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  #1  
Old 12-26-2014, 09:45 PM
ramos291 ramos291 is offline
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Default mystery disappearing brake fluid

Ok so I thought it was a strange thing that my brake fluid was empty one time. There were no leaks at the wheels or anywhere else that I could see. Then It happened again and yet again this year. It didnt become empty instantly but over time. Any ideas where it might be going? Might it be going into the vacuum line, brake booster, evaporating,?
I do want to replace the master cylinder and brake booster but I have no clue what one to use.
Thanks for your input.
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  #2  
Old 12-26-2014, 09:55 PM
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If you don't see any visible signs of a leak then most likely it is leaking into your booster. You can remove the two mounting bolts on the master cylinder and pull it out slightly from the booster. If you see any brake fluid at all on the rear of the master cylinder or on the push rod then that's your problem. You can replace the single master cylinder with a dual master cylinder from a late 60's Mustang if you want to go with a safer setup. You will just have to split the lines front and rear. The stock single master cylinder is rather easy to find.

John
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Old 12-27-2014, 02:18 AM
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John is right. A booster will hold a lot of brake fluid before it fills up to the vacuum hose. Brake fluid is not oil-based, it's glycol based and it won't burn. If you see funny looking smoke that periodically comes out your exhaust, it's probably brake fluid.

For this to happen, your Master Cylinder's piston seal leaks and your booster seal leaks as well. When you get it fixed, you will notice a big difference in your braking. - Dave
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Old 12-28-2014, 03:40 PM
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Thanks so much John.
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Old 12-28-2014, 03:43 PM
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Thank you Dave for the response and great information.
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Old 12-28-2014, 08:59 PM
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John, I have been looking on Rock Auto for a replacement master cylinder, so many to choose from and there is also the issue with those being for ft disk and rear drum. Does that matter because my bird is all drum at this point?
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Old 12-28-2014, 09:17 PM
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You want a drum/drum master cylinder for power brakes. The Cardone numbers are 101488 or 131488. They are listed under 1968 Mustang. The only issue you may have is with the shock tower to firewall strut. You may have to raise it to clear the master cylinder top.

John
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Old 12-29-2014, 04:51 PM
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Thank you for the Cardone numbers and warning about shock tower firewall issue.
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Old 01-27-2015, 07:46 PM
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I have installed the new dual master cylinder, connected it to a proportioning valve, bleed brake line and so forth. However, when pressing on the brake peddle, engine running, the idle speed increases and becomes rough. let go of the peddle and idle smooths out. Also when testing the braking in short spurts on the drive the peddle seems hard and takes a good amount of effort to stop the car. The new master cylinder is for a 68 mustang and did not come with a new plunger rod so I used the old one I had with the old single master cylinder. The vacuum lines also seem ok and the brakes before the switch to a dual also seems good. I find it hard to think the brake booster would just go bad after the switch when it was ok before. The booster had a good amount of brake fluid in it and that is why I changed it out. I did suction out the fluid before installing the new master cylinder. Any thought, suggestions, prayers to help? I am lost on this.
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Old 01-27-2015, 07:57 PM
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You obviously have a vacuum leak related to the brake booster or check valve. The master cylinder and prop valve have nothing to do with losing vacuum. It's possible that the rod is too short for the new master cylinder and you are forcing the booster to go past it's limits when you push on the pedal. That's the only thing I can think of.

John
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