Altitude Braking

[Vince Kame]

I recently went to Flagstaff, AZ elevation approx 7000 feet. When there my brakes made a squeeking noise when I depressed the pedal. Not from the pads but from the system. Also after I turned the car off the pressure release/equalizing noise was different than the norm as well. After i returned to Phoenix and lower altitude the noise stopped. Has anyone else had this happen at higher than the normal altitude or know of a reason this may occur.

[qbee42]

It shouldn't be related to altitude. The brake system is sealed, so the ambient pressure is not an issue unless you are on the moon or the bottom of the ocean. I suspect it was coincidence.

Tom

[David Beale]

The squeaking noise when you apply the brakes is from the regeneration. Perhaps it's too noisy in Phoenix for you to hear?

The noise you heard when you shut the car off was the fuel tank pressure release (through the carbon canister of course). It goes on for quite a long time (heard Pearl make this noise yesterday and waited for it to stop, and it was a long wait ).

A change in ambient temp and pressure can make a lot of difference on how the cars systems work and what noises they make/how loud they are.

[Betelgeuse]

Originally Posted by qbee42

It shouldn't be related to altitude. The brake system is sealed, so the ambient pressure is not an issue unless you are on the moon or the bottom of the ocean. I suspect it was coincidence.

Tom

Moreover, if the sound is coming from the regenerative system, there should be no hydraulic/pressure concerns at all.

I second (third?) the thought that there's no reason to have altitude-based differences. Perhaps David is right that it's too loud in Phoenix to hear it.

[SuperDPrius]

Interesting ...

I was in Flagstaff this past weekend also, and experienced something similar. I drove up on Friday evening, and Saturday morning noticed a strange squeak/chirp when I first depressed the brake pedal that sounded like it came from under the center console. I could reproduce this repeatedly - even if I was only tapping the brake. This is not the high-pitched whine that I normally hear when regenerative braking. That afternoon, the squeak was gone. The next morning, it did not come back.

Never happened before, never again. It almost sounded like a squeaky piston or something, but wouldn't have been the actual brake piston because I was braking very lightly at speeds above 8mph.

[qbee42]

The brake pedal actuates the master cylinder piston no matter what the speed of the car. If the power brakes are working okay, the master cylinder pushes against the stroke simulator, which is just a spring loaded piston. Either of these pistons or any part of the brake pedal linkage could be making this squeaking sound.

Tom

[ecprius]

This sounds like the "barking brake" syndrome.
See My Brakes are Barking at Me for past discussions.
- Ed