disappearing brake fluid

[abcus]

I tried to find a thread on this, but I am not good on the computer. When I checked the master cylinder it was low.I do not see any brake fluid under the car. The pedal holds up when I push on it.

[GeneralDisorder]

Which vehicle is this concerning?

 

How much fluid is missing and over what time period/mileage?

 

As pads and shoes wear, brake fluid will need to be topped off because the pistons in the calipers, and the brake cylinders retract to ever-increasing distances from their "new pad/shoe" location. Thus more of the system's fluid is contained inside the caliper's/cylinder's piston bore and not in the reservoir where you can see it.

 

GD

[idosubaru]

the question will be over how long of a period is the fluid level decreasing?

this is either normal or extremely urgent (and dangerous).

 

it's actually normal for the level to drop. as the brake pads wear the nominal position of the caliper piston increases. this increases the volume of fluid in the caliper behind the piston and thus decreases the master cylinder volume. that's a very minor amount and it "goes back up", so to speak, when you install new brake pads and push the pistons back into the caliper bores to make room for the new, and larger, brake pads.

 

now...if it's loosing fluid quickly then you're leaking fluid. this needs to be addressed immediately. you will loose braking and depending what's going on it could be catastrophic in results.

 

it's fairly easy to find leaks. look under the brake fluid reservoir, look at the brake calipers and follow the fluid lines. wet spots on the lines should be obvious.

 

there's a chance a caliper is leaking at the piston seal, this would require removing the brake pads to inspect.

 

***edit*** i was typing when GD was as well.

[Turbone]

***edit*** i was typing when GD was as well.

 

If you got to the point, that wouldnt happen :-p:lol:

 

Check the Hill Holder if it has one. I've had 2 of my EA81's leak enough to lose fluid after a time.

[TheSubaruJunkie]

Brake fluid is going to destroy your paint as well. You'll know if there is a long lasting leak, if you notice paint bubbling and flaking off of a certain area. That would be where the fluid is running from. It will eat through the primer and leave you with bare metal. So it shouldn't be too hard to spot.

 

If there are no signs of paint damage, then chances are the leak is somewhere else. Maybe comming from a caliper, or somewhere along the line.

 

Look under the car, cause it will also eat through the rust proofing they spray under your car. May help you identify where the leak is.

[nipper]

If you are still loosing it after checking the above, its possible you are burning it. Your Master Cylinder is old enou to be leaking. You have a giant vacume canister on one side of the master cylinder connected to the engine. If its leaking, the brake fluid can get sucked into the engine. Check the inside of the booster hose, does it smell like brake fluid?

 

 

nipper

[Virrdog]

As pads and shoes wear, brake fluid will need to be topped off because the pistons in the calipers, and the brake cylinders retract to ever-increasing distances from their "new pad/shoe" location.

 

GD

Some people say don't top it off, because if it's low enough then you probably need new pads or shoes. Personally, I am a topper.

 

Along with the other possibilities, if you have rear drums and the shoes are all the way gone... the seals can pop out of the wheel cylinder and leak brake fluid into the drum. You will see the backing plate look kind of wet. Ask me how I know this...

[Caboobaroo]

I've also seen a bad mastercylinder cause brake fluid to mysteriously dissappear. If the MC leaks into the brake booster, the vacuum of the engine will suck it up into the intake and be gone. Only way to know is to pull the vacuum line off of the brake booster and look to see if its wet inside of it. I've seen it a couple times before. My RX is leaking a bit there too but the paint on the brake booster is starting to peel which lead me to the leak I have:-\

[McDave]

I've also seen a bad mastercylinder cause brake fluid to mysteriously dissappear. If the MC leaks into the brake booster, the vacuum of the engine will suck it up into the intake and be gone. Only way to know is to pull the vacuum line off of the brake booster and look to see if its wet inside of it. I've seen it a couple times before. My RX is leaking a bit there too but the paint on the brake booster is starting to peel which lead me to the leak I have:-\

I always just unbolt the mc from the booster and have a look at the back of the mc. You can leave the lines connected so if the mc isn't leaking you can just bolt it back up without having to bleed the brakes.