Disappearing brake fluid, but not leaking anywhere. - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 8 Old 05-15-2019, 10:54 AM Thread Starter
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Disappearing brake fluid, but not leaking anywhere.

I keep having to add brake fluid to the master cylinder reservoir periodically when the "brake" light in the dash is illuminated. I've checked the wheel cylinders and calipers and they are not leaking. The master cylinder and reservoir are dry on the outside, so no leaks there. It's been doing this for quite a while. Where is the brake fluid going?


The brakes operate normally, EXCEPT on long trips over an hour during which the pedal goes to the floor occasionally. A 2nd pump of the pedal and all is normal for a while. When driving local errands I have no issue with the brakes......only on long trips.

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2004 Corolla LE 374K+ miles.
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post #2 of 8 Old 05-15-2019, 02:23 PM
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How long is it between top-ups? It's normal to need more fluid as the calipers and wheel cylinders push outward compensating for wear. If it's just once in six months, or if you're heavy on the brakes, it might be normal/


If you're needing to top up weekly or monthly with normal driving, that's a bit much. Could the fluid be leaking out the piston end of the master cylinder? You would have to remove it to find a leak there.
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post #3 of 8 Old 05-15-2019, 10:18 PM Thread Starter
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Originally Posted by Wekadog View Post
How long is it between top-ups? It's normal to need more fluid as the calipers and wheel cylinders push outward compensating for wear. If it's just once in six months, or if you're heavy on the brakes, it might be normal/


If you're needing to top up weekly or monthly with normal driving, that's a bit much. Could the fluid be leaking out the piston end of the master cylinder? You would have to remove it to find a leak there.
I'm not heavy on the brakes and I hardly drive this truck at all. Maybe 2K miles per year. It's definitely much, much more than normal compensation for wear. When you say "leaking out the piston end of the master cylinder", do you mean where it connects to the vacuum booster? I've only once replaced a master cylinder, and that was on a 1997 Camry. If it's leaking from the piston end, does that mean it's leaking into the booster? If so, does that mean the booster is bad, or does that mean the master cylinder is bad?

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post #4 of 8 Old 05-15-2019, 10:38 PM
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. . . "leaking out the piston end of the master cylinder", do you mean where it connects to the vacuum booster? . . . does that mean it's leaking into the booster? If so, does that mean the booster is bad, or does that mean the master cylinder is bad?
If fluid is leaking from the master cylinder, the MC is bad. The fluid could be pooling up inside the booster.

You might like to remove the MC to look for signs of fluid leakage. At that point, it makes sense to disassemble and inspect the MC. If it's just corrosion, a good cleaning might fix your issue. If the seals are worn or dried, you'll need to change them, or just fit a new MC.
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post #5 of 8 Old 05-16-2019, 12:34 AM
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^ yess.. check the massa cylinder... leaks internally









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post #6 of 8 Old 05-16-2019, 08:48 AM Thread Starter
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Originally Posted by Wekadog View Post
If fluid is leaking from the master cylinder, the MC is bad. The fluid could be pooling up inside the booster.

You might like to remove the MC to look for signs of fluid leakage. At that point, it makes sense to disassemble and inspect the MC. If it's just corrosion, a good cleaning might fix your issue. If the seals are worn or dried, you'll need to change them, or just fit a new MC.
Quote:
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^ yess.. check the massa cylinder... leaks internally

Will remove it and see. I've got too much on my plate currently, but will report back here whenever I get to this. Thanks Wekadog and Blackness.

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post #7 of 8 Old 05-16-2019, 10:09 PM Thread Starter
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I decided to take another look at the wheels before removing the master cylinder. It's possible I was mistaken and now I think my rear driver's wheel cylinder is leaking. I noticed the paint on the backing plate was all peeling and damp, which is something brake fluid can do (removes paint). I decided to take the drum off to take a look-see. Can't get the drum off, though. Will try again tomorrow. Will let ya'll know.

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post #8 of 8 Old 05-16-2019, 11:26 PM
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Quote:
Originally Posted by John Anthony View Post
I decided to take another look at the wheels before removing the master cylinder. It's possible I was mistaken and now I think my rear driver's wheel cylinder is leaking. I noticed the paint on the backing plate was all peeling and damp, which is something brake fluid can do (removes paint). I decided to take the drum off to take a look-see. Can't get the drum off, though. Will try again tomorrow. Will let ya'll know.
- retract the shoes a bit to get the drum off
- then manhandle it a bit
- glad you found the problem!
















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