Brakes Brake fluid disappearing?

opihinalu

Active Member
Feb 10, 2021
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Florida
I gutted my proportioning valve and I replaced it with an adjustable one and it worked well for a few test drives (no leaks) and then I let my car sit for a couple months while I worked on it more. I glanced over at my brake fluid and it was obviously lower than it was before. Today I looked again and it’s almost empty. I haven’t driven the car. I checked all of my work and it isn’t leaking from anywhere. Is it possible for brake fluid to leak without and driving or any compression of the brakes? Anyone have any ideas?
 
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limp

wrap a little cheese around it and its a done
Oct 4, 2020
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When you can't find a leak anywhere, its usually the Master Cylinder leaking into the booster which is then being burned in your engine, which is why there is NO evidence of leaking
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Yup. It's leaking somewhere.

Brake fluid doesn't really evaporate. If anything it absorbs moisture so your level should actually rise if you left the system open.


Like limp said, back of the MC into the booster is a common spot if you don't see any leaks out on the wheels or lines
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Two places to look for fluid leaking into the booster
Under the master cylinder traveling down the booster or more likely (since you see no evidence of a leak) into the cabin beneath the carpet, pull the carpet back from under the brake peddle.
 

opihinalu

Active Member
Feb 10, 2021
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Florida
Two places to look for fluid leaking into the booster
Under the master cylinder traveling down the booster or more likely (since you see no evidence of a leak) into the cabin beneath the carpet, pull the carpet back from under the brake peddle.
Yup. It's leaking somewhere.

Brake fluid doesn't really evaporate. If anything it absorbs moisture so your level should actually rise if you left the system open.


Like limp said, back of the MC into the booster is a common spot if you don't see any leaks out on the wheels or lines
When you can't find a leak anywhere, its usually the Master Cylinder leaking into the booster which is then being burned in your engine, which is why there is NO evidence of leaking
Thank you guys for the super helpful info. Well check this out tomorrow.
 
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