The other day my brakes went out when it was hot out and I couldn't stop at low speeds, as my brake pedal would sink to the floor. Even pumping the brakes did little to stop the car. However, above 5mph or so, my car would slow itself just fine until that last stopping bit at low speed/RPM. I managed to get the car back to my garage, where it's been sitting since.



I ran those tests, and it passes all of them. However, my brake fluid is low, and my pedal feel is very soft when the car is at idle. I see absolutely no leaking brake fluid anywhere, including under the master cylinder.

Does this sound like my master cylinder is bad? I haven't bled my brakes since I upgraded them months ago, and they worked perfectly until recently.

 

you must be leaking from somewhere if the fluid is low. Did you look inside the car where the brake pedal goes into the booster? Clean all surfaces underneath the car around brake lines. Check the prop valve as well for leaks.

 

Do you have disc or drum brakes in the rear? they are disc you will notice leaks right away. If they're drum that pull off the drum. Yoy might have bad wheel cylinders. Check those by pulling back the rubber boot on them. If it's wet behind them then thy're bad so replace them.

 

another place many forget to check for a fluid leak is from the rearmost seal on the master, when it leaks, beacuase its exposed to vacuum, it gets sucked into the booster. eventually it can puddle up in there so bad, the motor will injest brake fluid. take the master off of the booster a little, and peek inthere with a flashlight. if you see anything its a master