Losing brake fluid mysteriously

[Ifirefight]

2001 with the dreaded ABS system. Was having issues with the dash brake warning light,buzzer,trac, abs lights coming on and going off after a while. Decided to bleed the brakes a few weeks ago. Seemed to help as far as the warning lights not coming on all the time. Checked fluid level yesterday, it was at the low mark. Added fluid. All is good. My question is where did all that fluid go? I park in the same spot, no drops on the ground and no fluid anywhere under the vehicle. Is it possible that there was air trapped in the lines and it has since worked its way out?


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[19963.4lsr5]

As pads ware the fluid level goes down. When fluid gets to the minimum line you are supposed to check your brake pads and shoes.

Sometimes the rear wheel cylinders leak and it’s not obvious until you remove the rear drums.


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[Kanoe]

I don't think air in the system would be it, it's a sealed system so air shouldn't be in there and couldn't work its way out.

There is not a lot of volume there. Maybe you wouldn't see a drip. It would only be a couple ounces over several weeks? Could you have a bleeder not quite tight enough? It would likely leak under pressure more so than resting. Get a helper to tromp on the brakes and look under for weeping.

I don't know if it's possible for the master cylinder to leak into the booster but maybe. That's one spot you wouldn't see.

 

[BrianK14]

Agreed with all that 19963 said above

 

[brillo_76]

+ 2 with the other 2 users. If your brake system doesn't have any leaks. It goes to min line. Brake are warn out. If a small seep in the back shoes can be hidden for a while.

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[Honda pc]

I thought 4runner were plagued often by leaky wheel cylinder in back.. If its drum brakes.

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[Kanoe]

I thought 4runner were plagued often by leaky wheel cylinder in back.. If its drum brakes.

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You don't hear much about it on this forum. Maybe 1 or 2 over the years but not a common complaint like the rear ale seals.

 

[rightyouareken]

Did you follow the instructions on the master cylinder reservoir for how to properly check the fluid level? On the 2001-2002s with the hydraulic brake booster you need to pump the brake pedal ~40 times with the truck off to purge the pressure from the accumulator before checking the level. Once you turn the truck on and the system "pumps up" the fluid level drops down a bit, so if you top it off with it pressurized, the fluid may be overfilled.

 

[Ifirefight]

Did you follow the instructions on the master cylinder reservoir for how to properly check the fluid level? On the 2001-2002s with the hydraulic brake booster you need to pump the brake pedal ~40 times with the truck off to purge the pressure from the accumulator before checking the level. Once you turn the truck on and the system "pumps up" the fluid level drops down a bit, so if you top it off with it pressurized, the fluid may be overfilled.

Yes, I did follow the instructions. I have the service manual for the 01 4Runner. I will pull the tires off and check the pads and drums in the rear. Thanks for the support.


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[rightyouareken]

Yes, I did follow the instructions. I have the service manual for the 01 4Runner. I will pull the tires off and check the pads and drums in the rear. Thanks for the support.


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Ok cool. It's an easy thing to miss and is unusual for most cars. Good luck finding the culprit.

 

[Ifirefight]

UPDATE. Been meaning to update this. It was a bad rear brake cylinder. Easy fix and cheap. I replaced both of the rear ones to be safe. [emoji106]


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[gamefreakgc]

UPDATE. Been meaning to update this. It was a bad rear brake cylinder. Easy fix and cheap. I replaced both of the rear ones to be safe. [emoji106]


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Great job being attentive to the signals your car was giving you! A lot of people would have just kept filling it up until the leak got worse and worse.

 

[Sarki]

Did you follow the instructions on the master cylinder reservoir for how to properly check the fluid level? On the 2001-2002s with the hydraulic brake booster you need to pump the brake pedal ~40 times with the truck off to purge the pressure from the accumulator before checking the level. Once you turn the truck on and the system "pumps up" the fluid level drops down a bit, so if you top it off with it pressurized, the fluid may be overfilled.

This point is very true. I realized this after replacing my rear shoes & drums and rebuilding bell cranks. I bled the entire system with Motive power bleeder with great results.
I filled reservoir up to max level and over next few days noticed the level is lower in the master reservoir after driving. Almost topped it up to max level again but waited overnight to check next day.
Fluid level was back at max level next day.
Monitored this over following weeks and noticed exactly what you have said in your explanation.
I now have very good working brakes and an effective and properly working parking brake.

 

[OliviaBall]

You need to check carefully all the hoses and clamps, usually it is the main problem if fluid disappearing. I had the same problem and not only with the brake fluid, but with engine antifreeze as well. When I was stopping the engine, I was hearing how the fluids were getting out little by little and I was feeling the smell of those. That scared me a lot and I thought that the car is dead and there is no chance to repair it. So I decided to read more about this and I realized that I can repair everything by myself. Now everything is works well and I am very thankful. I would recommend you not to hesitate to learn more information about braking system and to understand how everything works and what fluid your car needs.