funny noise when braking at slow speeds

<div class='quotetop'>QUOTE(fernsmom @ Sep 4 2007, 06:30 PM) [snapback]506792[/snapback]</div>

Question 1: The buzzing/whining is normal. If you can hear it, your ears are very good 'cause it's very subtle. Remember when you brake, the electric motors work like generators and put electricity back into the battery. There is a silver box under your bonnet with a Hybrid Synergy Drive logo on it. That's called an inverter. It's job is to convert one voltage into another by using high frequency on/off switching of transistors. What you're hearing is the high frequency waveform that controls the switching of those transistors. When you brake, the inverter has to carefully regulate the current being dumped back into the battery by controlling how fast it switches. That's why you can sometimes hear the frequency of the whining/buzzing change.

check out my site: http://www.myprius.co.za/Prius_inverter.htm



Questions 2: never had that problem...

 

There is also a brake accumulator pump which makes a little buzzing sound when it runs. It builds pressure for the power brakes, since the Prius cannot use engine power like normal cars. The brake accumulator pump runs about every third time you press on the brake pedal (on the average).

Tom

 

Thanks to the original poster and everyone who replied. I just got a prius last friday and I was wondering about that sound as well.

 

<div class='quotetop'>QUOTE(leachboy @ Sep 9 2007, 07:47 PM) [snapback]509756[/snapback]</div>

It's the most common question I answer.

Tom

 

On item 2, the rattling left air vent, I had a similar problem. I kept taking the silver plastic assembly on and off trying to figure out the problem, and I think I finally made it go away.

Pulling that plastic assembly off is kind of tricky because it's a fairly large assembly with several retention clips that attach to the dash assembly. I've cracked a few plastic pieces here and there taking it on and off too many times, so be careful...never fun to mar a new car, right?

Regardless, in my case, there were several yellow plastic clips that attach to the silver assembly. These clips kind of 'float' on the silver assembly when in place, which allows them to align and contract/expand to provide retention when inserted into the dash assembly. I found that by taking the yellow clips off and putting a few layers of tape (i.e. Scotch tape) to make the tip of the fin that the yellow clips attached to a little thicker, it cut down on the amount of 'float' for those clips. After re-inserting, my rattles went away.

At least in my case, there was "too much" play between the yellow plastic clips and the fins they attach to on the vent assembly. Putting the tape in took away alot of the play and also the associated rattle.

Hope that works out to be your issue and this helps...

Mike

 

On item 2, the rattling left air vent, I had a similar problem. I kept taking the silver plastic assembly on and off trying to figure out the problem, and I think I finally made it go away.

Pulling that plastic assembly off is kind of tricky because it's a fairly large assembly with several retention clips that attach to the dash assembly. I've cracked a few plastic pieces here and there taking it on and off too many times, so be careful...never fun to mar a new car, right?

Regardless, in my case, there were several yellow plastic clips that attach to the silver assembly. These clips kind of 'float' on the silver assembly when in place, which allows them to align and contract/expand to provide retention when inserted into the dash assembly. I found that by taking the yellow clips off and putting a few layers of tape (i.e. Scotch tape) to make the tip of the fin that the yellow clips attached to a little thicker, it cut down on the amount of 'float' for those clips. After re-inserting, my rattles went away.

At least in my case, there was "too much" play between the yellow plastic clips and the fins they attach to on the vent assembly. Putting the tape in took away alot of the play and also the associated rattle.

Hope that works out to be your issue and this helps...

Mike

 

I was wondering about the rattle reported by many of our US friends....could this be an issue with the Left Hand Drive dashboard?

Anybody from RHD countries have similar rattles?