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Discussion Starter #1
Hi everyone,

66 Mustang coupe, 289/auto, factory disc brakes up front, rear drums.

So I've had the car fully up on jack stands for 3 or 4 months doing some work to the rear and suspension, but haven't touched the braking system at all. Finally got finished everything I was working on, lowered it back to the ground with the wheels on and... no brakes. Pedal went to the floor. I checked the master cylinder and it's practically empty.

Something had to be leaking right? So I go check all 4 brakes, they're all bone dry. Checked under and around the master cylinder, booster and distribution block... bone dry. Where the heck did the fluid go? Prior to any of this I had braking but it was always kind of spongy even with the disc brakes up front.

So I refilled both bowls and proceeded to bleed the brakes. Did the rear right and rear left no problem, finally got some pedal back. Bled the front passenger side and lost all pedal. I notice now when I depress the brake pedal with the cap off the MC, I get bubbles from the main bowl, and fluid actually squirts out of the secondary front bowl. With the cap on fluid actually leaks past the seal on the cap. It's my understanding that the fluid shouldn't really be sloshing around in there, right?

Any idea about what's going on??
 

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I would think that if the master cylinder was bone dry that you would have to disconnect the brake lines to it and bleed it first, then reconnect the lines and bleed each wheel individually.
I had an issue with my distribution block.
The small valve piston inside of it has a couple of "o" rings that were old and brittle.
The brake fluid was leaking past them and coming out of the brake pressure warning light switch that was screwed into the top of the block (plastic).
The brakes are still ****** though (drums all the way around) so I'm anxious to see what some of the other replies will be.
Good luck.
 

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Do you have power brakes? If so check the booster. A leak in the MC rear piston will leak into the booster.
 
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I don't think the '66 dist. block has those 0-rings like the later years does.

Fill the bowl, Leave the cap on. Bleed the brakes starting with the rear right, rear left, front right, then front left. After every wheel check the fluid level. You WILL SEE a leak somewhere if there is a leak. You're right, that fluid is going somewhere. Don't be concerned with geysers of brake guild inside the m/c. But fluid coming out of the m/c top gasket is not right. No geyser should be causing a leak. Is the lid on tight, or just sitting there ?

Z
 

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All caps should seal MC air tight, as brake fluid can absorb moisture which lowers its boiling point. The caps should have a rubber type membrane or bellows so that as fluid is used, the bellows can move. Since all of the fluid was gone, I am assuming you have a single chamber MC like came on the the 66, when the MC leaks it will leak inside the car on the firewall, sometimes it will leak on the firewall in the engine compartment. If you have not replaced all the steel brake lines, they could be corroded in the tunnel by the driveshaft, that's where mine were leaking on my 65. Gravity brake bleeding does not always remove the air as the fluid must run out faster than the air bubbles can rise, you will either have to have someone push the brake pedal while someone does the bleeder valves or use a pressure bleeder on the MC, in the old days we used a fitting on an old MC cap, with a hose attached it to a tire inflated to 10 psi, and it actually worked well. My 2 cts. Good Luck.
 

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Discussion Starter #6
Thanks for the replies everyone, haven't had a chance to touch the car all week.

It's a dual-bowl master cylinder, and the cap was on tight when I checked it and discovered almost no fluid. The distribution block is literally just a block of brass with 4 ports, one is plugged and the other 3 have brake lines going to them... no leaks there. The MC wasn't bone dry, but nearly there. I didn't get to look inside the firewall yet inside the car, but the floor all around the car is completely dry. Nothing leaking at the wheels or in the master cylinder area.

When bleeding I did have the cap on tight, but fluid was still oozing out past the seal all around it. If it's supposed to be air tight then I guess the seal is worn out. I only checked it that one time with the cap off as someone slowly pressed on the pedal to see what it was doing. Just out of curiosity I left the front brake bleeders open with the front end raised and the MC full, and zero fluid has come out of the bleeders all week. Would a vacuum bleeder be more efficient?

I'm wondering also if I should swap out the current booster/MC for a later model one.
 

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I certainly don't have all the answers on this one, but I can say for sure that if you open a bleeder valve fluid should start coming out, right then. while a vacuum bleeder tool is useful, you shouldn't need one just to get the fluid to flow. A pinched line, or plugged up line, or collapsed flex hose are things to be checked. Can you get some compressed air to see if the lines can be blown out ?

Of course, none of this helps you find the leak. Gotta be one somewhere.

Z
 

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Discussion Starter #8
I certainly don't have all the answers on this one, but I can say for sure that if you open a bleeder valve fluid should start coming out, right then. while a vacuum bleeder tool is useful, you shouldn't need one just to get the fluid to flow. A pinched line, or plugged up line, or collapsed flex hose are things to be checked. Can you get some compressed air to see if the lines can be blown out ?

Of course, none of this helps you find the leak. Gotta be one somewhere.

Z
Thanks, I'm going to see what I can get done this weekend. I'll start by looking for leaks and try bleeding it properly again front to back. There has to be something funny going on
 

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Thanks for the replies everyone, haven't had a chance to touch the car all week.

It's a dual-bowl master cylinder, and the cap was on tight when I checked it and discovered almost no fluid. The distribution block is literally just a block of brass with 4 ports, one is plugged and the other 3 have brake lines going to them... no leaks there. The MC wasn't bone dry, but nearly there. I didn't get to look inside the firewall yet inside the car, but the floor all around the car is completely dry. Nothing leaking at the wheels or in the master cylinder area.

When bleeding I did have the cap on tight, but fluid was still oozing out past the seal all around it. If it's supposed to be air tight then I guess the seal is worn out. I only checked it that one time with the cap off as someone slowly pressed on the pedal to see what it was doing. Just out of curiosity I left the front brake bleeders open with the front end raised and the MC full, and zero fluid has come out of the bleeders all week. Would a vacuum bleeder be more efficient?

I'm wondering also if I should swap out the current booster/MC for a later model one.
Brake parts are cheap relative to not having them fully operational when needed. I suggest that you just rebuild the hydraulic system, new booster, master, all new lines. Wheel cylinders and calipers are easy to rebuild but also cheap to replace. And replace the brass distribution block with a new proportioning/ combination valve.
 
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