Altitude Braking

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

 

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.

 

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.

 

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.

 

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

 

This sounds like the "barking brake" syndrome.
See http://priuschat.com/forums/prius-technical-discussion/19051-my-brakes-barking-me.html for past discussions.
- Ed

 

Yep, it happens at high altitude. When it first happened to my 2004 at Lake Tahoe several years ago, the dealer there said it might be the brake stroke simulator valve ( if I remember correctly). The dealers at low altitude had never heard of such a problem.
Last time I went over the Sierras it didn't happen,whether for too low altitude or an aging system, I don't know.

 

I hope it wasn't the same guy at that dealership who told me my tires were 'dangerously overinflated', and let some air out after a contentious discussion. The maximum pressure with which he would allow the car leave the shop left them underinflated once they were cold and the car descended to sea level.

 

I live at a much higher altitude and have no such brake problems. I doubt it is altitude related, only a coincidence.

 

This is a well-known problem and is documented here:
http://priuschat.com/forums/toyota-.../29211-tsb-br001-07-brake-actuator-noise.html

The problem usually manifests itself at a higher altitude. For example my 2004, when at Lake Tahoe (6,200 ft elevation) will produce that squeaking sound. No issue at lower elevations.

Although the problem may be irritating, the braking system is not impaired.

 

I do trust what the Tahoe dealer said about the stroke simulator valve, though it was only an over the phone diagnosis, on the basis of several cars they had checked out for the same symptom. Mainly because the same thing recurred 2 more times on separate trips to Tahoe and has never occurred down in the flats, or even as low as 5,000 feet. It was unnerving the first trip, knowing there was a long downhill trip to come.
It was not the "barking" I see described on other messages here. Every time I pressed the brake pedal, no matter how fully, there would be this sort of sighing squeak. Brake function never seemed to be affected, and I've got my original linings at 180k mi.

 

Perhaps it is a function of delta altitude instead of altitude. It seems like those that have it happen are going up to these altitudes from something lower whereas mine sits at those "high altitudes" at a minimum most of the time.

 

Maybe that's it. I bet SuperDprius and Qbee42 would agree with me that the noise we're talking about doesn't act like the barking actuator noise many of these comments are about.

 

Wow interesting.