I hopped in, it started up great, and I pumped the brake pedal and on the second pump it went straight to the floor. Not a problem I thought, I’ll just look underneath and find the puddle and replace the leaking part, usually a slave cylinder. But there was no puddle!

Again no problem I though, I just put some more brake fluid in there and pump it until it came out of the leak then fix the leaking part. Well after a couple of months, I went and put the fluid in the master cylinder and then started pumping. Nothing came out. The level on the reservoir didn’t even fall. The fluid is now a milky rusty color.

How can I identify where the leak is at? Should I try and bleed the brakes till I find the location of the leak? Because I though if there is a leak in the system then it would essentially bleed the brakes through that hole.

Thank you for your help.

Maybe it’s time to replace the entire brake system from one end to the other…Master cylinder, wheel cylinders, flex lines and probably the hard lines too…

The cord structure of flex-lines can rupture, allowing the rubber jacket to expand and contract like a balloon, the brake pedal going to the floor but no visible leaks…

Other ideas.
Look to see if the fluid could be leaking to the rear of the master cylinder unit. That could be along the engine firewall, underneath the dash by your feet, or maybe even into the power booster unit (if applicable).

Sounds like a bad master cylinder, but caddyman is correct about the rubber lines. Sounds as if the fluid needs to be flushed too. JoeMario is correct with a leak in the power booster. Also, the leak could be in the wheel drums and you not see it.

Well I just got back from underneath the car. I looked again at the wheel cylinder on the rear passenger and I think I see signs of a small leak.

I also think I will swap out the master cylinder too after seeing all the rust and after reading these comments. I didn’t see any leaking, but I might look inside the vacuum power boost, I didn’t think about that.

The thing is: I rebuilt the whole brake system (minus the brake lines) 10 years ago… wow now that I say that out loud it sounds like a long time ago, dang what happened there. SO I guess it is getting old. So I guess I’m fixing to do a little over haul on the whole thing. So much for the simple fix.

How often do you drive this car?

I’d guess this is a bad master cylinder. First replace that & see if it fixes the entire problem. You may find you next need to replace one or even all the wheel cylinders. (Assumng all 4 wheels are drums.) And I wouldn’t be suprised if you may find the flexible rubber brake lines need replacement too.

But start with the master cylinder. If you do it yourself, be sure you follow the instructions exactly which come with the new one. Many brands of master cylinders – to work correctly – need to be bench bled first, before putting them on the car.

I used to drive the car everyday, but not so much anymore. But I’m going to swap out the master cylinder and that one wheel cylinder I looked at earlier. and new break pads too. I bought the cheapest master cylinder 10 years ago, I think this time I am going to buy a nicer one.

Well it turns out all you internet people where correct! Here are some pictures after I removed the master cylinder. As you can see there appears to be a pool of dried, semi dry goo left over from a leak on the master cylinder.