Spring sound when braking

[smithBYU85]

I have a 2004 Prius and recently made a long trek from Illinois to Utah for school. When in Wyoming and then in Utah, when I braked I heard a sound that sounded like a spring being hit, a "boing" sound. It occured most when I was coming to a complete stop, and it didn't seem to matter if the car was warm or not. The sound stopped yesterday after I had called the dealer to make an appointment. The tech checked the car over and didn't find anything (no surprise). The car's brakes normally and regen seems to be happening without any problems. It is this car's first trip in the mountains, and conversely, high altitude. Has anybody had a similar experience?

[bgdrewsif]

This has been discussed many times... I wondered about this for a long time too... It is normal... something to do with the hybrid system... but no need to worry!

[qbee42]

<div class='quotetop'>QUOTE(bgdrewsif @ Aug 28 2007, 10:46 PM) [snapback]503565[/snapback]</div>

This has been discussed many times... I wondered about this for a long time too... It is normal... something to do with the hybrid system... but no need to worry!
[/b]

The normal braking sound is a buzz or rattling sound from behind the drivers foot well. That is the brake accumulator pump which runs about every third time you press the brake. It supplies power for the brakes, since engine vacuum is not always available on the Prius.

A boing or spring sound might be different, depending on what the OP thinks a spring sounds like. The brake peddle on a Prius uses hydraulics to press against a loaded spring. The spring gives the brake peddle travel and resistance so that the braking action feels normal (as it would in a normal car). It may be possible that the loading spring was making some noise. It doesn't seem likely, but noises can be weird. I haven't looked to see if there is a peddle return spring. That could also be a culprit.

Regardless, I wouldn't worry about it unless it starts doing it again.

Tom