Have an SC400.

When I press the brake pedal I get a constant squeaking sound. When pressing the brake to engage drive from park it will squeak after the first 10% of pedal travel.
When breaking at speed down to a stop it brakes between 60-100% brake pedal travel.

The noise is most definitely coming from inside the car RIGHT at the pedal. This happens about 50% of the time I drive the car, usually from a cold start but not always. It will go away as I drive after a few stops.

The noise is like a medium pitch sqeak/squeal. Almost like when letting air out of a balloon, just not as high pitched. I could hold it at 10% pedal travel or 50% and the volume and pitch don't change at all. It only goes away when I let go of the brakes when it's happening.

With all that info out there, what could cause this? I've read a bunch of kinda similar posts and most seem oriented to pads, but those are fine, and the sound is coming directly from the pedal itself. Some have suggested spraying wd-40 on the pedal linkage, but I'm not sure that's the best idea.

edit:
Clarification after driving it again. It does change loudness and pitch depending on pressure on the pedal/pedal travel. It's 2-3 different stages it seems, but it's not gradual, it jumps in pitch. Soft press is lower, mid press gets higher pitched and louder, hard pressing seems to increase in volume a bit more.

 

I'm FAR FROM a decent mechanic, but are you loosing any fluid? or showing signs of air getting in system? the balloon reference reminds me of a sound one could get from a hose with a hole/tear. I had a similar balloon squeal with a hole in a vacuum line. Hydraulics may sound similar.

Are you SURE its inside the car? any possibility its under the hood?

Just a few potentially useless thoughts until a real mechanic answers ;-)

 

Thanks for the feedback.

It is possible it could be coming from the engine compartment, as it sounds to be coming from the footwell and that's the closest part to the engine bay.

I'll get someone to press the breaks and check around the hood next time it happens, and monitor fluid levels.

It's a newer car for me, so I haven't had time to track how these things are going. It apparently sat for a bit (garaged), the guy used to DD not too long ago though. Was thinking it might have been a result of sitting for a while.

 

Do you hear the sound only when it is cold?

My theory is that it is the sound of air getting in the the atmosphere side of the booster (the other side is the vacuum).

I guess soon I will need to be in astronaut position to check if the inlet is getting clogged.

Salim