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Hey guys,

When a master cylinder starts leaking internally with power brakes, does the brake fluid run down the firewall and drip on the floor OR does the fluid leak into the power booster and get sucked into the engine by the vacuum line?

I've got a case of disappearing brake fluid and I'm trying to figure out what is going on.

Phil
 

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Hey guys,

When a master cylinder starts leaking internally with power brakes, does the brake fluid run down the firewall and drip on the floor OR does the fluid leak into the power booster and get sucked into the engine by the vacuum line?

I've got a case of disappearing brake fluid and I'm trying to figure out what is going on.

Phil
First lets get some terminology straight. If a master cylinder leaks internally, it is bypassing and no fluid loss would be noted, just unable to build correct pressures. If master cylinder leaks externally, then it is from either the end seals or the seats for the lines. Since it is pretty easy to see if the lines are leaking, let's assume those are ok. Easiest way is the unbolt master cylinder from the booster and slide back to see if the booster or end of the master cylinder is wet. You do not need to remove the lines if there is enough length in them to bend a little.
 

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When the master cylinder in my '72 leaked, it ran down the front of the power booster. I replaced it before I experienced any other symptoms!
 

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Mine leaked into the booster for a while before I noticed it. Eventually it ruined the diaphram in the booster and I had to replace both.
 

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Not to hijack the thread, but is there any way of telling if any gets into the booster? I have been hearing weird noises from that area when I drive, but the brakes work fine (for now).
 

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what wilit said.....exactly what mine did, eventually started dripping on the drivers side floor...pull the vacuum line from the booster and plug it with your thumb, see if the engine runs better, if it does your diaphragm is shot, mine was bad and driving the car every day I didn't notice it, what a difference after I replaced it!
 

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I have pulled the vacuum port off the booster and dipped whatever was handy down in there to see if it came back out wet. One time I found about a pint of fluid in the booster and used a suction gun to draw the brake fluid out. I then sprayed alcohol all in it to rinse it then drew that back out too. With a new master cylinder the booster seems to have survived, that was about two years ago. It wasn't a Ford, but the same thing can happen on many vehicles.
 

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Discussion Starter #8
I have pulled the vacuum port off the booster and dipped whatever was handy down in there to see if it came back out wet. One time I found about a pint of fluid in the booster and used a suction gun to draw the brake fluid out. I then sprayed alcohol all in it to rinse it then drew that back out too. With a new master cylinder the booster seems to have survived, that was about two years ago. It wasn't a Ford, but the same thing can happen on many vehicles.
Hmmm...

Kind of my worst fear.

Guess I need to do some more investigating. Guess I know what I'll be doing tomorrow.

Thanks guys!

Phil
 

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Discussion Starter #9
Well I took my '67 style dual reservoir master cylinder loose from the Trans Am racing booster and I couldn't see any brake fluid in the space between the two. I also took the vacuum line loose from the intake manifold and held it down to see if it had any brake fluid in it. Dry as a bone.

However, I did note that while I had the master cylinder cocked back at an angle, some fluid dripped out around the cap. The cap gasket is in poor shape and is definitely allowing some fluid to leak out (during cornering/acceleration/decelleration). I don't know if that could be significant enough to cause the car to leak an ounce of brake fluid out every few months, but it's all I saw so I've ordered a new gasket.

Most of the fluid disappearing has been out of the rear brake section of the reservoir.

I've checked the rear brakes and the lines leading to the rear brakes and I can find no leaks.

I'll replace the gasket and continue to monitor.

Phil
 

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If it's gone out of the rear resevoir, it's time to pull the drums and look. A wheel cylinder can leak a little and make a big mess inside the drum without ever actually dripping out of the brake assembly. But if you have 4 wheel disks on that thing, nevermind.
In my case, the vacuum line to the booster never drew up any fluid, it all just puddled in the bottom of the booster. Hence me having to use a "dipstick" to find it.
 

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Most of the fluid disappearing has been out of the rear brake section of the reservoir.

I've checked the rear brakes and the lines leading to the rear brakes and I can find no leaks.
Don't forget that the rear reservoir is usually plumbed to the front brakes and vise versa.

Dave
 
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